Metal-Free Oxidative CâC Coupling of Arylamines ... - ACS Publications

Article pubs.acs.org/joc

Metal-Free Oxidative C−C Coupling of Arylamines Using a Quinone-Based Organic Oxidant Sudhakar Maddala, Sudesh Mallick, and Parthasarathy Venkatakrishnan* Department of Chemistry, Indian Institute of Technology Madras, Chennai 600 036, Tamil Nadu, India S Supporting Information *

ABSTRACT: A variety of arylamines are shown to undergo oxidative C−C bond formation using quinone-based chloranil/H+ reagent as the recyclable organic (metalfree) oxidant system to afford benzidines/naphthidines. Arylamines (3°/2°) designed with various substituents were employed to understand the steric as well as electronic preferences of oxidative dimerization, and a mechanism involving amine radical cation has been proposed. The tetraphenylbenzidine derivative obtained via oxidative C−C coupling has been further converted to blue-emissive hole-transporting material via a simple chemical transformation. This study highlights the preparation of novel HTMs in a simple, economic, and efficient manner.

■

INTRODUCTION Tetraarylaminobiaryls (TAABs) are an important class of organic compounds that serve as excellent hole-transporting materials (due to low oxidation potential) in organic light-emitting diodes (OLEDs),1a organic solar cells (OSCs),1b pervoskite solar cells (PSCs),1c sensors,1d,e etc. Literature reports to date for the preparation of TAABs (benzidine/naphthidine derivatives) via C−C/C−N bond formation have been overwhelmed by utilization of transition-metal-based cross-coupling reactions such as, Suzuki coupling,2a Stille coupling,2b Kumada coupling,2c Ullmann coupling,2d,e Buchwald−Hartwig amination,2f and nucleophilic aromatic substitution reaction (SNAr),2g etc.2 These reactions often involve expensive catalysts/ligands, strong bases, high temperatures (80−120 °C), long reaction duration (8−24 h), side reactions such as dehalogenation and homocoupling, and contamination of metal impurities in trace amounts with the isolated products. Another approach that is relatively straightforward for the construction of C−C bonds between arylamines has been oxidative coupling, which is once again dominated by the use of various metal salts (Scheme 1a).3 On the flip side, this oxidativetype of reaction with di-/triarylamines is generally uncontrollable leading to several side products resulting in low yields. Hence, for an efficient preparation of TAABs, development of metal-free, ecofriendly, economic, simple synthetic protocols is essential and a highly desired strategy. In relation to this, Ichikawa et al. developed a synthetic method using an organic oxidant, 1,8-bis(diphenylmethylium)naphthalenediyl dication (NBDM), for the self-coupling of N,N-dialkylanilines (Scheme 1b); however, the self-coupling of tri-/diarylamines was not reported.4 In addition, the oxidant NBDM used was commercially inaccessible, and most of the reactions were carried out at −78 °C. Keeping these drawbacks in mind, we envisaged a room-temperature © 2017 American Chemical Society

synthesis of TAABs using a commercially available quinone as an organic oxidant, since quinone reagents are popular oxidizing agents in organic synthesis, especially, in oxidative coupling/ cyclodehydrogenation (Scholl) reactions.5 Under this category, we figured chloranil is a commercially available, cheap, recyclable organic oxidant, whose potential in oxidative coupling reactions still remains under-explored.5 In addition, an electron transfer reaction between chloranil (CA, Ered = 0.02 V vs SCE)6 and triphenylamine (TPA, Eox = 0.98 V vs SCE)7 couple is feasible for the oxidative C−C bond formation to TAABs. To this basis, and in continuation to our research efforts on the design and synthesis of novel hole-transporting materials,8 we attempted to achieve tetraarylbenzidines (TABs) or tetraarylnaphthidines (TANs) and diarylbenzidines (DABs) or diarylnaphthidines (DANs) from the corresponding triarylamines (TAAs) and diarylamines (DAAs), respectively, via a metal-free oxidative C−C coupling strategy utilizing chloranil/H+ (quinone-based reagent) as recyclable organic oxidant (Scheme 1c), and the results are consolidated here. To the best of our knowledge, this is the first report that uses chloranil as the recyclable organic oxidant for the oxidative C−C bond formation of TABs. As opposite to the earlier reports,3e−g we have shown the role of sterics and electronics, the positional influence of substituents, and the compatibility of various functional groups under the oxidative coupling reaction conditions of various arylamines. In addition, the mechanism of formation of the dimeric product via an amine radical cation has been proposed with the help of UV−vis-NIR absorption spectroscopy and based on other literature reports/evidence. The synthesized benzidine derivative Received: June 3, 2017 Published: August 17, 2017 8958

DOI: 10.1021/acs.joc.7b01377 J. Org. Chem. 2017, 82, 8958−8972

Article

The Journal of Organic Chemistry Scheme 1. Oxidative Coupling Protocols of Various Arylamines Explored in the Literature and in This Report

has been further structurally elaborated to offer highly fluorescent analogues that display strong blue emission.

for this reaction. Replacement of MSA by various other Brønsted acids was not fruitful (entries 4−6, Table 1). Changing the solvent either to CH3CN or to toluene led to inferior results (entries 7 and 8, Table 1). Decreasing the loading of oxidant affected the yields and prolonged the reaction duration (entries 9 and 10, Table 1). It is readily discernible from Table 1 that the oxidative coupling reaction of TPA using an organic oxidant CA in the presence of MSA is found to complete in less than a minute providing near quantitative yields of the dimeric product (TPB) at room temperature. This methodology is cheap, efficient, and ecofriendly from the point of view of the ability to recycle/reuse tetrachlorohydroquinone formed after the reaction by aerobic oxidation to chloranil (also see the SI for recyclability experiments).11 With the best conditions in hand, we performed a gram-scale reaction of simple triphenylamine 1 which again provided the oxidative dimer N,N,N′,N′-tetraphenylbenzidine 2a (TPB) quantitatively in just 1 min at room temperature (Table 1 and Figure 1). Though the para-positions of TPB are open so that the TPB is very much prone to oxidation when compared to TPA (vide infra), we did not observe the formation of any other oligomeric side products during the course of the reaction. Encouraged by this result, we screened several triarylamine derivatives (3° amines, such as 1, whose Eox ranging between 0.82 and 1.25 V vs SCE, see the SI for details) possessing different para substituent(s) on the aryl rings (Figure 2); a variety of mono- (two open para positions) and disubstituted (one open para position) triphenylamine (TPA) derivatives were attempted. Triphenylamines carrying substituents such as methyl, bromo, fluoro, cyano, nitro, ester, and phenyl at the 4- and (or) 4′-positions underwent successful oxidative coupling to provide very good yields (≥89%) of tetraphenylbenzidine (TPB) derivatives (2b, 2c, 2f−j, 2n−p, Figure 1). TPA containing functional groups such as tert-butyl, methoxy, aldehyde, ketone, carboxylic acid, dicyanovinylidene, and dibromovinylidene at para positions offered the dimeric products (2d, 2e, 2k, 2m, 2q−u, Figure 1) in good to moderate yields (30−89%); when two aldehyde groups were present at the para positions, the reaction did not proceed at all (as in 2l) as observed previously,3f and the starting material was recovered completely. The results observed here (for 2b, 2c, 2f, 2g, 2i, and 2j) are far superior than those obtained

■

RESULTS AND DISCUSSION The oxidative C−C coupling reaction conditions were optimized by choosing triphenylamine 1 as the model substrate, and results are summarized in Table 1 (for more details, see the SI). As may Table 1. Optimization for the Oxidative C−C Coupling of Triphenylamine 1a

entry

deviation from standard conditions

yield (%)

1 2 3 4b 5b 6b 7b 8b 9 10

none without chloranil without MSA p-TSA instead of MSA TfOH instead of MSA TFA instead of MSA CH3CN instead of DCM toluene instead of DCM chloranil (1.0 equiv) chloranil (1.5 equiv)

>99 0 0 11 25 51 36 22 82 97

a

All of the reactions were run at rt until the starting material was consumed completely (as identified by TLC). bTLC showed the presence of 1 along with some polar spots.

be seen, the best conditions achieved for the oxidative C−C coupling are TPA (0.8 mmol), CA (1.6 mmol), and methanesulfonic acid (MSA):dichloromethane (DCM) (1:10, v/v), which provided tetraphenylbenzidine (TPB) 2a in quantitative yields at room temperature in 1 min (entry 1, Table 1), and any deviation from the above conditions resulted in discouraging results (entries 2−10, Table 1). Treatment of acid in the absence of chloranil failed to proceed (entry 2). Similarly, oxidative coupling of TPA with CA in the absence of MSA did not lead to the dimeric product (entry 3, Table 1).6,9,10 The above control experiments confirmed the necessity of both MSA and chloranil 8959


Article

The Journal of Organic Chemistry

Figure 1. Oxidative dimerization of various triarylamines containing substituents in different positions in the presence of chloranil/H+. X-ray determined molecular structures of 2h (F atoms are disordered at two sites; see the SI for details) and 2zd.

in earlier reports.3f,g The oxidative dimer 2h was crystallized and the structure was confirmed by single-crystal X-ray diffraction analysis (Figure 1). The above set of reactions suggest that oxidative coupling of electron-rich TPAs proceeds very efficiently (1 min, >99%), and the electron-poor TPAs are relatively less efficient (1 min, 90−96%); the same is notably sluggish (30 min to 7 h, 30−72%) when substituents such as methoxy, aldehyde, ketone, carboxylic acid, dicyanovinylidene, and dibromovinylidene are present. It is also observed in all cases that dimerization took place only at the para position and not at the

ortho position, possibly because of steric reasons. Most importantly, a regular synthesis of 2f, 2k, 2m, 2n, and 2q−s from TPB could be very cumbersome leading to a mixture of products that might involve tedious separation procedure,12 which the present method is free of. Thus, this synthetic methodology highlights the ready preparation of the above-said TPB derivatives starting from the corresponding TPAs rapidly in good to excellent yields in one step. Hence, it was highly desirable to study the ortho-substituted and meta-substituted TPA derivatives, as the substituted as well 8960


Article


Figure 2. Oxidative dimerization of various 3° amines, such as diarylalkylamines in the presence of chloranil.

than 3b and 3d (ca. 45°) due to the methyl susbtituent(s) ortho to the ring−ring bond and hence difficult to further oxidize when compared to the planar meta/para analogues 2v and 2w/2c. At this juncture, it is important to note that 2-substituted TPAs form dimers (2za−d) only at the unsubstituted phenyl rings rapidly in excellent yields (>99%, Figure 1), irrespective of whether the phenyl ring contains electron-donating or -withdrawing groups. The reason as to why in the case of 2-methyltriphenylamine (Eox = 1.02 V vs SCE)13 the dimerization did not occur at the 2-methyl-containing phenyl ring (para position open and electron rich), in contrast to 3-methyltriphenylamine could be understood from the following explanation. In 2-substituted TPA cases, the lone pair on the nitrogen atom is engaged effectively with the unsubstituted phenyl rings when compared to the ortho-substituted phenyl ring, as the ortho substituent on the phenyl ring imparts sterics, hence twists, and restricts resonance. From above, it is observed that electron-rich TPAs are the ideal candidates for oxidative coupling reaction in which the electronrich ring undergoes dimerization. The 2,2′-dicyano-substituted TPB dimer 2zd was confirmed by single-crystal X-ray diffraction analysis (Figure 1). Clearly, one may notice a twist angle of ca. 50.4° (relative to that of phenyl/biphenyl) exhibited by the ortho-substituted phenyl ring in 2zd. We then turned our attention toward expanding the scope of the reaction with diarylnaphthylamines (as in 4, Figure 1). It is expected that attachment of naphthyls would provide TAA substrates endowed with steric as well as electronic features for further investigation. To our surprise, under the above-optimized conditions, 2-naphthyldiphenylamine yielded a complex mixture of unidentifiable products, whereas 1-naphthyldiphenylamine offered a mixture of naphthidine (5a, 45%) and benzidine (NPB 6a, 55%) dimers with complete conversion (see 1H NMR, SI). To avoid the formation of NPB and to achieve 4,4′-naphthidine dimer, the possible dimerization sites at the phenyl rings (4 and 4′-positions) in N,N-diphenyl-1-naphthylamine were blocked by tert-butyl groups. Thus synthesized, N,N-bis(4-tert-butylphenyl)-1-naphthylamine,

as the unsubstituted benzene rings would now have open para positions for benzidine formation. Moreover, with orthosubstituted TPA derivatives, one can explore the scenario of oxidative coupling resulting from twisting. As a result, 3-substituted as well as 2-substituted triarylamines were subjected to oxidative coupling reaction which offered dimeric products (2v−z, and 3a−d) in good to excellent yields (Figure 1). As expected, in the case of 3-methyl-substituted TPAs, the oxidative coupling resulted in an inseparable mixture of all possible three products as a result of coupling between two unsubstituted phenyl rings, two substituted phenyl rings, and a substituted and an unsubstituted phenyl ring (the former leads to two homodimers 2v/3a and the latter leads to a cross-dimer 3b), in a relative ratio of 0.3:1.0:1.6, respectively (see the 1 H NMR, SI). Similarly, 3,3′-dimethyltriphenylamine resulted in an inseparable mixture of homodimers 2w (13%), 3c (37%) and a cross-dimer 3d (50%) in a relative ratio of 0.35:1.0:1.34, respectively (see 1H NMR, SI). Indeed, the 3-methyl-containing phenyl ring(s) participated in oxidative dimerization to a major extent in spite of steric effect caused by the methyl groups. This supports the active participation of electron-rich aryl rings in oxidative dimerization. Noteworthy is that when 3-bromotriphenylamine was subjected to oxidative dimerization the 3-bromo-containing phenyl ring did not participate in oxidative dimerization leading to 2y (Figure 1). It is surprising to see the contrasting behavior with donor and acceptor substituents at the 3-position. In order to further understand the influence of sterics in the oxidative dimer formation and to achieve the sterically hindered product directly through oxidative dimerization, a specially designed substrate, that is, 3,4′,4″-trimethyltriphenylamine (with one open para position and a meta methyl substituent in a phenyl ring) was examined. We were pleased to see that it resulted in the sole formation of the sterically congested dimer 2x in very good yields (ca. 82%, Figure 1), in contrast to the oxidative coupling reaction of 3-methyltriphenylamine, which resulted in a mixture of products (2v, 3a,b). The dimers 3a, 3c, and 2x are expected to be twisted (ca. 90°) more 8961


Article


para-position of the phenyl to give the corresponding benzidines (12a−c) and of N-phenyl-1-naphthylamine at the 4-position of naphthalene to offer the naphthidine (12d) derivative in excellent yields (86%, Figure 3).3e It is notable that 3-methyldiphenylamine dimerized at the fourth position of the methyl-substituted phenyl ring to give twisted 12c, like 8d. Interestingly, N-phenyl2-naphthylamine resulted in N,N′-bis(2-naphthyl)benzidine (12e, Figure 3) in good yields. Similarly, the above reaction with N-ethyl-1-naphthylamine afforded the oxidative 4,4′-naphthidine dimer (13a) in 21% yield; however, the reaction was not successful with N-ethylaniline (Eox ca. 0.70 V vs SCE).3e,14 Indeed, studies on oxidative coupling reactions of 1-/2-naphthylamines (2°) or anilines (2°) are very much limited in the literature.3d,e,15,16 The above set of experiments on various arylamine substrates hints to the immediate oxidizing ability of the triarylamine skeleton when compared to diarylalkylamine or the diarylamines and the importance of the electron-rich arylamine substrates for the above C−C coupling reaction. In general, the reactivity trend in the case of oxidative coupling of arylamines under the given conditions follows the order triarylamines (3°) > diarylalkylamines (3°) > diarylamines (2°) > arylalkylamines (2°) ≫ dialkylarylamines (3°) ≈ arylamines (1°). Dialkylarylamines and arylamines (1°) are found to be unreactive under these conditions. This also emphasizes the necessity of a minimum of two aryl groups on the amine nitrogen atom for the oxidative coupling to occur. In addition, it is essential that the arylamines must possess Eox in the range 0.75−1.3 V vs SCE for facile oxidative dimerization. To the best of our knowledge, this is the first report on the synthesis of ortho-/meta-/para-substituted TPBs and tetraphenylnaphthidines (TPNs) via oxidative coupling methods using an organic oxidant.3e−g,15 In general, TPBs and TPNs are very useful compounds in organic electronics; they are commonly used as hole-transporting or emitting materials in OLEDs due to their ability to form glassy amorphous films.1a,17,18 In view of the multistep synthetic procedures involving Pd-/Cu-mediated cross-coupling reactions2a,b,f in the synthesis of unsymmetrically substituted TPBs, the procedure described herein is less tedious, convenient, and very advantageous. Most importantly, the present procedure unfolds the opportunity to achieve various substrates in an efficient fashion, and also proves excellent tolerance toward various functional groups under the above experimental conditions. The electrochemical oxidative dimerization of arylamines was studied previously by various groups in detail.19 In this, the mechanism of electrochemical formation of TPB from TPA was shown to proceed via an electrochemically generated TPA radical cation (TPA•+).19 In addition, there has been an understanding that the oxidative dimerization reactions are purely guided by (i) the redox potentials of the participating triarylamines, (ii) the reactivity (rate of the bimolecular reaction) of the participant triarylamines, and (iii) the stability of the intermediates (radical cation species, vide infra) generated during the course of the reaction. Later, Gopidas et al. demonstrated the presence of TPA•+ in the formation of TPB from TPA using Cu(ClO4)2.3f To glean insights into the mechanism and to investigate the intermediacy of the radical cation in our oxidative coupling reactions mediated by the organic oxidant chloranil/H+, we performed trapping experiments with various agents under the above experimental conditions. Unfortunately, we observed only the formation of TPB dimer. Hence, the course of the reaction was monitored by UV−vis-NIR absorption spectroscopy (Figure 4).3f,20 While TPA absorbs below 370 nm (in dichloromethane solution), the

under the above-optimized conditions, now provided 5b in moderate yields (47%, Figure 1). Replacement of a phenyl ring by an alkyl group in triphenylamine generally decreases the oxidation potential.14 For example, N-methyldiphenylamine possesses an Eox value of 0.84 V vs SCE which is lower than the Eox of TPA.14 As a result, tertiary amines such as diarylalkylamines (of type 7) displayed reduced reactivity under the optimized conditions and required longer reaction times (9−24 h, Figure 2) than triarylamines (1 min to 7 h). For example, when the alkyl groups in diphenylalkylamines were varied from R = Et to Hex to Bz, only moderate yields (59−69%) of the dimeric products (8a−c) were obtained in 24 h. Interestingly, the coupling in case of N-ethyl3-methoxydiphenylamine had occurred at the electron-rich (3-methoxyphenyl) ring and also at a sterically hindered (4-position) site to give a twisted biaryldiamine 8d. One may notice, in the case of N-phenyltetrahydroquinoline, where one phenyl ring is rotation-restricted and the other phenyl is not, that oxidative coupling afforded a dimer at the locked phenyl ring (as in 8e). This could be attributed to the increased planarity/resonance effect exhibited by the tetrahydroquinoline (locked phenyl) ring when compared to the free phenyl ring. In a similar vein, we also investigated the oxidative coupling of N-alkyl-N-phenyl-1- or -2-naphthylamines (as in 9, Figure 2). To our delight, N-ethyl-Nphenyl-1-naphthylamine provided the benzidine derivative 10a in very good yields (87%). Similarly, reaction of N-ethyl-Nphenyl-2-naphthylamine with CA resulted in a phenyl dimer 10b in reasonably good yields in a very facile manner (2 h). Unfortunately, the oxidative coupling of dialkylarylamines, such as, N,N-dimethylaniline (Eox = 0.71 V vs SCE)14 or N,N-dimethyl-1naphthylamine (Eox = 0.75 V vs SCE)14 and N,N-dimethyl-2naphthylamine (Eox = 0.67 V vs SCE)14 was not fruitful. This could probably be due to the relatively very low oxidation potentials (Eox < 0.75 V vs SCE) of the dialkylarylamines when compared to other arylamines. Further, to investigate the feasibility of oxidative coupling reactions of 2° arylamines (as in 11, Figure 3), diphenylamines (Eox ∼ 0.84 V vs SCE),14 N-phenyl-1-naphthylamine, and N-phenyl-2naphthylamine, whose Eox values are higher than N,N-dialkylaniline, were subjected to the optimized conditions, and the results are summarized in Figure 3. It was observed that the oxidative dimerization of diphenylamines was facilitated at the open

Figure 3. Oxidative coupling of various aromatic 2° amines, such as diarylamines and arylalkylamines. 8962


Article


Figure 4. (Left) UV−vis−NIR absorption spectrum showing the intermediacy of TPA•+ during the oxidative coupling of TPA (0.02 M). (Right) Proposed mechanism for the oxidative coupling reaction of aromatic amines (for example, TPA).

UV−vis−NIR absorption spectrum upon addition of 2.0 equiv of chloranil in the presence of MSA revealed development of a broad band between 600 and 800 nm (the color of the solution turned blue) with the absorption maximum centered at around 660 nm. We attribute this spectral feature to the formation of TPA•+, based on previous evidence (Figure 4).20 Moreover, one may notice over time that the absorption band due to TPA•+ decreases in intensity accompanied by a minor red-shift (ca. 25 nm, i.e., 685 nm), along with simultaneous growth of absorption in the regions 410−540 nm and 850−1650 nm (Figure 4). The decay at 660 nm and a proportionate growth at ca. 480 and 1300 nm clearly dictates that these new absorptions originate basically from TPA•+. The growing new band at 480 nm may be assigned to the typical π−π* transition of TPB•+, and the new broad band observed in the near-IR region (1200−1400 nm) is attributed to the intervalence charge-transfer excitation resulting from TPB•+ as reported earlier.21 Based on the above results that suggest the presence of TPA•+ and in comparison to the previously published reports,19−21 we have hereby proposed a mechanism for the formation of TPB starting from TPA in the presence of CA/H+ as the organic oxidant (Figure 4). As may be seen, the first step is the formation of the TPA radical cation (TPA•+) by reaction with CA/H+. The importance of H+ (MSA) and CA in this oxidative C−C coupling reaction is evident from Table 1. It is realized that the generation of radical cations (electron-transfer reactions) is efficient in the presence of MSA or trifluoromethanesulfonic acid (TfOH), and in the absence of which, acceptor CA only forms donor− acceptor complexes with various donors.6,9,10 In other words, the above electron-transfer reaction (endothermic) from TPA to TPA•+ is driven probably by the formation of protonated chloranil that is more electron deficient than its precursor chloranil. The TPA•+ radical cation thus formed in the first step dimerizes in the second step to lead to a dication H2TPB2+, which then loses two protons to give TPB in the third step (Figure 4). As such, the generated TPB is a better electron donor (Eox = 0.69 V vs SCE)3f when compared to TPA. Hence, it can donate an electron either to TPA•+ or to CA and generate TPB•+ which in turn can be neutralized by workup with aqueous NaHCO3/NaOH or triethylamine (TEA).3c,f A similar mechanism involving amine radical cation has also been proposed in oxidative coupling reactions mediated by other chemical oxidants.3 The other pathway could possibly be that TPA•+

undergoes an aromatic electrophilic substitution-type reaction with the neutral TPA followed by deprotonation and aromatization. This pathway we feel is the least possible one here, given the fact that these reactions are very fast and occur mostly in less than 1 min. For comparison, electrochemical dimerization of TPA via TPA•+ to TPB is known to proceed with a bimolecular rate constant value of ca. 103 mol−1 s−1.19a We have further demonstrated the use of this metal-free oxidative coupling method in the preparation of functional molecular materials (Figure 5). The TPB derivative 2k prepared

Figure 5. Polymerizable HT material 14 and blue-emitting HT material 15 synthesized from the TPB-dialdehyde 2k.

from the corresponding 4-formyltriphenylamine via the oxidative coupling was advanced to metal-free synthesis involving Wittig reaction with methyltriphenylphosphonium bromide or Wadsworth−Emmons reaction with diethyl benzylphosphonate to afford compounds 14 and 15, respectively. While compound 14 is a polymerizable HTM,22 the other synthesized phenylenevinylene compound 15 exhibits absorption maximum at ca. 379 nm and emission maximum at ca. 455 nm (blue region, see the SI). Moreover, the compound 15 is observed to be highly fluorescent in the solution state, and its fluorescence quantum yield in chloroform is measured to be 0.37 (for details, see the SI). Certainly, in a similar fashion, variety of simple functional group transformations (via either metal-free or metal-based synthesis) on 2/3/5/6/8/10 may lead to a gamut of molecular materials for various applications. In particular, such tetraphenylbenzidine-based fluorescent materials containing stilbene/ triphenylethene/tetraphenylethene units have been identified as potential fluorescent aggregation-induced emitters (AIE) or solid-state emitters.23 Other than these advantageous characteristics, the nonplanar and propeller-like structure of these benzidine/naphthidine derivatives prevent them from packing efficiently and hinder crystallization. As a result, it offers 8963


Article


4-methoxycarbonyltriphenylamine,31 4,4′-bis(methoxycarbonyl)triphenylamine,32 4,4′,3″-trimethyltriphenylamine,33 3-bromotriphenylamine,34 3-methyltriphenylamine,35 2-methyltriphenylamine,35 4-phenyltriphenylamine,35 2-nitrotriphenylamine,36 2-cyanotriphenylamine,37 N-ethylN-phenyl-1-naphthylamine,38 N-ethyldiphenylamine,39 N-hexyldiphenylamine,40 N-benzyldiphenylamine,41 N-ethyl-1-naphthylamine,42 N-phenyltetrahydroquinoline,43 4-carboxytriphenylamine,44 4-dicyanovinylidenyltriphenylamine,45 4-dibromovinylidenyltriphenylamine,46 and 4,4′-bis(dibromovinylidenyl)triphenylamine47 were synthesized according to the available literature procedures. The triarylamines thus obtained were characterized by 1H and 13C NMR spectroscopy, and the data were verified with the cited literature reports. Preparation of Tetraarylbenzidines via an Oxidative Coupling Method. The general procedure for the synthesis of benzidine/ naphthidine dimers (2−13) from the arylamine precursors via an oxidative coupling method is as follows. General Procedure for the Oxidative Dimerization of Arylamines. A solution of arylamine (0.8 mmol, 1.0 equiv) in dry dichloromethane (10 mL) was cooled to 0 °C, and methanesulfonic acid (1.0 mL) was introduced. After being stirred for few minutes at 0 °C, chloranil (401 mg, 1.6 mmol, 2.0 equiv) was added. The color of the reaction mixture turned blue-green to blue for various substrates. The progress of the reaction was monitored carefully over time by TLC. As soon as the complete disappearance of the starting material was noted, the reaction was quenched with the addition of saturated NaHCO3 solution under ice and worked up as follows. The whole of the reaction contents was transferred into a separating funnel, and the organic contents were extracted into chloroform (3 × 10 mL). The combined organic layer was washed with 2 N NaOH solution (for secondary amines, the organic portions were washed with satd NaHCO3 solution, instead). Now the aqueous portion remained red leaving the organic portion colorless. This was then washed with brine and dried over anhyd Na2SO4, filtered, and evaporated to dryness. The crude product thus obtained was purified by silica gel column chromatography using a hexane−ethyl acetate mixture as the eluent. The pure products were isolated as a colorless solid/liquid to a pale yellow solid/liquid. A typical procedure for the synthesis of tetraphenylbenzidine (TPB, 2a) starting from triphenylamine (TPA, 1) is given below. Typical Procedure for the Synthesis of TPB Dimer 2a from TPA 1.3f,48 To a solution of triphenylamine 1 (200 mg, 0.81 mmol) in dry dichloromethane (10.0 mL) at 0 °C was introduced methanesulfonic acid (1.0 mL). After the contents were stirred for 2−3 min, chloranil (400 mg, 1.63 mmol) was added at the same temperature. The reaction contents immediately turned deep blue. The reaction mixture was allowed to stir further and slowly attained room temperature. The progress of the reaction was monitored carefully by thin-layer chromatography. Upon completion of the reaction (1 min, as identified by TLC), the reaction was quenched by saturated NaHCO3 solution in an ice bath. The organic contents were extracted into chloroform (3 × 10 mL). The combined organic layer was washed with 2 N NaOH solution to remove tetrachlorohydroquinone completely, washed with brine, dried over anhyd Na2SO4, filtered, and evaporated to dryness. The crude product thus obtained was purified by silica gel column chromatography using hexane−ethyl acetate mixtures (5% EtOAc in hexane) as the eluent to obtain pale yellow TPB product 2a in quantitative yield (199 mg, 0.81 mmol, >99%). Tetraphenylbenzidine, 2a.3f,48

them an ability to retain an excellent amorphous and glassy film morphology during conditions of OLED device operation.23

■

CONCLUSION In summary, for the very first time, we have demonstrated that the C−C coupling of various arylamines can be simply effected oxidatively under chloranil/H+ conditions (metal-free, inexpensive, recyclable) at room temperature in an efficient manner. It is observed that the electron-rich arylamines (0.75 V < Eox < 1.3 V vs SCE) underwent facile oxidative dimerization when compared to the electron-deficient ones. Importantly, the presence of two aryl groups as well as the availability of the lone pair on the amine nitrogen are the key for the oxidative coupling reaction. Even sterically hindered substrates underwent oxidative coupling to provide excellent yields of the dimer. The above conditions offer superb functional group tolerance. No doubt, this method supersedes metal-catalyzed reactions in terms of its simplicity, economic viability, recyclability, and versatility. Currently, research efforts are in progress in our laboratories to use this method on other heterocyclic systems to arrive at functionally interesting and important molecules. In view of our present interest (metal-free approaches) in the preparation of AIEgens and novel HTMs for application in stable perovskite solar cells (PSCs) and in OLED applications, the work described and the molecules approached or designed in this report are of high relevance and importance.

■

EXPERIMENTAL SECTION

General Aspects. All reagents were used as purchased from commercial sources. All reactions were carried out in oven-dried glassware under an atmosphere of nitrogen (N2) gas and were magnetically stirred. Dichloromethane and acetonitrile were distilled over CaH2. Toluene was distilled over sodium. The reactions were monitored by thin-layer chromatography (TLC) analysis using Merck silica gel (60 F254) precoated plates (0.25 mm), and compounds were visualized under a UV chamber or using phosphomolybdic acid (PMA) solution. Column chromatography was performed on silica gel (100−200 mesh or 60−120 mesh). Melting points were measured on samples in open capillary tubes and were corrected. The infrared spectra of compounds were recorded on a JASCO FT/IR-4100 Fourier transform infrared spectrometer. 1H (400 or 500 MHz) and 13C (100 or 125 MHz) NMR spectra were obtained using a Bruker Avance 400 or 500 MHz FT-NMR spectrometer in deuterated chloroform (CDCl3) with TMS as an internal reference, unless otherwise stated. All chemical shifts are reported in parts per million (ppm, δ): 1H NMR spectra are referenced to the residual proton solvent peak (CDCl3, δ = 7.26 ppm); 13C NMR spectra are referenced to the residual proton solvent peak (CDCl3, δ = 77.16 ppm). The following abbreviations are used for the proton spectra multiplicities: s, singlet; d, doublet; t, triplet; q, quartet; qt, quintet; m, multiplet. Coupling constants (J) are reported in hertz (Hz). High-resolution mass spectra (HRMS) were recorded on a Q-Tofmicro micromass spectrometer. Spectroscopic grade solvents (i.e., dichloromethane) purchased commercially were used for recording UV−vis absorption spectra (Shimadzu UV-3100 UV−vis−NIR absorption spectrophotometer). Arylamines such as triphenylamine, 4-methyltriphenylamine, 4,4′dimethyltriphenylamine, 4-bromotriphenylamine, 4,4′-dibromotriphenylamine, 3,3′-dimethyltriphenylamine, 2-bromotriphenylamine, N,N-dimethyl-1-naphthylamine, N,N-dimethyl-2-naphthylamine, diphenylamine, 4-methyldiphenylamine, 3-methyldiphenylamine, N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, N,N-dimethylaniline were purchased from various commercial sources and were used as received. Aromatic amines, such as, 4,4′-di(t-butyl)triphenylamine,24 4-methoxytriphenylamine,25 N,N-diphenyl-1-naphthylamine,25a 4-fluorotriphenylamine,25a,26 4-cyanotriphenylamine,26 4-nitrotriphenylamine,25a,27 4-formyltriphenylamine,28 4,4′-diformyltriphenylamine,29 4-acetyltriphenylamine,30

Rf = 0.5 (19:1, hexane/EtOAc). Mp: 220−222 °C (lit.48 mp 224− 225 °C). IR (KBr, cm−1) 3029, 1590, 1490, 1326, 1275, 819. 1H NMR (400 MHz, CDCl3): δ 7.44 (d, J = 8.8 Hz, 4H), 7.25 (t, J = 8.0 Hz, 8H), 7.12 (d, J = 7.6 Hz, 8H), 7.11 (d, J = 8.8 Hz, 4H), 7.01 (t, J = 7.2 Hz, 4H). 13 C{1H} NMR (100 MHz, CDCl3): δ 147.9, 146.9, 134.9, 129.4, 127.4, 124.5, 124.2, 123.0. 8964


Article

The Journal of Organic Chemistry N,N′-Bis(4-bromophenyl)-N,N′-diphenylbenzidine, 2f.3g

Oxidative dimerization of other arylamines to afford 2−13 were performed following the typical/general procedure described previously. The reaction duration for the synthesis of dimers and characterization details of the dimers 2−13 are provided below. N,N′-Diphenyl-N,N′-bis(p-tolyl)benzidine, 2b.3f

Time: 1 min. Yield: 99 mg, >99%. Off-white solid. Rf = 0.4 (19:1, hexane/EtOAc). Mp: 153−155 °C. IR (neat, cm−1): 3069, 1592, 1582, 1486, 1314, 1277, 1073. 1H NMR (400 MHz, CDCl3): δ 7.45 (d, J = 8.4 Hz, 4H), 7.34 (d, J = 6.8 Hz, 4H), 7.27 (t, J = 7.6 Hz, 4H), 7.09−7.13 (m, 8H), 7.05 (t, J = 7.5 Hz, 2H), 6.98 (d, J = 6.8 Hz, 4H). 13C{1H} NMR (100 MHz, CDCl3): δ 147.4, 147.0, 146.5, 135.3, 132.4, 129.6, 127.6, 125.5, 124.7, 124.4, 123.5, 115.1. HR ESI-MS: [C36H26N2Br2Na]+ = [M + Na]+ calcd m/z = 667.0360, found m/z = 667.0353. N,N,N′,N′-Tetrakis(4-bromophenyl)benzidine, 2g.3g

Time: 1 min. Yield: 52 mg, >99%. Colorless solid. Rf = 0.5 (19:1, hexane/EtOAc). Mp: 163−165 °C. IR (KBr, cm−1): 3026, 2921, 1686, 1678, 1602, 1578, 1508, 1491, 1319, 1272, 1178, 1162, 1110. 1H NMR (400 MHz, CDCl3): δ 7.42 (d, J = 8.8 Hz, 4H), 7.21−7.24 (m, 4H), 7.02−7.12 (m, 16H), 6.98 (t, J = 7.4 Hz, 2H), 2.32 (s, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 148.1, 147.0, 145.3, 134.5, 133.0, 130.1, 129.3, 127.3, 125.2, 123.9, 123.7, 122.5, 21.0. N,N,N′,N ′-Tetrakis(p-tolyl)benzidine, 2c.3f,48

Time: 1 min. Yield: 49 mg, >99%. Off-white solid. Rf = 0.6 (19:1, hexane/EtOAc). Mp: 205−207 °C. IR (neat, cm−1): 2922, 1692, 1526, 1483, 1326, 1235. 1H NMR (400 MHz, CDCl3): δ 7.45 (d, J = 8.0 Hz, 4H), 7.36 (d, J = 8.4 Hz, 8H), 7.09 (d, J = 8.0 Hz, 4H), 6.98 (d, J = 8.4 Hz, 8H). 13C{1H} NMR (100 MHz, CDCl3): δ 146.5, 146.2, 135.7, 132.6, 127.8, 125.7, 124.6, 115.9. N,N′-Bis(4-fluorophenyl)-N,N′-diphenylbenzidine, 2h.51

Time: 1 min. Yield: 55 mg, >99%. White solid. Rf = 0.5 (19:1, hexane/ EtOAc). Mp: 210−212 °C (lit.46 mp 213−215 °C). IR (KBr, cm−1): 3019, 2924, 1675, 1602, 1508, 1492, 1321, 1294, 1215, 1179, 1111. 1H NMR (400 MHz, CDCl3): δ 7.40 (d, J = 8.8 Hz, 4H), 6.95−7.09 (m, 20H), 2.32 (s, 12H). 13C{1H} NMR (100 MHz, CDCl3): δ 147.2, 145.5, 134.1, 132.5, 130.0, 127.2, 124.7, 123.1, 21.0. N,N,N′,N′-Tetrakis(4-tert-butylphenyl)benzidine, 2d.

Time: 1 min. Yield: 53 mg, >99%. Gray solid. Rf = 0.2 (hexane). Mp: 185−187 °C. IR (KBr, cm−1): 3033, 2955, 2924, 1592, 1504, 1492, 1314, 1276, 1219, 1154, 1095. 1H NMR (500 MHz, CDCl3): δ 7.42 (d, J = 8.50 Hz, 4H), 7.25 (t, J = 7.75 Hz, 4H), 7.04−7.12 (m, 12H), 6.94−7.02 (m, 6H). 13C{1H} NMR (125 MHz, CDCl3): δ 159.1 (d, J = 241.56 Hz), 147.8, 146.9, 143.8 (d, J = 2.58 Hz), 134.6, 132.4, 129.4, 127.4, 126.7 (d, J = 7.91 Hz), 123.8, 123.6, 122.8, 116.2 (d, J = 22.51 Hz). HR ESI-MS: [C36H27N2F2]+ = [M + H]+ calcd m/z = 525.2142, found m/z = 525.2147. N,N′-Bis(4-cyanophenyl)-N,N′-diphenylbenzidine, 2i.

Time: 1 min. Yield: 29 mg, 35%. Dull white solid. Rf = 0.3 (hexane). Mp: 247−249 °C. IR (neat, cm−1): 2958, 2924, 1639, 1510, 1492, 1270, 1109. 1H NMR (400 MHz, CDCl3): δ 7.41 (d, J = 8.4 Hz, 4H), 7.26 (d, J = 8.8 Hz, 8H), 7.09 (d, J = 8.4 Hz, 4H), 7.05 (d, J = 8.8 Hz, 8H), 1.31 (s, 36H). 13C{1H} NMR (100 MHz, CDCl3): δ 147.1, 145.7, 145.2, 127.2, 126.1, 124.0, 123.4, 116.0, 31.6. HR ESI-MS: [C52H61N2]+ = [M + H]+ calcd m/z = 713.4835, found m/z = 713.4848. N,N′-Bis(4-methoxyphenyl)-N,N′-diphenylbenzidine, 2e.49

Time: 1 min. Yield: 96 mg, 96%. Dirty white solid. Rf = 0.2 (19:1, hexane/ EtOAc). Mp: 215−217 °C. IR (neat, cm−1): 2950, 2221, 1651, 1589, 1490, 1321, 1294. 1H NMR (400 MHz, CDCl3): δ 7.53 (d, J = 8.8 Hz, 4H), 7.44 (d, J = 8.8 Hz, 4H), 7.36 (t, J = 8.0 Hz, 4H), 7.16−7.22 (m, 10H), 7.02 (d, J = 8.8 Hz, 4H). 13C{1H} NMR (100 MHz, CDCl3): δ 151.5, 146.0, 145.4, 136.8, 133.4, 130.0, 128.1, 126.4, 126.2, 125.4, 120.3, 119.7, 103.0. HR ESI-MS: [C38H26N4Na]+ = [M + Na]+ calcd m/z = 561.2055, found m/z = 561.2064. N,N′-Bis(4-nitrophenyl)-N,N′-diphenylbenzidine, 2j.3f

Time: 3 h. Yield: 37 mg, 66%. Rf = 0.4 (19:1, hexane/EtOAc). Pale yellow solid. Mp: 156−158 °C (lit.50 mp 160 °C). IR (KBr, cm−1): 3033, 2928,1688, 1591, 1504, 1492, 1318, 1281, 1241, 1179, 1110, 1036, 909. 1H NMR (400 MHz, CDCl3): δ 7.41 (d, J = 8.4 Hz, 4H), 7.23 (t, J = 7.8 Hz, 4H), 7.04−7.14 (m, 12H), 6.96 (t, J = 7.4 Hz, 2H), 6.85 (d, J = 9.2 Hz, 4H), 3.81 (s, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 155.9, 147.8, 146.7, 140.4, 133.7, 128.9, 127.1, 126.9, 122.8, 122.6, 121.7, 114.5, 55.3. HR ESI-MS: [C38H33N2O2]+ = [M + H]+ calcd m/z = 549.2542, found m/z = 549.2529. 8965


Article


1172, 1109. 1H NMR (400 MHz, CDCl3): δ 7.93 (d, J = 8.0 Hz, 8H), 7.55 (d, J = 8.0 Hz, 4H), 7.20 (d, J = 8.0 Hz, 4H), 7.13 (d, J = 8.0 Hz, 8H), 3.89 (s, 12H). 13C{1H} NMR (100 MHz, CDCl3): δ 166.7, 151.0, 145.5, 137.0, 131.2, 128.2, 126.6, 124.5, 122.8, 52.1. HR ESI-MS: [C44H36N2O8Na]+ = [M + Na]+ calcd m/z = 743.2369, found m/z = 743.2342. N,N′-Bis(biphenyl-4-yl)-N,N′-diphenylbenzidine, 2p.52a

Time: 1 min. Yield: 55 mg, 92%. Yellow crystalline solid. Rf = 0.3 (9:1, hexane/EtOAc). Mp: 164−166 °C. IR (KBr, cm−1): 2954, 2924, 2854, 1733, 1584, 1491, 1317, 1297, 1181, 1111. 1H NMR (500 MHz, CDCl3): δ 8.06 (d, J = 9.5 Hz, 4H), 7.56 (d, J = 8.5 Hz, 4H), 7.39 (t, J = 8.0 Hz, 4H), 7.20−7.27 (m, 10H), 6.99 (d, J = 9.0 Hz, 4H). 13C{1H} NMR (125 MHz, CDCl3): δ 153.4, 145.7, 145.1, 140.5, 137.3, 130.1, 128.3, 126.7, 126.6, 126.0, 125.6, 118.7. HR ESI-MS: [C36H26N4O4Na]+ = [M + Na]+ calcd m/z = 601.1852, found m/z = 601.1821. N,N′-Bis(4-formylphenyl)-N,N′-diphenylbenzidine, 2k.3f

Time: 1 min. Yield: 63 mg, 96%. Ash-colored solid. Rf = 0.5 (19:1, hexane/EtOAc). Mp: 211−213 °C (lit.52b mp 213 °C). IR (KBr, cm−1): 3029, 1602, 1509, 1492, 1323, 1287, 1239. 1H NMR (400 MHz, CDCl3): δ 7.59 (d, J = 7.2 Hz, 4H), 7.51 (t, J = 6.8 Hz, 8H), 7.44 (t, J = 7.6 Hz, 4H), 7.32 (m, 6H), 7.19 (m, 10H), 7.07 (m, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 147.6, 147.1, 146.7, 140.7, 135.4, 135.0, 129.5, 128.9, 127.9, 127.5, 127.0, 126.8, 124.7, 124.4, 124.2, 123.2. N,N′-Bis(4-carboxyphenyl)-N,N′-diphenylbenzidine, 2q.

Time: 7 h. Yield: 55 mg, 49%. Brown solid. Rf = 0.4 (4:1, hexane/ EtOAc). Mp: 148−149 °C. IR (neat, cm−1): 3019, 2925, 2853, 2737, 1687, 1588, 1507, 1490, 1329, 1294, 1271, 1218, 1162. 1H NMR (400 MHz, CDCl3): δ 9.83 (s, 2H), 7.70 (d, J = 8.4 Hz, 4H), 7.54 (d, J = 8.4 Hz, 4H), 7.37 (t, J = 7.6 Hz, 4H), 7.19−7.25 (m, 10H), 7.08 (d, J = 8.8 Hz, 4H). 13C{1H} NMR (100 MHz, CDCl3): δ 190.6, 153.3, 146.1, 145.5, 136.8, 131.5, 129.9, 129.4, 128.1, 126.5, 126.3, 125.4, 119.8. N,N′-Bis(4-acetylphenyl)-N,N′-diphenylbenzidine, 2m.

Time: 3 h. Yield: 76 mg, 77%. Light brown solid. Rf = 0.35 (1:1, hexane/ EtOAc). Mp: 230−232 °C. IR (KBr, cm−1): 3070, 3035, 2925, 2852, 2664, 2523, 1685, 1654, 1592, 1509, 1490, 1424, 1317, 1277, 1177. 1H NMR (400 MHz, CDCl3): δ 7.91 (d, J = 8.8 Hz, 4H), 7.53 (d, J = 8.4 Hz, 4H), 7.35 (t, J = 8.0 Hz, 4H), 7.20 (m, 8H), 7.14 (t, J = 8.8 Hz, 2H), 7.05 (d, J = 8.8 Hz, 4H). 13C{1H} NMR (100 MHz, CDCl3): δ 172.0, 152.8, 146.4, 136.5, 131.9, 131.8, 130.1, 129.9, 128.0, 126.3, 126.1, 122.5, 119.9. HR ESI-MS: [C38H29N2O4]+ = [M + H]+ calcd m/z = 577.2127, found m/z = 577.2119. N,N′-Bis(4-dicyanovinylphenyl)-N,N′-diphenylbenzidine, 2r.53

Time: 7 h. Yield: 18 mg, 30%. Pale yellow solid. Rf = 0.2 (19:1, hexane/ EtOAc). Mp: 144−146 °C. IR (KBr, cm−1): 3061, 3036, 3009, 1671, 1585, 1489, 1422, 1357, 1333, 1270, 1177. 1H NMR (400 MHz, CDCl3): δ 7.82 (d, J = 8.8 Hz, 4H), 7.52 (d, J = 8.4 Hz, 4H), 7.34 (t, J = 7.8 Hz, 4H), 7.15−7.22 (m, 10H), 7.04 (d, J = 8.8 Hz, 4H), 2.53 (s, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 196.8, 152.1, 146.5, 145.8, 136.4, 130.1, 129.8, 127.9, 126.2, 126.0, 124.9, 120.2, 117.9, 26.4. HR ESI-MS: [C40H32N2O2Na]+ = [M + Na]+ calcd m/z = 595.2361, found m/z = 595.2370. N,N′-Bis(4-methoxycarbonylphenyl)-N,N′-diphenylbenzidine, 2n.3f

Time: 1 min. Yield: 54 mg, 89%. Pale brown solid. Rf = 0.4 (9:1, hexane/ EtOAc). Mp: 66 °C. IR (KBr, cm−1): 2922, 1714, 1594, 1493, 1275, 1177, 1107. 1H NMR (400 MHz, CDCl3): δ 7.88 (d, J = 8.8 Hz, 4H), 7.51 (d, J = 8.4 Hz, 4H), 7.33 (t, J = 8.0 Hz, 4H), 7.11−7.22 (m, 10H), 7.06 (d, J = 8.8 Hz, 4H), 3.88 (s, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 166.9, 151.9, 146.6, 145.9, 136.2, 131.0, 129.7, 127.8, 126.0, 125.8, 124.7, 122.5, 120.5, 51.9. N,N,N′,N′-Tetrakis(4-methoxycarbonylphenyl)benzidine, 2o.

Time: 1 h. Yield: 38 mg, 39%. Orange red solid. Rf = 0.45 (7:3, hexane/ EtOAc). Mp: 191−193 °C. IR (KBr, cm−1): 2922, 2850, 2210, 1583, 1488, 1321. 1H NMR (400 MHz, CDCl3): δ 7.51 (d, J = 8.8 Hz, 4H), 7.42 (d, J = 8.8 Hz, 4H), 7.33 (t, J = 7.6 Hz, 4H), 7.20 (d, J = 8.8 Hz, 8H), 7.16 (d, J = 8.8 Hz, 4H), 7.11 (t, J = 7.6 Hz, 2H), 6.71 (s, 2H). 13C{1H} NMR (100 MHz, CDCl3): δ 152.8, 149.6, 147.6, 147.0, 135.8, 130.4, 129.7, 129.5, 127.8, 125.6, 125.4, 124.2, 122.2 120.2. HR ESI-MS: [C44H29N6]+ = [M + H]+ calcd m/z = 641.2454, found m/z = 641.2468. N,N′-Bis(4-dibromovinylpheny l)-N,N′-diphenylbenzidine, 2s.

Time: 1 min. Yield: 65 mg, 90%. Light brown solid. Rf = 0.4 (9:1, hexane/ EtOAc). Mp: 266−268 °C. IR (KBr, cm−1): 2921, 1717, 1593, 1274, 8966


Article

The Journal of Organic Chemistry Time: 30 min. Yield: 54 mg, 55%. Green solid. Rf = 0.5 (hexane). Mp: 197−199 °C. IR (KBr, cm−1): 3033, 2355, 1594, 1492, 1321, 1176. 1H NMR (400 MHz, CDCl3): δ 7.44−7.51 (m, 8H), 7.36−7.41 (m, 4H), 7.25−7.33 (m, 3H), 7.12−7.19 (m, 6H), 6.99−7.08 (m, 7H). 13C{1H} NMR (100 MHz, CDCl3): δ 148.6, 147.5, 136.3, 136.2, 132.6, 129.7, 129.6, 127.9, 127.7, 125.3, 125.1, 124.0, 122.2, 87.2. HR ESI-MS: [C40H28N2BrK]+ = [M − 3Br + K]+ calcd m/z = 654.1073, found m/z = 654.1070. N,N′-Bis(4-dibromovinylphenyl)-N,N′-bis(4-formylphenyl)benzidine, 2t.

Time: 1 min. Yield: 57 mg, 86%. Gray solid. Rf = 0.6 (hexane). Mp: 169−171 °C. IR (KBr, cm−1): 2925, 1583, 1484, 1277, 1198, 1121. 1H NMR (400 MHz, CDCl3): δ 7.48 (d, J = 8.8 Hz, 4H), 7.29 (t, J = 8.0 Hz, 4H), 7.22−7.24 (m, 2H), 7.12 (d, J = 8.4 Hz, 8H), 7.07−7.11 (m, 6H), 6.99−7.03 (m, 2H). 13C{1H} NMR (100 MHz, CDCl3): δ 149.3, 147.2, 146.3, 135.5, 130.5, 129.6, 127.7, 126.1, 125.3, 125.0, 124.8, 123.8, 123.0, 121.9. HR ESI-MS: [C36H26N2Br2Na]+ = [M + Na]+ calcd m/z = 667.0360, found m/z = 667.0352. N,N′-Diphenyl-N,N′-bis(o-tolyl)benzidine, 2za.

Time: 1 min. Yield: 52 mg, >99%. White solid. Rf = 0.3 (hexane). Mp: 152−154 °C. IR (KBr, cm−1): 3061, 3029, 2924, 1593, 1490, 1461, 1315, 1294, 1270. 1H NMR (400 MHz, CDCl3): δ 7.40 (d, J = 8.40 Hz, 4H), 7.13−7.27 (m, 12H), 7.00 (d, J = 8.40 Hz, 8H), 6.92 (t, J = 7.20 Hz, 2H), 2.06 (s, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 147.4, 146.3, 145.4, 136.6, 133.7, 131.8, 129.7, 129.2, 127.5, 127.1, 126.2, 121.75, 121.70, 121.5, 18.7. HR ESI-MS: [C38H33N2]+ = [M + H]+ calcd m/z = 517.2644, found m/z = 517.2676. N,N′-Bis(2-bromophenyl)-N,N′-diphenylbenzidine, 2zb.

Time: 4 h. Yield: 20 mg, 43%. Yellow colored solid. Rf = 0.2 (19:1, hexane/ EtOAc). Mp: 122−124 °C. IR (KBr, cm−1): 3017, 2956, 2926, 2854, 1692, 1590, 1505, 1492, 1321, 1286. 1216, 1163, 1113, 1006. 1H NMR (400 MHz, CDCl3): δ 9.85 (s, 2H), 7.73 (d, J = 8.8 Hz, 4H), 7.59−7.52 (m, 8H), 7.44 (s, 2H), 7.22 (d, J = 8.4 Hz, 4H), 7.1−7.19 (m, 8H). 13C{1H} NMR (100 MHz, CDCl3): δ 190.6, 152.7, 146.4, 145.3, 137.1, 136.0, 131.5, 130.2, 129.9, 128.3, 126.6, 125.0, 123.1, 121.1, 89.0. HR ESI-MS: [C42H29N2O2]+ = [M − 4Br + H]+ calcd m/z = 593.2229, found m/z = 593.2202. N,N,N′,N′-Tetrakis(4-dibromovinylphenyl)benzidine, 2u.

Time: 1 min. Yield: 263 mg, >99%. White solid. Rf = 0.4 (19:1, hexane: EtOAc). Mp: 162−164 °C. IR (KBr, cm−1): 3059, 3032, 3007, 2923, 2853, 1592, 1491, 1470, 1315, 1293, 1028. 1H NMR (500 MHz, CDCl3): δ 7.65 (dd, J = 1.40 and 8.00 Hz, 2H), 7.43 (d, J = 8.50 Hz, 4H), 7.33 (dt, J = 1.40 and 8.00 Hz, 2H), 7.21−7.29 (m, 6H), 7.12 (dt, J = 1.40 and 8.00 Hz, 2H), 6.97−7.03 (m, 10H). 13C{1H} NMR (125 MHz, CDCl3): δ 147.0, 145.9, 145.5, 134.7, 134.3, 131.8, 129.2, 129.0, 127.5, 127.2, 123.9, 122.24, 122.19, 111.8. HR ESI-MS: [C36H26N2Br2Na]+ = [M + Na]+ calcd m/z = 667.0360, found m/z = 667.0345. N,N′-Bis(2-nitrophenyl)-N,N′-diphenylbenzidine, 2zc.

Time: 1 min. Yield: 55 mg, 89%. Yellow solid. Rf = 0.4 (19:1, hexane/ EtOAc). Mp: 121−123 °C. IR (KBr, cm−1): 3017, 2956, 2926, 2884, 2855, 1686, 1597, 1504, 1402, 1322, 1303, 1281, 1215, 1183, 1072, 1009. 1H NMR (400 MHz, CDCl3): δ 7.45−7.53 (m, 12H), 7.37−7.42 (m, 6H), 7.09 (m, 6H), 7.03 (d, J = 8.4 Hz, 4H). 13C{1H} NMR (100 MHz, CDCl3): δ 147.3, 147.0, 136.2, 132.7, 129.8, 129.7, 127.9, 125.7, 123.3, 87.9. HR ESI-MS: [C44H28N2Br3K]+ = [M − 5Br + K]+ calcd m/z = 859.9440, found m/z = 859.9450. 2,2′-Dimethyl-N,N,N′,N′-tetrakis(p-tolyl)benzidine, 2x.54

Time: 1 min. Yield: 59 mg, >99%. Yellow solid. Rf = 0.2 (19:1, hexane/ EtOAc). Mp: 148−150 °C. IR (KBr, cm−1): 3062, 3032, 2924, 1723, 1594, 1525, 1491, 1350, 1316, 1276, 1177, 1158. 1H NMR (400 MHz, CDCl3): δ 7.80 (dd, J = 1.30 and 8.2 Hz, 2H), 7.50 (dt, J = 1.30 and 8.20 Hz, 2H), 7.42 (d, J = 8.4 Hz, 4H), 7.31 (dd, J = 1.30 and 8.2 Hz, 2H), 7.25 (t, J = 8.0 Hz, 4H), 7.19 (t, J = 7.2 Hz, 2H), 7.11 (t, J = 8.4 Hz, 2H), 7.04 (d, J = 8.4 Hz, 8H). 13C{1H} NMR (100 MHz, CDCl3): δ 146.4, 145.7, 145.6, 141.1, 135.5, 133.7, 130.0, 129.5, 127.6, 126.2, 124.4, 123.8, 123.4, 123.3. HR ESI-MS: [C36H26N4O4Na]+ = [M + Na]+ calcd m/z = 601.1852, found m/z = 601.1871. N,N′-Bis(2-cyanophenyl)-N,N′-diphenylbenzidine, 2zd.

Time: 1 min. Yield: 48 mg, 82%. White solid. Rf = 0.3 (hexane). Mp: 150 °C (lit.54 mp 248−250 °C). 1H NMR (400 MHz, CDCl3): δ 7.08 (d, J = 8.0 Hz, 8H), 7.04 (d, J = 8.0 Hz, 8H), 6.93−6.99 (m, 4H), 6.86 (d, J = 8.4 Hz, 2H), 2.33 (s, 12H), 2.00 (s, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 146.9, 145.7, 137.0, 135.2, 132.2, 130.4, 129.9, 124.6, 123.9, 120.1, 21.0, 20.2. IR (KBr, cm−1): 2922, 2854, 1654, 1647, 1637, 1627, 1617, 1602, 1508, 1482, 1321, 1295, 1274. HR ESI-MS: [C42H41N2]+ = [M + H]+ calcd m/z = 573.3270, found m/z = 573.3274. N,N′-Bis(3-bromophenyl)-N,N′-diphenylbenzidine, 2y.

Time: 1 min. Yield: 55 mg, >99%. Light gray solid. Rf = 0.3 (9:1, hexane/ EtOAc). Mp: 201−204 °C. IR (KBr, cm−1): 3061, 3034, 2956, 2926, 2226, 1940, 1733, 1587, 1483, 1444, 1271, 1159, 1077, 1027. 1H NMR (400 MHz, CDCl3): δ 7.59 (d, J = 7.6 Hz, 2H), 7.44−7.52 (m, 6H), 7.30 (t, J = 7.2 Hz, 4H), 7.22 (d, J = 8.4 Hz, 2H), 7.15 (t, J = 7.6 Hz, 2H), 7.02−7.11 (m, 10H). 13C{1H} NMR (100 MHz, CDCl3): δ 150.7, 8967


Article


of 2w/3c/3d (0.35:1.0:1.34) was arrived at from the integrations of the methyl signals in the 1H NMR spectrum (for details, see the SI, Figure S22). Time: 1 min. Conversion: 100%. Rf = 0.3 (hexanes). 1H NMR (400 MHz, CDCl3): δ 7.24−7.31 (unresolved, 6H), 7.18−7.24 (unresolved, 8H), 7.04−7.18 (unresolved, 25H), 6.89−7.04 (unresolved, 27H), 6.80−6.89 (m, 10H), 2.28 (s, 22H), 2.26 (s, 4H), 2.24 (s, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 148.0, 147.9, 146.7, 143.0, 140.0, 139.4, 139.2, 136.4, 136.1, 136.0, 135.5, 132.9, 130.7, 130.1, 129.3, 129.1, 125.8, 125.4, 125.3, 125.2, 124.2, 124.1, 123.8, 123.1, 122.5, 121.8, 121.8, 121.6, 114.2, 22.8, 21.6, 21.0, 20.3. HR ESI-MS: [C40H37N2]+ = [M + H]+ calcd m/z = 545.2957, found m/z = 545.2971. Preparation of Novel Naphthylalkylbenzidines or Tetraarylnaphthidines. Inseparable Mixture of N,N,N′,N′-Tetraphenylnaphthidine, 5a, and N,N′-Bis(naphthalene-1-yl)-N,N′-diphenylbenzidine, 6a.

147.1, 146.3, 135.7, 134.9, 133.9, 129.6, 127.8, 127.7, 124.2, 124.2, 124.1, 124.0, 117.1, 109.9. HR ESI-MS: [C38H26N4Na]+ = [M + Na]+ calcd m/z = 561.2055, found m/z = 561.2007. Oxidative Coupling of 3-Methyltriphenylamine.

Time: 1 min. Yield: 55% (6a)55 and 45% (5a) by 1H NMR (conversion 100%). White solids. Rf = 0.3 (19:1, hexane/EtOAc). IR (KBr, cm−1): 3060, 3034, 3008, 2955, 2924, 2854, 1734, 1590, 1492, 1459, 1389, 1308, 1293, 1274, 1215, 1077, 1027. 1H NMR (400 MHz, CDCl3): δ 8.02 (t, J = 8.40 Hz, 2H), 7.91 (d, J = 8.4 Hz, 1H), 7.80 (d, J = 8.4 Hz, 1H), 7.30−7.55 (m, 11H), 7.10−7.27 (m, 10H), 7.06 (d, J = 7.6 Hz, 4H), 6.89−6.99 (m, 3H). 13C{1H} NMR (100 MHz, CDCl3): δ 148.6, 148.3, 147.8, 143.5, 142.7, 138.6, 135.5, 133.6, 133.5, 131.6, 131.5, 131.0, 129.3, 129.2, 128.6, 127.6, 127.5, 127.0, 126.9, 126.8, 126.64, 126.56, 126.35, 126.28, 126.1, 124.6, 124.4, 122.3, 122.1, 122.0, 121.7, 121.2. HR ESI-MS: [C44H33N2]+ = [M + H]+ calcd m/z = 589.2644, found m/z = 589.2642. N,N,N′,N′-Tetrakis(4-tert-butylphenyl)diphenylnaphthidine, 5b.

Oxidative coupling of 3-methyltriphenylamine resulted in an inseparable mixture of three products, 2v, 3a,54 and 3b, and the relative ratio of 2v/3a/3b (0.3:1.0:1.6) was arrived at from the integrations of the methyl signals in the 1H NMR spectrum (for details, see the SI, Figure S21). Time: 1 min. Conversion: 100%. Rf = 0.3 (hexanes). 1 H NMR (400 MHz, CDCl3): δ 7.46 (d, J = 8.4 Hz, 3H), 7.26 (t, J = 8.4 Hz, 18H), 7.20 (d, J = 8.8 Hz, 5H), 7.06−7.18 (m, 30H), 7.01 (t, J = 7.2 Hz, 8H), 6.90−6.99 (m, 12H), 6.85 (d, J = 7.2 Hz, 3H), 2.28 (s, 6H), 2.27 (s, 5H), 2.23 (s, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 148.4, 148.02, 147.99, 147.8, 147.7, 146.95, 146.92, 146.6, 146.5, 139.2, 136.4, 136.2, 135.6, 134.7, 132.2, 131.6, 131.0, 130.7, 130.1, 129.7, 129.3, 129.2, 128.3, 127.4, 125.8, 125.3, 124.4, 124.3, 124.2, 123.9, 123.8, 123.2, 122.74, 122.71, 121.9, 121.7, 21.6, 21.0. HR ESI-MS: [C38H33N2]+ = [M + H]+ calcd m/z = 517.2644, found m/z = 517.2634. Oxidative Coupling of 3,3′-Dimethyltriphenylamine.

Time: 1 min. Yield: 47 mg, 47%. Brown solid. Rf = 0.5 (19:1, hexane/ EtOAc). Mp: 117−119 °C. IR (KBr, cm−1): 3020, 1639, 1510, 1492, 1270, 1109. 1H NMR (400 MHz, CDCl3): δ 8.11 (d, J = 8.0 Hz, 2H), 7.50 (m, 4H), 7.46 (d, J = 8.0 Hz, 2H), 7.36 (t, J = 7.2 Hz, 2H), 7.29 (t, J = 7.2 Hz, 2H), 7.25 (d, J = 8.8 Hz, 8H), 7.05(d, J = 8.8 Hz, 8H), 1.31 (s, 36H). 13C{1H} NMR (100 MHz, CDCl3): δ 146.2, 144.3, 143.8, 136.6, 134.7, 131.7, 128.7, 127.3, 126.8, 126.25, 126.24, 126.0, 124.9, 121.4, 34.3, 31.6. HR ESI-MS: [C60H65N2]+ = [M + H]+ calcd m/z = 813.5148, found m/z = 813.5132. Preparation of Arylalkylbenzidines via an Oxidative Coupling Method. N,N′-Diethyl-N,N′-diphenylbenzidine, 8a.

Time: 24 h. Yield: 95 mg, 59%. Brown oil. Rf = 0.2 (hexane). IR (neat, cm−1): 3032, 2955, 2925, 1593, 1496, 1464, 1365, 1251, 1219. 1H NMR (400 MHz, CDCl3): δ 7.49 (d, J = 8.0 Hz, 4H), 7.30 (t, J = 7.6 Hz, 4H), 7.05 (m, 8H), 6.98 (t, J = 7.2 Hz, 2H), 3.73 (q, J = 7.2 Hz, 4H), 1.29 (t, J = 7.2 Hz, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 148.1, 146.9, 133.5, 129.4, 127.3, 121.4, 120.8, 52.5, 22.8.

Oxidative coupling of 3,3′-dimethyltriphenylamine resulted in an inseparable mixture of three products 2w,48 3c, and 3d, and the relative ratio 8968


Article

The Journal of Organic Chemistry N,N′-Diethyl-N,N′-bis(naphthalen-1-yl)benzidine, 10a.

N,N′-Dihexyl-N,N′-diphenylbenzidine, 8b.

Time: 24 h. Yield: 142 mg, 69%. Brown oil. Rf = 0.3 (hexane). IR (neat, cm−1): 3423, 3010, 2956, 2928, 1593, 1495, 1364, 1249, 1216, 1187, 1140, 1087. 1H NMR (400 MHz, CDCl3): δ 7.46 (d, J = 8.4 Hz, 4H), 7.27 (t, J = 7.2 Hz, 4H), 6.98−7.08 (m, 8H), 6.95 (t, J = 7.2 Hz, 2H), 3.71 (t, J = 7.6 Hz, 4H), 1.63−1.74 (m, 4H), 1.29 (m, 12H), 0.9 (m, 6H). 13 C{1H} NMR (100 MHz, CDCl3): δ 148.1, 147.0, 133.5, 129.4, 127.3, 121.4, 120.8, 117.9, 52.5, 31.8, 27.6, 26.9, 22.8, 14.2. HR ESI-MS: [C36H44N2K]+ = [M + K]+ calcd m/z = 543.3142, found m/z = 543.3122. N,N′-Dibenzyl-N,N′-diphenylbenzidine, 8c.

Time: 6 h. Yield: 174 mg, 87%. Brown oily liquid. Rf = 0.4 (9:1, hexane/ EtOAc). IR (neat, cm−1): 3046, 3033, 3007, 2967, 1610, 1593, 1573, 1498, 1464, 1396, 1372, 1345, 1267, 1215, 1179, 1138, 1075, 1012. 1 H NMR (400 MHz, CDCl3): δ 7.92 (d, J = 8.0 Hz, 4H), 7.82 (d, J = 8.0 Hz, 2H), 7.48−7.57 (m, 4H), 7.38−7.47 (m, 4H), 7.31 (d, J = 8.4 Hz, 4H), 6.60 (d, J = 8.4 Hz, 4H), 3.85(q, J = 6.80 Hz, 4H), 1.29 (t, J = 6.80 Hz, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 147.8, 143.5, 135.3, 132.0, 130.0, 128.5, 127.0, 126.9, 126.5, 126.3, 124.0, 113.5, 46.6, 13.2. HR ESI-MS: [C36H32N2Na]+ = [M + Na]+ calcd m/z = 515.2463, found m/z = 515.2440. N,N′-Diethyl-N,N′-bis(naphthalen-2-yl)benzidine, 10b.

Time: 24 h. Yield: 65 mg, 62%. White solid. Rf = 0.4 (hexane). Mp: 233−235 °C. IR (KBr, cm−1): 3029, 2955, 1691, 1594, 1496, 1316, 1222, 1176. 1H NMR (400 MHz, CDCl3): δ 7.30 (d, J = 8.0 Hz, 4H), 7.25 (d, J = 7.6 Hz, 4H), 7.23−7.08 (m, 12 H), 7.01 (d, J = 8.0 Hz, 4H), 6.84 (t, J = 7.2 Hz, 2H). 13C{1H} NMR (100 MHz, CDCl3): δ 148.0, 146.9, 139.3, 133.7, 129.4, 128.7, 127.3, 126.9, 126.6, 121.7, 121.1, 120.6, 56.4. HR ESI-MS: [C38H33N2]+ = [M + H]+ calcd m/z = 517.2644, found m/z = 517.2629. N,N′-Diethyl-2,2′-dimethoxy-N,N′-diphenylbenzine, 8d.

Time: 2 h. Yield: 60 mg, 60%. Brown oil. Rf = 0.4 (19:1, hexane/EtOAc). IR (neat, cm−1): 3058, 3011, 2958, 2925, 1628, 1592, 1494, 1470, 1377, 1263, 1216, 1135, 1121, 1091. 1H NMR (400 MHz, CDCl3): δ 7.65 (d, J = 8.4 Hz, 2H), 7.59 (d, J = 9.2 Hz, 4H), 7.33 (t, J = 7.2 Hz, 2H), 7.15−7.27 (m, 6H), 7.10 (dd, J = 9.0 and 2.0 Hz, 2H), 6.99 (d, J = 8.0 Hz, 4H), 6.92 (t, J = 7.2 Hz, 2H), 3.82 (q, J = 7.2 Hz, 4H), 1.20 (t, J = 7.2 Hz, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 147.8, 145.4, 134.8, 129.4, 129.2, 128.8, 127.6, 126.8, 126.3, 123.8, 122.5, 121.8, 115.3, 46.8, 22.8. HR ESI-MS: [C36H33N2]+ = [M + H]+ calcd m/z = 493.2644, found m/ z = 493.2656. Preparation of Novel N,N′-Diarylbenzidines or N,N′-Diarylnaphthidines. N,N′-Diphenylbenzidine, 12a.56a

Time: 9 h. Yield: 29 mg, 35%. Brown liquid. Rf = 0.2 (19:1, hexane/ EtOAc). IR (neat, cm−1): 2965, 2927, 1592, 1493, 1461, 1373, 1262, 1212, 1126, 1038. 1H NMR (400 MHz, CDCl3): δ 7.30 (t, J = 8.0 Hz, 4H), 7.17 (d, J = 8.4 Hz, 2H), 7.09 (d, J = 8.0 Hz, 4H), 6.97 (t, J = 7.2 Hz, 2H), 6.57−6.66 (m, 4H), 3.83 (q, J = 7.2 Hz, 4H), 3.69 (s, 6H), 1.27 (t, J = 7.2 Hz, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 157.9, 148.0, 147.7, 132.3, 129.4, 121.6, 121.4, 120.5, 112.3, 104.2, 55.8, 46.7, 13.0. HR ESI-MS: [C30H33N2O2]+ = [M + H]+ calcd m/z = 453.2542, found m/z = 453.2541. N,N′-Diphenyl-6,6′-bis(tetrahydroquinoline), 8e.

Time: 24 h. Yield: 52 mg, 38%. Brown solid. Rf = 0.65 (7:3, hexane/ EtOAc). Mp: 238−240 °C (lit.56b mp 239−242 °C). IR (KBr, cm−1): 3388, 2960, 2927, 1639, 1596, 1507, 1318. 1H NMR (500 MHz, CDCl3): δ 7.48 (d, J = 9.0 Hz, 4H), 7.28 (t, J = 8.5 Hz, 4H), 7.13 (d, J = 8.8 Hz, 4H), 7.10 (d, J = 8.5 Hz, 4H), 6.94 (t, J = 7.5 Hz, 2H). 13C{1H} NMR (100 MHz, CDCl3): δ 143.4, 140.9, 129.5, 127.5, 121.1, 119.1, 118.2, 117.9. HR ESI-MS: [C24H21N2]+ = [M + H]+ calcd m/z = 337.1705, found m/z = 337.1736. N,N′-Bis(p-tolyl)benzidine, 12b.

Time: 12 h. Yield: 31 mg, 61%. Brown solid. Rf = 0.5 (hexane). Mp: 148−150 °C. IR (neat, cm−1): 3061, 3035, 1582, 1560, 1492, 1473, 1332, 1276, 1168, 1072. 1H NMR (400 MHz, CDCl3): δ 7.37 (t, J = 7.2 Hz, 4H), 7.25−7.30 (m, 6H), 7.07−7.17 (m, 4H), 6.82 (d, J = 8.8 Hz, 2H), 3.67 (t, J = 5.6 Hz, 4H), 2.92 (t, J = 6.4 Hz, 4H), 2.09 (qt, J = 6.0 Hz, 4H). 13C{1H} NMR (100 MHz, CDCl3): δ 148.5, 143.0, 131.6, 129.5, 127.3, 124.9, 124.6, 124.5, 123.5, 116.3, 51.0, 28.0, 23.0. HR ESI-MS: [C30H29N2]+ = [M + H]+ calcd m/z = 417.2331, found m/ z = 417.2336.

Time: 30 min. Yield: 58 mg, 80%. Brown solid. Rf = 0.65 (7:3, hexane/ EtOAc). Mp: 271−273 °C. IR (KBr, cm−1): 3207, 3019, 1690, 1518, 1416, 1215, 1113. 1H NMR (400 MHz, CDCl3): δ 7.44 (d, J = 8.4 Hz, 4H), 7.09 (d, J = 8.4 Hz, 4H), 7.06 (d, J = 8.4 Hz, 4H), 7.02 (d, J = 8.4 Hz, 4H), 5.72 (bs, 2H), 2.31 (s, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 143.2, 142.0, 133.7, 129.5, 127.5, 121.1, 118.2, 117.9, 22.8. HR ESI-MS: [C26H25N2]+ = [M + H]+ calcd m/z = 365.2018, found m/z = 365.1984. 8969


Article

The Journal of Organic Chemistry N,N′-Bis(m-tolyl)benzidine, 12c.

portionwise under nitrogen gas atmosphere. The whole of the solution turned orange. After the reaction mixture was stirred for 5 min, compound 2k (170 mg, 0.31 mmol) was added into the reaction flask under nitrogen gas atmosphere, and the contents were stirred further for 36 h. After this time, the reaction was quenched with water (2.0 mL), and THF was removed at the vacuo. The organic contents were then extracted into chloroform (3 × 10 mL). The combined organic layer was washed with brine, dried over anhyd sodium sulfate, filtered, and evaporated to dryness to afford a crude solid, which was then purified by silica gel column chromatography using hexane-ethyl acetate mixtures to offer 14. Yield: 48 mg, 29%. Orange solid. Rf = 0.3 (19:1, hexane/ EtOAc). Mp: 202−204 °C. IR (KBr, cm−1): 3033, 2926, 2847, 2724, 1688, 1495, 1195. 1H NMR (400 MHz, CDCl3): δ 7.44 (d, J = 8.4 Hz, 4H), 7.30 (d, J = 8.4 Hz, 4H), 7.25 (d, J = 6.8 Hz, 4H), 7.12 (d, J = 7.6 Hz, 8H), 7.01−7.09 (m, 6H), 6.66 (dd, J = 10.8 and 16.6 Hz, 2H), 5.64 (d, J = 16.6 Hz, 2H), 5.16 (d, J = 10.8 Hz, 2H). 13C{1H} NMR (100 MHz, CDCl3): δ 147.6, 147.5, 146.6, 136.3, 135.0, 132.1, 129.4, 127.5, 127.2, 124.6, 124.4, 123.9, 123.2, 112.4. N,N′-Bis(4-styrylphenyl)-N,N′-(diphenyl)benzidine, 15.60

Time: 3 h. Yield: 58 mg, 39%. Brown solid. Rf = 0.2 (9:1, hexane/ EtOAc). Mp: 227−229 °C. IR (KBr, cm−1): 3288, 3020, 1525, 1478, 1424, 1215. 1H NMR (400 MHz, CDCl3): δ 7.28 (t, J = 8.4 Hz, 4H), 7.11 (dd, J = 8.59 and 1.03 Hz, 4H), 7.00 (m, 4H), 6.93 (m, 4H), 5.72 (bs, 2H), 2.05 (s, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 143.4, 142.0, 137.6, 134.5, 130.8, 129.5, 120.9, 119.1, 117.9, 115.1, 20.3. HR ESI-MS: [C26H25N2]+ = [M + H]+ calcd m/z = 365.2018, found m/ z = 365.2021. N,N′-Diphenylnaphthidine, 12d.15a,57

Time: 1 min. Yield: 153 mg, 86%. Brown solid. Rf = 0.65 (7:3, hexane/ EtOAc). Mp: 228−230 °C (lit.56b mp 181−182 °C). IR (KBr, cm−1): 3386, 3045, 3011, 1600, 1584, 1519, 1498, 1455, 1377, 1305, 1255, 1215, 1177, 1156, 1052, 1027. 1H NMR (500 MHz, CDCl3): δ 8.14 (d, J = 8.0 Hz, 2H), 7.45−7.54 (m, 6H), 7.42 (d, J = 7.5 Hz, 2H), 7.29−7.36 (m, 6H), 7.12 (d, J = 7.5 Hz, 4H), 6.96 (t, J = 7.00 Hz, 2H), 6.07 (bs, 2H). 13C{1H} NMR (100 MHz, CDCl3): δ 144.8, 138.7, 134.2, 129.5, 128.4, 127.7, 127.5, 126.2, 125.7, 122.0, 120.7, 117.7, 115.3. HR ESI-MS: [C32H25N2]+ = [M + H]+ calcd m/z = 437.2018, found m/z = 437.2040. N,N′-Bis(2-naphthyl)benzidine, 12e.57

To a solution of diethyl benzylphosphonate (503 mg, 2.20 mmol) in THF (30.0 mL) was introduced t-BuOK (371 mg, 3.31 mmol) portionwise under nitrogen gas atmosphere. The whole of the solution turned red to brown in color. After the reaction mixture was stirred for 5 min, compound 2k (300 mg, 0.55 mmol) was added into the reaction flask under nitrogen gas atmosphere, and the contents were stirred further for 5 h. After this time, the reaction was quenched with water (10.0 mL), and THF was removed at the vacuo. The organic contents were then extracted into chloroform (3 × 25 mL). The combined organic layer was washed with brine, dried over anhyd sodium sulfate, filtered, and evaporated to dryness to afford a crude solid, which was then purified by silica gel column chromatography using hexane−ethyl acetate mixtures to offer compound 15. Yield: 324 mg, 85%. Yellowish solid. Rf = 0.4 (19:1, hexane/EtOAc). Mp: 207−209 °C. IR (KBr, cm−1): 3029, 2911, 2847, 1591, 1496, 1321, 959. 1H NMR (400 MHz, CDCl3): δ 7.49 (t, J = 8.4 Hz, 8H), 7.41 (d, J = 8.8 Hz, 4H), 7.35 (t, J = 7.8 Hz, 4H), 7.32−7.12 (m, 6H), 7.16 (d, J = 8.0 Hz, 8H), 7.12−7.01 (m, 10H). 13C{1H} NMR (100 MHz, CDCl3): δ 147.5, 147.3, 146.6, 137.7, 135.1, 131.8, 129.5, 128.8, 128.3, 127.5, 127.4, 127.3, 126.4, 124.7, 124.5, 123.9, 123.3. Preparation of New Arylamines. Other than the arylamines mentioned earlier, a few novel arylalkylamines, such as N-ethyl-Nphenyl-2-naphthylamine, N-ethyl-3-methoxydiphenylamine, and N-(4formylphenyl)-N-(4′-dibromovinylidenylphenyl)aniline, were synthesized in our laboratory for the study, and the experimental details as well as their characterization details are provided below. N-Ethyl-N-phenylnaphthalen-2-amine.

Time: 1 min. Yield: 136 mg, 77%. Brown solid. Rf = 0.65 (7:3, hexane/ EtOAc). Mp: 224−226 °C. IR (KBr, cm−1): 3402, 3019, 2956, 1727, 1610, 1511, 1461, 1215, 1180. 1H NMR (400 MHz, CDCl3): δ 7.85−7.91 (m, 4H), 7.72−7.78 (m, 5H), 7.40−7.43 (m, 5H), 7.19 (d, J = 8.4 Hz, 4H), 7.01 (d, J = 8.4 Hz, 4H). 13C{1H} NMR (100 MHz, CDCl3): δ 145.3, 137.2, 133.9, 131.9, 130.4, 129.3, 128.3, 128.1, 127.4, 126.4, 125.7, 124.3, 122.1, 115.6. HR ESI-MS: [C32H25N2]+ = [M + H]+ calcd m/z = 437.2018, found m/z = 437.2010. N,N′-Diethylnaphthidine, 13a.58

Time: 3 h. Yield: 36 mg, 21%. Brown solid. Rf = 0.4 (9:1, hexane/ EtOAc). Mp: 156−158 °C. IR (neat, cm−1): 3328, 3019, 2921, 1705, 1635, 1461, 1364, 1217, 1082. 1H NMR (400 MHz, CDCl3): δ 7.83−7.87 (m, 2H), 7.43−7.48 (m, 4H), 7.33−7.37 (m, 2H), 7.20 (d, J = 8.0 Hz, 2H), 6.65 (d, J = 8.0 Hz, 2H), 3.38 (q, J = 7.2 Hz, 4H), 1.43 (t, J = 7.2 Hz, 6H). 13C{1H} NMR (100 MHz, CDCl3): δ 145.9, 144.5, 131.2, 130.0, 126.9, 125.8, 125.1, 122.8, 120.6, 116.7, 103.0, 38.6, 14.8. Metal-Free Synthesis of Fluorescent Hole-Transporting Materials. N,N′-Bis(4-vinylphenyl)-N,N′-(diphenyl)benzidine, 14.59

To a solution of N-phenylnaphthylamine (500 mg, 2.3 mmol) in DMSO (10.0 mL) were introduced NaOH (455 mg, 11.4 mmol) and ethyl iodide (0.36 mL, 4.6 mmol), and the contents were allowed to stirr at 80 °C for 21 h. After a regular workup, the organic contents extracted into hexane was dried under reduced pressure to afford a crude oil which was further purified by short-pad silica gel column chromatography (hexanes) to provide an oily liquid. Yield: 568 mg, 95%. Brown oil. Rf = 0.7 (19:1, hexane/EtOAc). IR (KBr, cm−1): 3055, 2971, 2929, 1628, 1592, 1493, 1470, 1377, 1252, 1224, 1120, 957. 1H NMR (500 MHz, CDCl3): δ 7.74 (d, J = 8.0 Hz, 1H), 7.69 (dd, J = 9.0 and 2.0 Hz, 2H),

To a solution of triphenylmethylphosphonium bromide (228 mg, 0.64 mmol) in THF (2.0 mL) was introduced t-BuOK (72 mg, 0.64 mmol) 8970


Article

The Journal of Organic Chemistry 7.42 (t, J = 7.0 Hz, 1H), 7.37 (d, J = 2.0 Hz, 1H), 7.27−7.35 (m, 3H), 7.20 (dd, J = 9.0 and 2.5 Hz, 1H), 7.10 (d, J = 8.0 Hz, 2H), 7.01 (t, J = 7.5 Hz, 1H), 3.92 (q, J = 7.0 Hz, 2H), 1.30 (t, J = 7.0 Hz, 3H). 13C{1H} NMR (100 MHz, CDCl3): δ 147.8, 145.4, 134.8, 129.4, 129.2, 128.8, 127.6, 126.8, 126.3, 123.7, 122.4, 121.7, 115.3, 46.8, 12.8. HR ESI-MS: [C18H18N]+ = [M + H]+ calcd m/z = 248.1439, found m/z = 248.1438. N-Ethyl-3-methoxydiphenylamine.61

■

electrochemical data, and single-crystal X-ray diffraction data of 2h/2zd along with their ORTEP drawings (PDF) X-ray crystallographic data for compound 2h (CCDC 1550109) (CIF) X-ray crystallographic data for compound 2zd (CCDC 1550108) (CIF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected].

To a solution of 3-methoxydiphenylamine (500 mg, 2.51 mmol) in DMF (10.0 mL) was introduced anhydrous K2CO3 (522 mg, 3.77 mmol), and the mixture was stirred at room temperature. After that, ethyl iodide (0.3 mL, 3.77 mmol) was introduced under ice-cold conditions. The whole of the contents was stirred further at room temperature for 6 h. After regular workup, the organic contents extracted into ethyl acetate were dried under reduced pressure to afford a crude oil which was then purified by a short-pad silica gel column chromatography (hexanes) to provide an oily liquid. Yield: 442 mg, 78%. Pale brown oil. Rf = 0.3 (hexanes). IR (neat, cm−1): 3060, 2971, 2935, 1613, 1491, 1373, 1249, 1207, 1168, 1127, 1100, 1047. 1H NMR (400 MHz, CDCl3): δ 7.30 (t, J = 8.0 Hz, 2H), 7.16 (t, J = 8.0 Hz, 1H), 7.06 (d, J = 8.0 Hz, 2H), 7.00 (t, J = 8.0 Hz, 1H), 6.47−6.57 (m, 3H), 3.81−3.75 (m, 5H), 1.24 (t, J = 7.0 Hz, 3H). 13C{1H} NMR (100 MHz, CDCl3): δ 160.7, 149.3, 147.6, 129.9, 129.3, 122.39, 122.0, 112.7, 106.0, 105.7, 55.3, 46.6, 12.9. HR ESIMS: [C15H18NO]+ = [M + H]+ calcd m/z = 228.1388, found m/z = 228.1378. N-(4-Formylphenyl)-N-(4′-dibromovinylidenylphenyl)aniline.

ORCID

Parthasarathy Venkatakrishnan: 0000-0002-0895-2861 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS P.V.K is grateful to DST-SERB SB/S1/OC-47/2014, CSIR 02(0185)/13/EMRII, New Delhi, India, for funding. Sudhakar thanks CSIR for a SRF and Sudesh thanks IITM for a SRF fellowship. The Department of Chemistry, IIT Madras, is acknowledged for allowing us to use the facilities. Mr. Ramkumar, Department of Chemistry, IIT Madras, is acknowledged for help with the X-ray structures.

■

4,4′-Diformyltriphenylamine (250 mg, 0.83 mmol) was heated in toluene in the presence of the Corey−Fuchs reagent consisting of a mixture of CBr4 (1200 mg, 3.73 mmol) and PPh3 (1740 mg, 6.64 mmol) for a period of 6 h. After a regular workup, the organic contents extracted into ethyl acetate were evaporated to dryness under reduced pressure. The crude product thus obtained was purified by short pad silica gel column chromatography to afford the desired product N-(4-formylphenyl)-N-(4′-dibromovinylidenylphenyl)aniline (121 mg, 32%) in addition to the side product N,N-bis(4,4′-dibromovinylidenylphenyl)aniline (285 mg, 56%), which was isolated and characterized to match with the previous reports.47 The characterization details of N-(4-formylphenyl)N-(4′-dibromovinylidenylphenyl)aniline follow. Yellow solid. Rf = 0.4 (9:1, hexane/EtOAc). Mp: 75−77 °C. IR (KBr, cm−1): 3029, 2911, 2847, 1594, 1492, 1321, 1176. 1H NMR (400 MHz, CDCl3): δ 9.83 (s, 1H), 7.70 (d, J = 8.8 Hz, 2H), 7.52 (d, J = 8.4 Hz, 2H), 7.43 (s, 1H), 7.36 (t, J = 8.0 Hz, 2H), 7.22−7.15 (m, 3H), 7.12 (d, J = 8.8 Hz, 2H), 7.07 (d, J = 8.8 Hz, 2H). 13C{1H} NMR (100 MHz, CDCl3): δ 190.6, 152.9, 146.5, 146.0, 136.0, 131.5, 131.2, 130.04, 129.98, 129.86, 126.7, 125.7, 124.9, 120.7, 88.9. HR ESI-MS: [C21H15NOBr2Na]+ = [M + Na]+ calcd m/z = 477.9418, found m/z = 477.9414.

■

REFERENCES

(1) (a) Su, S.; Herron, N.; Meng, H. In Organic Light-Emitting Materials and Devices; Li, Z. R., Ed.; CRC Press, Taylor & Francis Group, Boca Raton, 2015; Chapter 3, p 309. (b) Wang, J.; Liu, K.; Ma, L.; Zhan, X. Chem. Rev. 2016, 116, 14675−14725. (c) Calió, L.; Kazim, S.; Grätzel, M.; Ahmad, S. Angew. Chem., Int. Ed. 2016, 55, 14522−14545. (d) Thomas, S. W., III; Joly, G. D.; Swager, T. M. Chem. Rev. 2007, 107, 1339−1386. (e) Carter, K. P.; Young, A. M.; Palmer, A. E. Chem. Rev. 2014, 114, 4564−4601. (2) (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457−2483. (b) Carsten, B.; He, F.; Son, H. J.; Xu, T.; Yu, L. Chem. Rev. 2011, 111, 1493−1528. (c) Guan, B.-T.; Lu, X.-Y.; Zheng, Y.; Yu, D.-G.; Wu, T.; Li, K.-L.; Li, B.-J.; Shi, Z.-J. Org. Lett. 2010, 12, 396−399 and references cited therein. (d) Lin, H.; Sun, D. Org. Prep. Proced. Int. 2013, 45, 341. (e) Copper-Mediated Cross-Coupling Reactions; Evano, G., Blanchard, N., Eds.; Wiley-VCH: Weinheim, 2013. (f) Ruiz-Castillo, P.; Buchwald, S. L. Chem. Rev. 2016, 116, 12564−12649. (g) Niu, H.; Cai, J.; Zhao, P.; Wang, C.; Bai, X.; Wang, W. Dyes Pigm. 2013, 96, 158−169. (3) For oxidative C−C coupling of dialkyl- or monoalkylarylamines, see: (a) Periasamy, M.; Jayakumar, K. N.; Bharathi, P. J. Org. Chem. 2000, 65, 3548−3550. (b) Xi, C.; Jiang, Y.; Yang, X. Tetrahedron Lett. 2005, 46, 3909−3911. (c) Kirchgessner, M.; Sreenath, K.; Gopidas, K. R. J. Org. Chem. 2006, 71, 9849−9852. (d) Ling, X.; Xiong, Y.; Huang, R.; Zhang, X.; Zhang, S.; Chen, C. J. Org. Chem. 2013, 78, 5218−5226. For oxidative C−C coupling of triarylamines, see: (e) Li, X.-L.; Huang, J.-H.; Yang, L.-M. Org. Lett. 2011, 13, 4950−4953. (f) Sreenath, K.; Suneesh, C. V.; Kumar, V. K. R.; Gopidas, K. R. J. Org. Chem. 2008, 73, 3245−3251. (g) Bortoluzzi, M.; Marchetti, F.; Pampaloni, G.; Pinzino, C.; Zacchini, S. Inorg. Chem. 2016, 55, 887−893. (4) Saitoh, T.; Yoshida, S.; Ichikawa, J. J. Org. Chem. 2006, 71, 6414− 6419. (5) (a) Grzybowski, M.; Skonieczny, K.; Butenschön, H.; Gryko, D. T. Angew. Chem., Int. Ed. 2013, 52, 9900−9930. (b) Talipov, M. R.; Hossain, M. M.; Boddeda, A.; Thakur, K.; Rathore, R. Org. Biomol. Chem. 2016, 14, 2961−2968. (c) Talipov, M. R.; Boddeda, A.; Hossain, M. M.; Rathore, R. J. Phys. Org. Chem. 2016, 29, 227−233. (6) Rathore, R.; Kochi, J. K. Acta Chem. Scand. 1998, 52, 114−130. (7) Seo, E. T.; Nelson, R. F.; Fritsch, J. M.; Marcoux, L. S.; Leedy, D. W.; Adams, R. N. J. Am. Chem. Soc. 1966, 88, 3498−3503. (8) (a) Moorthy, J. N.; Venkatakrishnan, P.; Natarajan, P.; Lin, Z.; Chow, T. J. J. Org. Chem. 2010, 75, 2599−2609. (b) Moorthy, J. N.;

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b01377. Elaborate synthetic as well as complete characterization (1H and 13C NMR, IR, and mass spectral) details, 1H and 13 C NMR scans of benzidine/naphthidine derivatives and other novel triarylamine precursors, table for optimization conditions, UV−vis and PL curves of 15, compiled 8971


Article

The Journal of Organic Chemistry Venkatakrishnan, P.; Huang, D.-F.; Chow, T. J. Chem. Commun. 2008, 2146−2148. (9) Rathore, R.; Lindeman, S. V.; Kochi, J. K. J. Am. Chem. Soc. 1997, 119, 9393−9404 and references cited therein. (10) (a) Zhai, L.; Shukla, R.; Rathore, R. Org. Lett. 2009, 11, 3474− 3477. (b) Zhai, L.; Shukla, R.; Wadumethrige, S. H.; Rathore, R. J. Org. Chem. 2010, 75, 4748−4760. (11) (a) Miyamura, H.; Shiramizu, M.; Matsubara, R.; Kobayashi, S. Angew. Chem., Int. Ed. 2008, 47, 8093−8095. (b) Newman, M. S.; Khanna, V. K. Org. Prep. Proced. Int. 1985, 17, 422−423. (12) Zhao, X.; Wang, S.; You, J.; Zhang, Y.; Li, X. J. Mater. Chem. C 2015, 3, 11377−11384. (13) Nelson, R. F.; Adams, R. N. J. Am. Chem. Soc. 1968, 90, 3925− 3930. (14) Weinberg, N. L.; Weinberg, H. R. Chem. Rev. 1968, 68, 449−523. (15) (a) Desmarets, C.; Champagne, B.; Walcarius, A.; Bellouard, C.; Omar-Amrani, R.; Ahajji, A.; Fort, Y.; Schneider, R. J. Org. Chem. 2006, 71, 1351−1361. (b) Matsumoto, V.; Dougomori, K.; Tachikawa, S.; Ishii, T.; Shindo, M. Org. Lett. 2014, 16, 4754−4757. (16) (a) Bridger, R. F. J. Org. Chem. 1970, 35, 1746−1750. (b) Bridger, R. F.; Law, D. A.; Bowman, D. F.; Middleton, B. S.; Ingold, K. U. J. Org. Chem. 1968, 33, 4329−4332. (c) Pan, J.; Li, J.; Huang, R.; Zhang, X.; Shen, H.; Xiong, Y.; Zhu, X. Tetrahedron 2015, 71, 5341−5346. (17) (a) Shirota, Y. J. Mater. Chem. 2000, 10, 1−25. (b) Agarwala, P.; Kabra, D. J. Mater. Chem. A 2017, 5, 1348−1373. (18) (a) Adachi, C.; Nagai, K.; Tamoto, N. Appl. Phys. Lett. 1995, 66, 2679−2681. (b) O’ Brien, D. F.; Burrows, P. E.; Forrest, S. R.; Koene, B. E.; Loy, D. E.; Thompson, M. E. Adv. Mater. 1998, 10, 1108−1112. (19) (a) Creason, C. S.; Wheeler, J.; Nelson, R. F. J. Org. Chem. 1972, 37, 4440. (b) Nelson, R. F.; Feldberg, S. W. J. Phys. Chem. 1969, 73, 2623−2626. (c) Rapta, P.; Zeika, O.; Rohde, D.; Hartmann, H.; Dunsch, L. ChemPhysChem 2006, 7, 863−870. (20) (a) Hasegawa, H. J. Phys. Chem. 1962, 66, 834−836. (b) Hall, W. K. J. Catal. 1962, 1, 53−61. (c) Dollish, F. R.; Hall, W. K. J. Phys. Chem. 1965, 69, 2127−2129. (d) Sumalekshmy, S.; Gopidas, K. R. Chem. Phys. Lett. 2005, 413, 294−299. (21) (a) Nelsen, S. F. Chem. - Eur. J. 2000, 6, 581−588. (b) Low, P. J.; Paterson, M. A. J.; Puschmann, H.; Goeta, A. E.; Howard, J. A. K.; Lambert, C.; Cherryman, J. C.; Tackley, D. R.; Leeming, S.; Brown, B. Chem. - Eur. J. 2004, 10, 83−91 and references cited therein. (22) (a) Huang, F.; Cheng, Y.-J.; Zhang, Y.; Liu, M. S.; Jen, A. K.-Y. J. Mater. Chem. 2008, 18, 4495−4509. (b) Huang, C.-F.; Keshtov, M. L.; Chen, F.-C. ACS Appl. Mater. Interfaces 2016, 8, 27006−27011 and references cited therein. (23) For example, see: (a) Yuan, W. Z.; Lu, P.; Chen, S.; Lam, J. W. Y.; Wang, Z.; Liu, Y.; Kwok, H. S.; Ma, Y.; Tang, B. Z. Adv. Mater. 2010, 22, 2159−2163. (b) Yuan, W. Z.; Gong, Y.; Chen, S.; Shen, X. Y.; Lam, J. W. Y.; Lu, P.; Lu, Y.; Wang, Z.; Hu, R.; Xie, N.; Kwok, H. S.; Zhang, Y.; Sun, J. Z.; Tang, B. Z. Chem. Mater. 2012, 24, 1518−1528. (24) Li, J.; Nakagawa, T.; MacDonald, J.; Zhang, Q.; Nomura, H.; Miyazaki, H.; Adachi, C. Adv. Mater. 2013, 25, 3319−3323. (25) (a) Topchiy, M. A.; Dzhevakov, P. B.; Rubina, M. S.; Morozov, O. S.; Asachenko, A. F.; Nechaev, M. S. Eur. J. Org. Chem. 2016, 2016, 1908−1914. (b) Chen, Z.; Wang, S.; Lian, C.; Liu, Y.; Wang, D.; Chen, C.; Peng, Q.; Li, Y. Chem. - Asian J. 2016, 11, 351−355. (26) Yan, M.-Q.; Yuan, J.; Pi, Y.-X.; Liang, J.-H.; Liu, Y.; Wu, Q.-G.; Luo, X.; Liu, S.-H.; Chen, J.; Zhu, X.-L.; Yu, G.-A. Org. Biomol. Chem. 2016, 14, 451. (27) Ionescu, A.; Lento, R.; Mastropietro, T. F.; Aiello, I.; Termine, R.; Golemme, A.; Ghedini, M.; Bellec, N.; Pini, E.; Rimoldi, I.; Godbert, N. ACS Appl. Mater. Interfaces 2015, 7, 4019−4028. (28) Xu, X.; Yang, X.; Wu, Y.; Zhou, G.; Wu, C.; Wong, W.-Y. Chem. Asian J. 2015, 10, 252−262. (29) Chang, P.-Y.; Wang, P.-H.; Lin, W.-C.; Yang, C.-H. New J. Chem. 2016, 40, 9725. (30) (a) Hancock, J. M.; Gifford, A. P.; Zhu, Y.; Lou, Y.; Jenekhe, S. A. Chem. Mater. 2006, 18, 4924−4932. (b) Chen, Z.; Zhang, K. Y.; Tong, X.; Liu, Y.; Hu, C.; Liu, S.; Yu, Q.; Zhao, Q.; Huang, W. Adv. Funct. Mater. 2016, 26, 4386−4396.

(31) (a) Kuwano, R.; Utsunomiya, M.; Hartwig, J. F. J. Org. Chem. 2002, 67, 6479−6486. (b) Hernandez-Perez, A. C.; Caron, A.; Collins, S. K. Chem. - Eur. J. 2015, 21, 16673−16678. (32) Liu, B.; Zhang, Q.; Ding, H.; Hu, G.; Du, Y.; Wang, C.; Wu, J.; Li, S.; Zhou, H.; Yang, J.; Tian, Y. Dyes Pigm. 2012, 95, 149−160. (33) Li, X.-L.; Wu, W.; Fan, X.-H.; Yang, L.-M. Org. Biomol. Chem. 2014, 12, 1232−1236. (34) Kanazawa, Y.; Yokota, T.; Ogasa, H.; Watanabe, H.; Hanakawa, T.; Soga, S.; Kawatsura, M. Tetrahedron 2015, 71, 1395−1402. (35) Hirai, Y.; Uozumi, Y. Chem. - Asian J. 2010, 5, 1788−1795. (36) Wu, X.; Davis, A. P.; Lambert, P. C.; Steffen, L. K.; Toy, O.; Fry, A. J. Tetrahedron 2009, 65, 2408−2414. (37) Hattori, K.; Yamaguchi, K.; Yamaguchi, J.; Itami, K. Tetrahedron 2012, 68, 7605−7612. (38) Casarini, D.; Lunazzi, L.; Macciantelli, D. J. Org. Chem. 1988, 53, 182−185. (39) Hernandez-Perez, A. C.; Collins, S. K. Angew. Chem., Int. Ed. 2013, 52, 12696−12700. (40) Hong, Y.; Liao, J.-Y.; Cao, D.; Zang, X.; Kuang, D.-B.; Wang, L.; Meier, H.; Su, C.-Y. J. Org. Chem. 2011, 76, 8015−8021. (41) Roiban, G.-D.; Mehler, G.; Reetz, M. T. Eur. J. Org. Chem. 2014, 2014, 2070−2076. (42) (a) Green, R. A.; Hartwig, J. F. Org. Lett. 2014, 16, 4388−4391. (b) Green, R. A.; Hartwig, J. F. Angew. Chem., Int. Ed. 2015, 54, 3768− 3772. (43) Gao, K.; Yorimitsu, H.; Osuka, A. Eur. J. Org. Chem. 2015, 2015, 2678−2682. (44) Natera, J.; Otero, L.; Sereno, L.; Fungo, F.; Wang, N.-S.; Tsai, Y.M.; Hwu, T.-Y.; Wong, K.-T. Macromolecules 2007, 40, 4456−4463. (45) Hariharan, P. S.; Prasad, V. K.; Nandi, S.; Anoop, A.; Moon, D.; Anthony, S. P. Cryst. Growth Des. 2017, 17, 146−155. (46) Tang, X.; Liu, W.; Wu, J.; Lee, C. S.; You, J.; Wang, P. J. Org. Chem. 2010, 75, 7273−7278. (47) Betou, M.; Sallustrau, A.; Toupet, L.; Trolez, Y. Tetrahedron Lett. 2015, 56, 4627−4630. (48) Cai, L.; Qian, X.; Song, W.; Liu, T.; Tao, X.; Li, W.; Xie, X. Tetrahedron 2014, 70, 4754−4759. (49) (a) Gräf, K.; Rahim, M. A.; Das, S.; Thelakkat, M. Dyes Pigm. 2013, 99, 1101−1106. (b) Haberkorn, N.; Weber, S. A. L.; Berger, R.; Theato, P. ACS Appl. Mater. Interfaces 2010, 2, 1573−1580. (50) Tomkeviciene, A.; Simokaitiene, J.; Grazulevicius, J. V.; Jankauskas, V. J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 4674−4680. (51) Cheng, Y.-J.; Liao, M.-H.; Shih, H.-M.; Shih, P.-I.; Hsu, C.-S. Macromolecules 2011, 44, 5968−5976. (52) (a) Okumoto, K.; Shirota, Y. Chem. Mater. 2003, 15, 699−707. (b) Ishihara, M.; Okumoto, K.; Shirota, Y. J. Photopolym. Sci. Technol. 2002, 15, 769−773. (53) Wang, Y.; Lai, G.; Li, Z.; Ma, Y.; Shen, Y.; Wang, C. Tetrahedron 2015, 71, 2761−2767. (54) Low, P. J.; Paterson, M. A. J.; Goeta, A. E.; Yufit, D. S.; Howard, J. A. K.; Cherryman, J. C.; Tackley, D. R.; Brown, B. J. Mater. Chem. 2004, 14, 2516−2523. (55) Koene, B. E.; Loy, D. E.; Thompson, M. E. Chem. Mater. 1998, 10, 2235−2250. (56) (a) Hatakeyama, T.; Imayoshi, R.; Yoshimoto, Y.; Ghorai, S. K.; Jin, M.; Takaya, H.; Norisuye, K.; Sohrin, Y.; Nakamura, M. J. Am. Chem. Soc. 2012, 134, 20262−20265. (b) Jong, H.; Eey, S. T.-C.; Lim, Y. H.; Pandey, S.; Iqbal, N. A. B.; Yong, F. F.; Robins, E. G.; Johannes, C. W. Adv. Synth. Catal. 2017, 359, 616−622. (57) Li, X.-L.; Huang, J.-H.; Yang, L.-M. Org. Lett. 2011, 13, 4950− 4953. (58) Velich, V.; Kozeny, M.; Ticha, E. Collect. Czech. Chem. Commun. 1971, 36, 4107−4110. (59) Hsu, C.-H.; Radu, N. S.; Harmer, M. A. U.S. patent US 7781550 B1, 2010. (60) Kim, T.-S.; Kim, D.-H.; Lee, K.-H.; Lim, C.-W.; Kwak, J.-H.; Son, J.-H.; Chun, M.-S.; Park, Y.-H.; Choi, K.-H.; Kim, M.-K. U. S. Pat. Appl. Publ. US 20110114930 A1, 2011. (61) Oda, K.; Fujita, T. PCT Int. Appl. WO 2014208767 A1, 2014. 8972


Metal-Free Oxidative CâC Coupling of Arylamines ... - ACS Publications

Recommend Documents

Metal-Free Oxidative CâC Coupling of Arylamines ... - ACS Publications