Palladium-Catalyzed Reaction of [60]Fullerene with Aroyl Compounds

Dec 21, 2017 - A convenient and highly efficient palladium-catalyzed reaction of [60]fullerene (C60) with aroyl compounds via enolate-mediated C–H a...
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Article Cite This: J. Org. Chem. 2018, 83, 672−683

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Palladium-Catalyzed Reaction of [60]Fullerene with Aroyl Compounds via Enolate-Mediated sp2 C−H Bond Activation and Hydroxylation Yi-Teng Yan,† Wei Gao,† Bo Jin,*,†,‡ Dong-Shi Shan,† Ru-Fang Peng,*,†,‡ and Shi-Jin Chu† †

State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials, Southwest University of Science and Technology, Mianyang, Sichuan 621010, P. R. China ‡ Department of Chemistry, School of Materials Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, China S Supporting Information *

ABSTRACT: A convenient and highly efficient palladium-catalyzed reaction of [60]fullerene (C60) with aroyl compounds via enolatemediated C−H activation and hydroxylation has been exploited for the first time to synthesize novel C60-fused dihydrofurans, and rare 1,4-fullerenols. Further functionalization including etherification, and esterification of synthesized 1,4-fullerenols provided efficient access to versatile fullerene derivatives. Moreover, a plausible reaction mechanism leading to the observed products is proposed.

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by palladium acetate in trifluoroacetic acid.7d In 2012, both Dong et al. and Rao et al. reported the ketone-directed orthohydroxylation of arylketones in the presence of a palladium catalyst.7e,f More recently, Wang and colleagues reported the reaction of C60 with sec-alkyl aryl ketones in the presence of Pd(OTf)2(MeCN)4 that produced C60-fused tetralones for the first time.3d Inspired by these successes in C−H activation driven by weak coordination, herein we introduced βaryldicarbonyl compounds and isopropyl phenyl ketones, respectively, coupled with [60]fullerene to obtained highproductivity C60-fused dihydrofurans, and monohydroxylated 1,4-fullerenols. Dihydrofuran-fused C60 derivatives have been studied.8 However, the palladium-catalyzed synthesis of C60-fused dihydrofurans remains infrequent and challenging. Compared with previous works, we report the first example of C60-fused dihydrofurans produced from the palladium-catalyzed enolatedirected annulation of C60 with β-aryldicarbonyl compounds. Fullerenols are among the best studied fullerene derivatives with interesting bioactivity properties for potential medicinal applications.9 In addition, they may serve as synthetic precursors through the hydroxyl group for further transformation.10 However, the synthesis of fullerenols with structural diversity is relatively underdeveloped. Relatively few monohydroxylated fullerenols have been investigated, and only

INTRODUCTION Owing to potential properties applicable to materials science, biomedicine, and nanotechnology, the chemical modification of fullerenes or their derivatives has been extensively studied for the last two decades.1 Exploring new methods for chemically modifiying fullerenes is valuable for increasing their utilization efficiency and expanding the range of potential applications. Recently, transition-metal-catalyzed direct transformations have been proven effective and considered synthetically useful for constructing various functional fullerenes.2 Among these metalmediated methods, the palladium-catalyzed C−H activation strategy has remained underdeveloped because of its catalytic efficiency and substrate compatibility.3 Most of its reactions use directing groups to form palladacycles and subsequently produce C60-fused heterocycles or C60-fused carbocycles. During the past decade, C−H bond activation catalyzed by the weak coordination of transition metals,4 especially palladium,5 has been proven a highly selective and atomeconomic method for synthesizing aromatic and heteroaromatic compounds. Ketones are a readily available feedstock, but they are a weakly coordinated directing group (compared with oximes, amides, amines, imines, carboxylic acids, and esters).6 Hence, relatively few reports have investigated ketonedirected/mediated C−H functionalization reactions.7 Most studies on ketone-directed C−H activation used Ru catalysts and only resulted in the C−C coupling products.7a−c In 2010, Cheng and co-workers reported the synthesis of phenanthrone derivatives from sec-alkyl aryl ketones and aryl iodides catalyzed © 2017 American Chemical Society

Received: October 16, 2017 Published: December 21, 2017 672

DOI: 10.1021/acs.joc.7b02620 J. Org. Chem. 2018, 83, 672−683

Article

The Journal of Organic Chemistry Table 1. Optimizing the Reaction Conditions for the Pd-Catalyzed Reaction of C60 with 1aa

entry

oxidant

molar ratiob

solvents

yield (%)c

1 2 3 4 5 6d 7d 8 9 10e 11f 12g 13g 14g 15h 16i

 K2S2O8 Na2S2O3 Ag2O Cu(OAc)2 Cu(OAc)2 Cu(OAc)2 Cu(OAc)2 Cu(OAc)2 Cu(OAc)2 Cu(OAc)2 Cu(OAc)2 Cu(OAc)2 Cu(OAc)2 Cu(OAc)2 Cu(OAc)2

1:3:0.2:0 1:3:0.2:3 1:3:0.2:3 1:3:0.2:3 1:3:0.2:3 1:3:0.2:3 1:3:0.2:3 1:3:0.2:3 1:5:0.2:5 1:5:0.2:5 1:5:0.2:5 1:5:0.2:5 1:5:0.2:5 1:5:0.2:5 1:5:0.2:5 1:5:0.4:5

PhCl PhCl PhCl PhCl PhCl PhCl/PTSA PhCl/TsOH PhCl/TFA (8:1) PhCl/TFA (8:1) PhCl/TFA (8:1) PhCl/TFA (8:1) PhCl/TFA (8:1) PhCl/TFA (8:1) PhCl/TFA (8:1) PhCl/TFA (8:1) PhCl/TFA (8:1)

9 (71) trace trace 11 (53) 14 (68) trace 8 (80) 19 (63) 33 (47) 15 (56) 18 (47) 17 (50) 27 (52) 26 (40) 21 (59) 24 (38)

Unless otherwise indicated, all reactions were performed with 0.05 mmol of C60 in the indicated solvent at 120 °C for 24 h. bMolar ratio refers to molar ratio of C60:1a:catalyst:oxidant. cIsolated yields after column chromatography. Values in parentheses were based on recovered C60. d1.0 equiv of PTSA and TsOH was used, respectively. eThe reaction was performed without Pd(OAc)2. fPdCl2 was adopted as the catalyst. gThe reaction was carried out for 12, 20, 28 h, respectively. hThe reaction was performed in 100 °C. i40 mol % Pd(OAc)2 was used. a

Scheme 1. Results of the Pd-Catalyzed Reaction of C60 with β-Aryldiketones 1a−fa,b

a

Unless otherwise indicated, all reactions were performed with 0.05 mmol of C60, 0.25 mmol of 1, 0.25 mmol of oxidant, 0.01 mmol of Pd(OAc)2 (20 mol %) in chlorobenzene/TFA (8:1, v/v) at 120 °C for 24 h. bIsolated yields after column chromatography. Values in parentheses are based on consumed C60. cReaction was performed at 100 °C for 18 h.

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DOI: 10.1021/acs.joc.7b02620 J. Org. Chem. 2018, 83, 672−683

Article

The Journal of Organic Chemistry Table 2. Optimizing the Reaction Conditions for the Pd-Catalyzed Reaction of C60 with 3aa

entry

oxidant

solvents

yieldb(%)

1 2 3 4 5 6c 7d 8e

Cu(OAc)2 Ag2O K2S2O8 K2S2O8 K2S2O8 K2S2O8 K2S2O8 K2S2O8

PhCl/TFA (8:1) PhCl/TFA (8:1) PhCl/TFA (8:1) PhCl/TFA (8:2) PhCl/TFA (8:3) PhCl/HOTf PhCl PhCl/TFA (8:2)

12 (54) 17 (41) 22 (47) 31 (58) 19 (43) NR NR NR

a Unless otherwise indicated, all reactions were performed with 0.05 mmol of C60, 0.25 mmol of 3a, 0.25 mmol of oxidant, 0.01 mmol of Pd(OAc)2 in the indicated solvent at 120 °C for 10 h. bIsolated yields after column chromatography. Values in parentheses were based on recovered C60. c1.0 equiv of HOTf was added into the solvent. dThe reaction was performed without the TFA. eThe reaction was performed without the catalyst.

the absence of Pd(OAc)2 under other identical conditions (Table 1, entry 10). This result strongly indicated that Pd(OAc)2 served as a catalyst and greatly improved the transformation. It should be noted that the formation mechanism of product 2a is similar to the reported procedure8c when the reaction was performed in the absence of Pd(OAc)2. Notably, a lower yield (18%, 47% based on consumed C60) was obtained when PdCl2 replaced Pd(OAc)2 in the reaction (Table 1, entry 11), which indicated that PdCl2 is inferior compared with Pd(OAc)2 under the current experimental conditions. Nevertheless, modifying the reaction time from 12 h to 20 and 28 h decreased the efficiency (17−27%, 40−52%, respectively, based on consumed C60) (Table 1, entries 12−14). Lowering the reaction temperature from 120 to 100 °C diminished the yields (21% and 59%, respectively, based on consumed C60) (Table 1, entry 15). Increasing the loading of Pd(OAc)2 did not increase the yield (Table 1, entry 16). With the obtained optimum conditions, the substrate scope and limitations were investigated. Various substituent groups, such as methyl, methoxy, or nitro at the para position of the phenyl ring, were all tolerated (Scheme 1). Substrates equipped with electron-donating groups, such as 1b and 1c, achieved products 2b at 21% yield and 2c at 19% yield (56% and 60%, respectively, based on consumed C60). Notably, the substrates bearing strong electron-withdrawing groups (1e) were highly reactive and produced 2e at 39% yield (55% based on consumed C60). This relatively high yield was probably due to the high ratio of the enol form in the substrate bearing an electron-withdrawing group than the substrate with an electrondonating group. The substrate bearing a naphthalene ring (1f) was compatible and gave 2f at 26% yield. Under the employed standard conditions, substrate 1d was less reactive and tended to generate additional byproducts. Thus, reaction temperature and reaction time were decreased and the desired product 2d was obtained at 13% yield (52% based on consumed C60). However, other heterocylic substrates with electron-rich groups such as furan and thiophene were incompatible, probably due to the poor reactivity. Scheme 1 suggests that the sp2 C−H bond activation of alkene is significantly more reactive than that of the aryl ortho

a few such compounds have been obtained by the singleelectron transfer reaction of C60 with (RFCO2)O,11 N−O bond cleavage of [60]fullereno[1,2d]isoxazole in the presence of triethylamine,12 hydrolysis of chlorofullerenes,13 nucleophilic substitution reaction of C60O with aromatic compounds in the presence of BF3·Et2O,14 aminolysis of an unsubstituted [60]fullerene-fused lactone,15 reaction of C60 with water catalyzed with Cp2MCl2,16 reaction of C60 with 4-substituted phenylhydrazine hydrochlorides in the presence of NaNO2,17 or C60 with acid chlorides promoted by Fe(ClO4)3.18 Among the reported monohydroxylated fullerenols (C60ROH), only three were formed in 1,4-addition mode.11,13,17 To the best of our knowledge, Pd-catalyzed monohydroxylated fullerenols have not been investigated. We herein report this novel and rare 1,4-fullerenols produced from the Pd-catalyzed enolatemediated hydroxylation of C60 with isopropyl phenyl ketones.

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RESULTS AND DISCUSSION For the initial reactivity study, readily available ethyl benzoylacetate (1a) was chosen as the model substrate to react with C60 and optimize the reaction conditions. C60 (36 mg, 0.05 mmol), 1a (3 equiv), and Pd(OAc)2 (0.01 mmol, 20 mol %) were stirred in 8 mL of chlorobenzene at 120 °C for 24 h to produce the desired product 2a with 9% yield (71% based on consumed C60) (Table 1, entry 1). To further improve the yield, several other oxidants including K2S2O8, Na2S2O3, Ag2O, and Cu(OAc)2 were explored, and Cu(OAc)2 provided an augmented yield of 14% (Table 1, entry 5 versus entries 2−4). Adding acid generates highly electrophilic cationic Pd(II) species and is proven to be more reactive toward C−H bond activation.3a,c,5e,19 Therefore, the influence of acid additives were examined (Table 1, entries 6−8) and indicated that trifluoroacetic acid (TFA) can provide a better result than those of PTSA and TsOH. Notably, the TFA loss during the reaction may have decelerated the reaction and decreased the product yield. The yield was sensitive to the molar ratio of starting materials and oxidant. Adding 5 equiv of 1a and oxidant substatially raised the yield of 2a to 33% (47% based on consumed C60) (Table 1, entry 9). In addition, a lower yield (15%, 56% based on consumed C60) of 2a was also obtained in 674

DOI: 10.1021/acs.joc.7b02620 J. Org. Chem. 2018, 83, 672−683

Article

The Journal of Organic Chemistry Scheme 2. Results of the Pd-Catalyzed Reaction of C60 with Isopropyl Phenyl Ketones 3a−ga,b

a Unless otherwise indicated, all reactions were performed with 0.05 mmol of C60, 0.25 mmol of 3a−g, 0.25 mmol of oxidant, 0.01 mmol of Pd(OAc)2 (20 mol %) in the listed solvent at 120 °C for 10 h. bIsolated yields after column chromatography. Values in parentheses were based on recovered C60. c40 mol % Pd(OAc)2 at 120 °C for 12 h.

sp2 C−H bond under our conditions, which could undergo the palladium-catalyzed enolate-directed sp2 C−H activation to generate 2. Next, the reactivity of isopropyl phenyl ketone 3a was also examined. Interestingly, an unexpected monohydroxylated 1,4fullerenol 4a instead of the desired product under the above optimal conditions. We began our exploration by using isopropyl phenyl ketone 3a as the representative substrate to react with C60 and optimize the reaction conditions (Table 2). The initial use of 5 equiv of 3a, 5 equiv of Cu(OAc)2 as the oxidant, 1 mL of TFA as additive, and 20 mol % of Pd(OAc)2 as catalyst in 8 mL of chlorobenzene at 120 °C provided 4a at 12% yield (54% based on consumed C60) (Table 2, entry 1). To further improve the yield, other oxidants, including Ag2O, and K2S2O8 were explored; K2S2O8 provided the best yield of 4a at 22% (Table 2, entry 3 versus entries 1 and 2). To our satisfaction, the highest yields (31%, 58% based on consumed C60) were achieved by increasing the volume of TFA to 2 mL. By contrast, increasing the TFA volume to 3 mL did not augment the yield (Table 2, entry 5 versus entry 4). Notably, no desired product 4a was identified when the reaction was performed in the presence of trifluoromethanesulfonic acid (HOTf) and in the absence of TFA (Table 2, entries 6 and 7). This result indicated that TFA played an important role in this reaction. Similarly, no desired product 4a was detected when the reaction was performed in the absence of Pd(OAc)2 (Table 2, entry 8). The substrate scope of this new reaction was investigated by employing other representative isopropyl phenyl ketones 3b−g (Scheme 2). Substrates bearing different substituent groups on

the position of the phenyl ring were tolerated in this transformation. Substrates with electron-withdrawing groups, including Cl and Br, may be efficiently transformed into the desired products 4b and 4c at 33% and 34% yields, respectively, and enable further synthetic transformations. Remarkably, the substrate with a meta-Br on the phenyl ring could also react with C60 with high regioselectivity to provide 4d in 28% yield. However, electron-rich substituents such as methyl, methoxy, ethyoxyl at the para position of the phenyl ring were less reactive than that of unsubstituted 3a, which provided corresponding products 4e−g in 16−28%. Although this protocol afforded the corresponding products in up to 33% yield, the efficiency and selectivity of the present reaction were not high because a notable amount of C60 was transformed to some unidentified less-polar byproducts. Given the unique structure of monohydroxylated fullerenols 4, we performed the control experiments to testify whether we could get fullerene diols C60(OH)2. The reaction was treated with HI in the presence of CS2. However, the desired synthesis was not successful. Product 2a was a known compound; its identity was confirmed by comparison of spectral data with reported in the literatures.8c The structures of C60-fused dihydrofurans 2b− f and monohydroxylated fullerenols 4a−g were fully characterized by MALDI-TOF mass, 1H NMR, 13C NMR, FT-IR, and UV−vis spectra. All the mass spectra of these products gave correct molecular ion peaks. Moreover, all of the 1H NMR results displayed the expected chemical shifts and splitting patterns for all protons. The 13C NMR spectra of 2b−f exhibited no more than 30 675

DOI: 10.1021/acs.joc.7b02620 J. Org. Chem. 2018, 83, 672−683

Article

The Journal of Organic Chemistry Scheme 3. Proposed Reaction Mechanism for the Formation of C60-Fused Dihydrofurans

Scheme 4. Proposed Reaction Mechanism for the Formation of Monohydroxylated Fullerenol 4a

patterns of 4a−g were established by the C1 molecular symmetry deduced from their 13C NMR spectra. On the basis of the above experimental results and previous literature,3,8 we proposed a possible reaction mechanism for the formation of 2a−f that uses 1a as the representative substrate (Scheme 3). Given that 1a is a typical substrate for enol−keto tautomerism, the initial step should involve the palladiumcatalyzed enolate-directed sp2 C−H activation to form the palladacycle A (path a). Then, carbopalladation of C60 by species A generates the six-membered-ring intermediate B. Subsequent reductive elimination of B produces C60-fused dihydrofuran 2a and Pd(0). The Pd(0) is reoxidized to a Pd(II) species by the oxidant to complete the catalytic cycle. In light of the weak coordination of Pd−OR species, adding TFA is believed to enhance the catalytic ability of Pd(II) and

peaks, with two half intensity peaks in the range of 135−149 ppm for the sp2-carbons of the C60 cage. These findings were fully consistent with the CS symmetry of their molecular structures. Two sp3-carbons of the C60 skeleton were located at 72.21−74.61 and 99.73−102.93 ppm, respectively, which were close to those of the previously reported C60-fused dihydrofuran derivatives.8 The 13C NMR spectra of 4a−g clearly displayed at least 46 peaks, including some overlapped peaks, for the 58 sp2-carbons of the C60 cage in the range of 136−154 ppm and two peaks at 75.66−76.21 and 96.95−99.70 ppm, respectively, for the two sp3-carbons of the C60 skeleton. These data were fully consistent with the C1 symmetry of molecular structures in question. Notably, given its low solubility, 4e provided a 13C NMR spectra with poor signal/noise ratios. In the 1,4-addition, 676

DOI: 10.1021/acs.joc.7b02620 J. Org. Chem. 2018, 83, 672−683

Article

The Journal of Organic Chemistry Scheme 5. Further Transformation of 1,4-Fullerenols 4b and 4ca,b

Unless otherwise specified, all reactions were performed at 100 °C, molar ratio of 4a/4b/4c:TsOH = 1:15. bIsolated yield after column chromatography. Values in parentheses were based on recovered fullerenol. cReaction was performed in CS2 at an oil bath temperature of 80 °C, molar ratio of 4b:Ac2O:TsOH = 1:15:10.

a

E,7e,f followed by insertion of C60, generates intermediate F. Subsequent reductive elimination with trifluoroacetic acid (TFA) gives a mixed anhydride species G. The trifluoroacetated product G then converted into final fullerenol product 4a after aqueous workup. Fullerenols may serve as synthetic precursors through the hydroxyl group for further transformation. Esterification was attempted by reacting 4b with anhydride in the presence of ptoluenesulfonic acid (TsOH) to produce 5a at 52% yield. The etherification reaction was efficient and gave products 5b−i at 51−65% yields (Scheme 5). The structures of products 5a−i were also fully characterized by MALDI-TOF mass, 1H NMR, 13C NMR, FT-IR, and UV− vis spectra. It is noteworthy that etherified and acetoxylated fullerenols showed much fewer peaks (no more than 56 peaks)

consequently promote the activation of C−H on double bonds. Alternatively, a possible reaction mechanism in the absence of Pd(OAc)2 under other identical conditions leading to the formation of C60-fused dihydrofurans was assumed to proceed via radical formation (path b).8c,21 Although details about the mechanism remain to be ascertained, on the basis of the above experimental results and previous literature,7e,f,20 a plausible Pd(II)/Pd(IV) catalytic cycle mechanism for the formation of monohydroxylated fullerenols 4a−g are proposed in Scheme 4. The first step likely involves chelation of palladium to the carbonyl oxygen atom in isopropyl phenyl ketone to form C, which, upon deprotonation, would release a molecule of HOAc via enolization to generate an intermediate D.21h Oxidative addition of the Pd(II) complex D to give Pd(IV) complex 677

DOI: 10.1021/acs.joc.7b02620 J. Org. Chem. 2018, 83, 672−683

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The Journal of Organic Chemistry for the sp 2 -carbons of the C 60 cage compared with corresponding fullerenol material (4a, 4b, and 4c); the δc value for the sp3-carbon of the C60 cage was close to each other. Electrochemical properties of 2a−f along with C60 were investigated by cyclic voltammetry (CV), and their half-wave reduction potentials, onset reduction potentials, and LUMO energy levels are summarized in Table 3. The obtained

mmol), TFA (1 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The reaction was stirred at 120 °C for 24 h. After the reaction was completed, the reaction solution was evaporated under vacuum, and the residue was chromatographed on a silica gel column eluting with CS2. The first purple band was unreacted C60; the second brown band was eluted with toluene/hexane (5:2 v/v unless specified) to afford the desired product 2. Compound 2a. By following the general procedure, C60 (36.0 mg, 0.05 mmol) with 1a (48.0 mg, 0.25 mmol), Pd(OAc)2 (2.2 mg, 0.01 mmol), Cu(OAc)2 (50.0 mg, 0.25 mmol), TFA (1 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The reaction was stirred at 120 °C for 24 h, which afforded 2a (15.0 mg, 33%) as a brown amorphous solid along with unreacted C60 (10.7 mg, 30%) after purification by column chromatography. The spectral data were consistent with those previously reported in the literature.8c 1H NMR (400 MHz, CS2/CDCl3) δ 8.09−8.02 (m, 2H), 7.56−7.50 (m, 3H), 4.20 (q, J = 7.1 Hz, 2H), 1.14 (t, J = 7.1 Hz, 3H); 13C NMR (100 MHz, CS2/CDCl3, all 2C unless indicated) δ 165.4 (1C), 162.5 (1C), 147.3, 147.0 (1C), 146.4, 146.3 (1C), 145.7, 145.4, 145.22, 145.16, 145.00, 144.94, 144.6, 144.4, 144.2, 144.0, 143.8, 143.5, 143.4, 143.2, 141.78, 141.76, 141.67, 141.51, 141.45, 141.32, 141.27, 140.6, 140.5, 138.9, 138.4, 136.5 (1C), 134.5, 130.1 (1C, aryl C), 129.1 (aryl C), 128.5 (1C, aryl C), 126.9 (aryl C), 103.7 (1C), 101.1 (sp3-C of C60), 72.2 (sp3-C of C60), 59.6 (1C), 13.1 (1C); FT-IR (KBr) ν/cm−1: 2967, 2930, 2856, 1728, 1632, 1494, 1462, 1384, 1260, 1187, 1081, 962, 802, 742, 691, 520; UV−vis (CHCl3) λ/(nm): 256, 315, 426; HRMS (MALDI-TOF) m/z calcd for C71H10O3 [M+] 910.0624, found 910.0612. Compound 2b. By following the general procedure, C60 (36.0 mg, 0.05 mmol) with 1b (51.5 mg, 0.25 mmol), Pd(OAc)2 (2.2 mg, 0.01 mmol), Cu(OAc)2 (50.0 mg, 0.25 mmol), TFA (1 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The reaction was stirred at 120 °C for 24 h, which afforded 2b (9.7 mg, 21%) as a brown amorphous solid along with unreacted C60 (22.5 mg, 63%) after purification by column chromatography; 1H NMR (600 MHz, CS2/ CDCl3) δ 7.99 (d, J = 8.0 Hz, 2H), 7.36 (d, J = 8.0 Hz, 2H), 4.24 (q, J = 7.1 Hz, 2H), 2.52 (s, 3H), 1.19 (t, J = 7.1 Hz, 3H); 13C NMR (150 MHz, CS2/CDCl3, all 2C unless indicated) δ 166.5 (1C), 163.6 (1C), 148.3, 147.9 (1C), 147.3, 147.2 (1C), 146.3, 146.08, 146.03, 145.88, 145.81, 145.5, 145.3, 145.0, 144.9, 144.7, 144.4 (3C), 144.1, 142.66, 142.63, 142.55, 142.4, 142.3, 142.2, 142.15, 141.5, 141.4 (4C), 139.8, 139.2, 137.4, 135.4, 130.0 (aryl C), 128.5 (aryl C), 126.4 (1C, aryl C), 103.9 (1C), 101.8 (sp3-C of C60), 73.1 (sp3-C of C60), 60.5 (1C), 21.8 (1C), 14.0 (1C); FT-IR (KBr) ν/cm−1: 2974, 2917, 2849, 1697, 1640, 1461, 1369, 1325, 1129, 1092, 1048, 915, 727, 526; UV−vis (CHCl3) λ/(nm): 256, 314, 426; HRMS (MALDI-TOF) m/z calcd for C72H12O3 [M+] 924.0792, found 924.0764. Compound 2c. By following the general procedure, C60 (36.0 mg, 0.05 mmol) with 1c (55.5 mg, 0.25 mmol), Pd(OAc)2 (2.2 mg, 0.01 mmol), Cu(OAc)2 (50.0 mg, 0.25 mmol), TFA (1 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The reaction was stirred at 120 °C for 24 h, which afforded 2c (8.9 mg, 19%) as a brown amorphous solid along with unreacted C60 (24.6 mg, 68%) after purification by column chromatography. 1H NMR (600 MHz, CS2/ CDCl3) δ 8.11−8.08 (m, 2H), 7.06−7.03 (m, 2H), 4.26 (q, J = 7.1 Hz, 2H), 3.93 (s, 3H), 1.20 (t, J = 7.1 Hz, 3H); 13C NMR (150 MHz, CS2/CDCl3, all 2C unless indicated) δ 166.2 (1C), 163.7 (1C), 161.8 (1C, aryl C), 148.5, 147.9 (1C), 147.3, 147.2 (1C), 146.3, 146.08, 146.04, 145.88, 145.81, 145.5, 145.3, 145.0, 144.9, 144.7, 144.5, 144.4, 144.1, 142.66, 142.64, 142.56, 142.4, 142.3, 142.2, 142.16, 141.5, 141.4, 139.8, 139.2, 137.4, 135.3, 131.9 (aryl C), 121.3 (1C), 113.2 (aryl C), 103.1 (1C), 101.6 (sp3-C of C60), 73.2 (sp3-C of C60), 60.5 (1C), 55.1 (1C), 14.1 (1C); FT-IR (KBr) ν/cm−1: 2917, 1698, 1635, 1517, 1491, 1365, 1325, 1179, 1104, 1086, 922, 857, 727, 525; UV−vis (CHCl3) λ/(nm): 256, 316, 427; HRMS (MALDI-TOF) m/z calcd for C72H12O4 [M+] 940.0741, found 940.0716.

Table 3. Half-Wave Potentials of Reduction Processes, Onset Reduction Potentials, and LUMO Energy Levels of PCBM with 2a−fa compd

E1

E2

E3

Eredon

LUMO levelb (eV)

PCBM 2a 2b 2c 2e 2f

−0.92 −0.95 −0.96 −1.04 −0.87 −1.04

−1.43 −1.31 −1.34 −1.54 −1.23 −1.58

−2.01 −1.71 −1.74 −2.01 −1.62 −2.07

−0.80 −0.79 −0..80 −0.81 −0.78 −0.80

−3.91 −3.92 −3.91 −3.90 −3.93 −3.91

a

Experimental conditions: 20 mg of C60 derivatives and 0.1 M TBAPF6 in anhydrous o-dichlorobenzene/acetonitrile (5:1, v/v); reference electrode: Ag/Ag+; working electrode: Pt; auxiliary electrode: Pt wire; scanning rate: 50 mV s−1. bEstimated using the following equation: LUMO = −e(Eredon + 4.71).22

products exhibited essentially similar CV behaviors and showed three well-defined and quasi-reversible redox processes in the negative potential range of 0 to −2.5 V versus Ag/Ag+. The first reduction potentials of the E1 of 2a−c and 2f (−0.95 to −1.04 V) were more negative than that of PCBM (−0.92 V); only 2e (−0.87 V) was more positive than PCBM. Furthermore, the E1 values of 2b and 2c, as well as 2f (one electron-donating group on the para position of the phenyl ring), generally shifted more negatively than did 2a and 2e (one electron-withdrawing group on the phenyl ring). The respective onset reduction potentials of PCBM with 2a−f were −0.80, −0.79, −0.80, −0.81, −0.78, and −0.80 V versus Ag/Ag+. On the basis of the onset reduction potentials, the LUMO energy levels were calculated through the formula LUMO = −e(Eredon + 4.71), where Eredon is the onset reduction potential versus Ag/Ag+. The LUMO energy levels of 2b, 2c, and 2f were −3.91, −3.90, and −3.91 eV, respectively. Compared with the LUMO energy levels of PCBM (−3.91 eV), the three C60-fused dihydrofurans may serve potential applications as acceptors in organic photovoltaic devices.

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CONCLUSIONS In summary, we successfully synthesized C60-fused dihydrofurans, and rare 1,4-fullerenols, via Pd-catalyzed enolate-mediated sp2 C−H activation and hydroxylation to functionalize C60 with both β-aryldicarbonyl compounds and isopropyl phenyl ketones for the first time. Furthermore, we transformed the 1,4-fullerenols through etherification and esterification in the presence of p-toluenesulfonic acid. The current protocol provided facile access to C60-fused dihydrofuran derivatives and 1,4-fullerenol derivatives through a one-pot procedure. A possible mechanism involving a palladium-catalyzed enolatemediated sp2 C−H activation and hydroxylation was proposed.

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EXPERIMENTAL SECTION

General Procedure for the Pd-Catalyzed Reaction of C60 with Substrates 1a−f. C60 (0.05 mmol), β-aryldicarbonyl compound 1 (0.25 mmol), Pd(OAc)2 (0.01 or 0.02 mmol), Cu(OAc)2 (0.25 678

DOI: 10.1021/acs.joc.7b02620 J. Org. Chem. 2018, 83, 672−683

Article

The Journal of Organic Chemistry

solution was stirred vigorously in an oil bath preset at 120 °C for 10 h. After the reaction was completed, the solvent was evaporated in vacuo and the residue was directly separated on a silica gel column with CS2 (unless specified) as the eluent. The first purple band was unreacted C60; then the second light yellow band was some byproduct, followed by the third brown band was collected and evaporated to give the desired 4. Fullerenol 4a. By following the general procedure, C60 (36.0 mg, 0.05 mmol) with 3a (37.0 mg, 0.25 mmol), Pd(OAc)2 (2.2 mg, 0.01 mmol), K2S2O8 (67.2 mg, 0.25 mmol), TFA (2 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The resulting solution was stirred vigorously in an oil bath preset at 120 °C for 10 h, which afforded 4a (12.5 mg, 31%) as a brown amorphous solid along with unreacted C60 (16.8 mg, 47%) after purification by column chromatography; 1H NMR (300 MHz, CS2/CDCl3) δ 8.05 (d, J = 7.5 Hz, 2H), 7.58−7.56 (m, 2H), 7.53−7.50 (m, 1H), 3.49 (s, 1H, OH), 1.99 (s, 3H), 1.68 (s, 3H); 13C NMR (100 MHz, CS2/CDCl3, all 1C unless indicated) δ 154.8, 154.3, 152.6, 149.0, 147.8, 147.1, 146.25, 146.21, 146.18, 146.08, 146.04, 145.98, 145.86, 145.82, 145.79, 145.73, 145.6, 145.56, 145.4, 145.1, 145.0 (2C), 144.96, 144.92, 144.86, 144.79 (2C), 144.71, 144.65, 144.53, 144.45, 144.0, 142.74, 142.73, 142.5, 142.4, 142.38, 142.34, 142.08, 142.05 (2C), 142.01, 141.9, 141.87, 141.82, 141.7, 141.63, 141.55, 141.3, 141.1, 139.7 (2C), 139.6, 139.37, 139.35, 139.3, 138.7, 138.1, 137.8, 136.2, 128.9, 128.2 (2C), 126.9 (2C), 110.5, 97.0 (sp3-C of C60), 76.2 (sp3-C of C60), 28.2, 22.2; FTIR (KBr) ν/cm−1: 3442, 2967, 2924, 2852, 1725, 1639, 1491, 1444, 1383, 1263, 1168, 1101, 768, 730, 697, 526; UV−vis (CHCl3) λ/ (nm): 256, 314, 430; HRMS (MALDI-TOF) m/z calcd for C70H12O2 [M+] 884.0832, found 884.0821. Fullerenol 4b. By following the general procedure, C60 (36.0 mg, 0.05 mmol) with 3b (56.5 mg, 0.25 mmol), Pd(OAc)2 (2.2 mg, 0.01 mmol), K2S2O8 (67.2 mg, 0.25 mmol), TFA (2 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The resulting solution was stirred vigorously in an oil bath preset at 120 °C for 10 h, which afforded 4b (15.9 mg, 33%) as a brown amorphous solid along with unreacted C60 (16.2 mg, 45%) after purification by column chromatography; 1H NMR (300 MHz, CS2/CDCl3) δ 7.96 (d, J = 8.6 Hz, 2H), 7.71 (d, J = 8.7 Hz, 2H), 3.57 (s, 1H, OH), 1.99 (s, 3H), 1.68 (s, 3H); 13C NMR (100 MHz, CS2/CDCl3, all 1C unless indicated) δ 154.6, 154.0, 152.2, 148.7, 147.8, 147.2, 146.3, 146.2, 146.13 (3C), 146.0, 145.95, 145.9, 145.87, 145.83, 145.77, 145.66, 145.61, 145.4, 145.05, 145.03, 145.0, 144.98, 144.96, 144.91, 144.84, 144.82, 144.7, 144.6 (2C), 144.5, 144.0, 142.78, 142.77, 142.6, 142.44, 142.43, 142.4, 142.1, 142.07, 142.04, 141.9, 141.86, 141.79, 141.77, 141.7, 141.6, 141.3, 141.1, 139.6, 139.42, 139.41, 139.35, 138.76, 138.72 (2C), 138.0, 137.7, 136.2, 131.4 (2C), 128.6 (2C), 123.9, 110.1, 97.1 (sp3-C of C60), 76.0 (sp3-C of C60), 28.1, 22.2; FT-IR (KBr) ν/cm−1: 2945, 2918, 2325, 1637, 1466, 1419, 1390, 1168, 1007, 828, 519; UV−vis (CHCl3) λ/(nm): 255, 315, 429; HRMS (MALDI-TOF) m/z calcd for C70H1181BrO2 [M+] 963.9922, found 963.9896. Fullerenol 4c. By following the general procedure, C60 (36.0 mg, 0.05 mmol) with 3c (45.5 mg, 0.25 mmol), Pd(OAc)2 (2.2 mg, 0.01 mmol), K2S2O8 (67.2 mg, 0.25 mmol), TFA (2 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The resulting solution was stirred vigorously in an oil bath preset at 120 °C for 10 h, which afforded 4c (15.6 mg, 34%) as a brown amorphous solid along with unreacted C60 (16.3 mg, 45%) and then the desired product 4c (15.6 mg, 34%) as a brown amorphous solid; 1H NMR (300 MHz, CS2/CDCl3) δ 8.02 (d, J = 8.5 Hz, 2H), 7.56 (d, J = 8.7 Hz, 2H), 3.57 (s, 1H, OH), 1.99 (s, 3H), 1.68 (s, 3H); 13C NMR (100 MHz, CS2/ CDCl3, all 1C unless indicated) δ 154.6, 154.0, 152.2, 148.7, 147.8, 147.1, 146.3, 146.2, 146.1, 146.08, 145.98, 145.91, 145.86, 145.83, 145.79, 145.73, 145.62, 145.57, 145.3, 145.01, 145.0, 144.96, 144.94, 144.92, 144.88, 144.8, 144.78, 144.7, 144.52, 144.51, 144.4, 144.0, 142.74, 142.73, 142.5, 142.4, 142.39, 142.36, 142.06, 142.03, 142.0, 141.88, 141.82, 141.75, 141.73, 141.6, 141.5, 141.2, 141.1, 139.6, 139.39, 139.37, 139.31, 138.73, 138.71, 138.2, 138.0, 137.7, 136.6,

Compound 2d. By following the general procedure, C60 (36.5 mg, 0.05 mmol) with 1d (56.1 mg, 0.25 mmol), Pd(OAc)2 (2.2 mg, 0.01 mmol), Cu(OAc)2 (50.0 mg, 0.25 mmol), TFA (1 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The reaction was stirred at 100 °C for 18 h. After the reaction was completed, the solvent was evaporated in vacuo and the residue was directly separated on a silica gel column with CS2 as the eluent to give unreacted C60 (27.4 mg, 75%); subsequent elution with CS2/toluene (10:1 v/v) afforded desired product 2d (6.2 mg, 13%) as a brown amorphous solid; 1H NMR (600 MHz, CS2/CDCl3) δ 7.85 (dd, J = 8.2, 1.4 Hz, 2H), 7.70−7.67 (m, 2H), 7.36−7.32 (m, 2H), 7.26 (t, J = 7.6 Hz, 2H), 7.22−7.20 (m, 2H); 13C NMR (150 MHz, CS2/CDCl3, all 2C unless indicated) δ 191.6 (1C), 163.6 (1C), 148.7, 147.9 (1C), 147.1 (1C), 146.8, 146.3, 146.2, 146.0, 145.89, 145.84, 145.5, 145.3, 145.0, 144.9, 144.8, 144.4, 144.0 (3C), 142.7, 142.6, 142.5, 142.4, 142.3, 142.2, 142.1, 141.6, 141.5, 139.83, 139.78, 138.0 (1C), 137.6, 135.1, 132.2 (1C), 130.8 (1C), 129.5 (4C, aryl C), 128.8 (1C, aryl C), 128.06 (aryl C), 128.02 (aryl C), 111.6 (1C, aryl C), 102.1 (1C), 99.7 (sp3-C of C60), 74.6 (sp3-C of C60); FT-IR (KBr) ν/cm−1: 2918, 1849, 1622, 1445, 1335, 1148, 1006, 889, 691, 525; UV−vis (CHCl3) λ/(nm): 256, 316, 427; HRMS (MALDI-TOF) m/z calcd for C75H10O2 [M+] 942.0686, found 942.0666. Compound 2e. By following the general procedure, C60 (35.9 mg, 0.05 mmol) with 1e (59.3 mg, 0.25 mmol), Pd(OAc)2 (2.2 mg, 0.01 mmol), Cu(OAc)2 (50.0 mg, 0.25 mmol), TFA (1 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The reaction was stirred at 120 °C for 24 h, which afforded 2e (18.6 mg, 39%) as a brown amorphous solid along with unreacted C60 (10.5 mg, 29%) after purification by column chromatography. 1H NMR (600 MHz, CS2/ CDCl3) δ 8.49 (d, J = 8.6 Hz, 2H), 8.37 (d, J = 8.6 Hz, 2H), 4.33 (q, J = 7.1 Hz, 2H), 1.23 (t, J = 7.1 Hz, 3H); 13C NMR (150 MHz, CS2/ CDCl3, all 2C unless indicated) δ 164.0 (1C), 163.2 (1C), 149.1, 148.1, 147.6 (1C), 147.4, 147.2 (1C), 146.5, 146.4, 146.3, 146.1, 146.05, 145.6, 145.55, 145.3, 145.1, 144.6, 144.5, 144.3, 143.8, 142.9 (3C), 142.8, 142.49, 142.46, 142.4, 142.3, 141.6, 141.4, 140.0, 139.5, 137.6, 135.62, 135.56 (1C, aryl C), 131.2 (aryl C), 123.1 (aryl C), 107.1 (1C), 102.8 (sp3-C of C60), 73.0 (sp3-C of C60), 61.2 (1C), 14.1 (1C); FT-IR (KBr) ν/cm−1: 2952, 2917, 2850, 1698, 1635, 1517, 1491, 1179, 922, 857, 727, 525; UV−vis (CHCl3) λ/(nm): 255, 317, 429; HRMS (MALDI-TOF) m/z calcd for C71H9NO5 [M+] 955.0486, found 955.0473. Compound 2f. By following the general procedure, C60 (36.0 mg, 0.05 mmol) with 1f (60.5 mg, 0.25 mmol), Pd(OAc)2 (2.2 mg, 0.01 mmol), Cu(OAc)2 (50.0 mg, 0.25 mmol), TFA (1 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The reaction was stirred at 120 °C for 24 h, which afforded 2f (12.5 mg, 26%) as a brown amorphous solid along with unreacted C60 (17.2 mg, 48%) after purification by column chromatography. 1H NMR (600 MHz, CS2/ CDCl3) δ 8.45 (d, J = 8.4 Hz, 1H), 8.09−8.04 (m, 2H), 7.98 (d, J = 8.2 Hz, 1H), 7.71−7.67 (m, 2H), 7.63−7.59 (m, 1H), 3.96 (q, J = 7.1 Hz, 2H), 0.70 (t, J = 7.1 Hz, 3H); 13C NMR (150 MHz, CS2/CDCl3, all 2C unless indicated) δ 166.2 (1C), 163.5 (1C), 148.2, 148.0 (1C), 147.31, 147.27 (1C), 146.4, 146.3, 146.1, 145.99, 145.93, 145.6, 145.5, 145.1, 145.0, 144.8, 144.5, 144.19, 144.17, 142.76, 142.72, 142.6, 142.5, 142.4, 142.29, 142.23, 141.6, 141.5, 139.9, 139.6, 137.5, 135.4, 133.3 (1C), 131.1 (1C), 130.8 (1C), 128.5 (1C), 128.1 (1C), 127.6 (1C), 127.1 (1C), 126.4 (1C), 125.1 (1C), 124.8 (1C), 108.1 (1C), 102.9 (sp3-C of C60), 72.5 (sp3-C of C60), 60.3 (1C), 13.4 (1C); FT-IR (KBr) ν/cm−1: 2974, 2917, 2849, 1667, 1640, 1461, 1369, 1325, 1129, 1092, 1048, 915, 880, 721, 526; UV−vis (CHCl3) λ/(nm): 256, 315, 426; HRMS (MALDI-TOF) m/z calcd for C75H12O3 [M+] 960.0792, found 960.0769. General Procedure for the Pd-Catalyzed Reaction of C60 with Substrates 3a−g. C60 (0.05 mmol), 3a−g (0.25 mmol), Pd(OAc)2 (0.01 or 0.02 mmol), K2S2O8 (0.25 mmol), TFA (2 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The resulting 679

DOI: 10.1021/acs.joc.7b02620 J. Org. Chem. 2018, 83, 672−683

Article

The Journal of Organic Chemistry 136.2, 135.4, 128.39 (2C), 128.32 (2C), 110.0, 97.0 (sp3-C of C60), 76.0 (sp3-C of C60), 28.1, 22.1; FT-IR (KBr) ν/cm−1: 2925, 2842, 2326, 1629, 1468, 1430, 1167, 1094, 1009, 979, 826, 599, 524; UV−vis (CHCl3) λ/(nm): 256, 315, 429; HRMS (MALDI-TOF) m/z calcd for C70H1135ClO2 [M+] 918.0442, found 918.0426. Fullerenol 4d. By following the general procedure, C60 (36.0 mg, 0.05 mmol) with 3d (56.5 mg, 0.25 mmol), Pd(OAc)2 (2.2 mg, 0.02 mmol), K2S 2O8 (67.2 mg, 0.25 mmol), TFA (2 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The resulting solution was stirred vigorously in an oil bath preset at 120 °C for 10 h, which afforded 4d (13.5 mg, 28%) as a brown amorphous solid along with unreacted C60 (16.8 mg, 47%) after purification by column chromatography; 1H NMR (600 MHz, CS2/CDCl3) δ 8.22 (s, 1H), 7.99 (d, J = 7.4 Hz, 1H), 7.65 (m, 1H), 7.46 (t, J = 7.8 Hz, 1H), 3.51 (s, 1H, OH), 1.99 (s, 3H), 1.69 (s, 3H); 13C NMR (150 MHz, CS2/ CDCl3, all 1C unless indicated) δ 154.8, 154.2, 152.3, 148.8, 148.0, 147.3, 146.44, 146.37, 146.28, 146.26, 146.2, 146.09, 146.02, 146.0, 145.96, 145.91, 145.78, 145.74, 145.5, 145.17, 145.15 (2C), 145.13, 145.1, 145.0, 144.98, 144.95, 144.8, 144.7 (2C), 144.6, 144.2, 142.91, 142.88, 142.7, 142.56, 142.54, 142.52, 142.24, 142.21 (2C), 142.16, 142.1, 142.0 (2C), 141.94, 141.91, 141.78, 141.72, 141.4, 141.3, 139.7, 139.54, 139.51, 139.48, 139.0, 138.1, 137.7, 136.3, 132.2, 130.3, 129.9, 125.7, 122.8, 110.0, 97.3 (sp3-C of C60), 76.2 (sp3-C of C60), 28.3, 22.3; FT-IR (KBr) ν/cm−1: 2917, 2850, 1631, 1463, 1384, 1263, 1094, 1047, 889, 786, 698, 525; UV−vis (CHCl3) λ/(nm): 257, 314, 428; HRMS (MALDI-TOF) m/z calcd for C70H1179BrO2 [M−] 961.9948, found 961.9938. Fullerenol 4e. By following the general procedure, C60 (36.0 mg, 0.05 mmol) with 3e (40.5 mg, 0.25 mmol), Pd(OAc)2 (4.5 mg, 0.02 mmol), K2S 2O8 (67.2 mg, 0.25 mmol), TFA (2 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The resulting solution was stirred vigorously in an oil bath preset at 120 °C for 12 h, which afforded 4e (8.5 mg, 19%) as a brown amorphous solid along with unreacted C60 (17.0 mg, 47%) after purification by column chromatography; 1H NMR (400 MHz, CS2/CDCl3) δ 7.90 (d, J = 8.1 Hz, 2H), 7.34 (d, J = 7.9 Hz, 2H), 3.35 (s, 1H, OH), 2.49 (s, 3H), 1.96 (s, 3H), 1.65 (s, 3H); (It should be noted that the very low solubility of 4e prevented us f rom obtaining a 13C NMR spectrum with a good signal-tonoise ratio); FT-IR (KBr) ν/cm−1: 2918, 2844, 1634, 1464, 1430, 1381, 1169, 1015, 821, 528; UV−vis (CHCl3) λ/(nm): 256, 315, 429; HRMS (MALDI-TOF) m/z calcd for C71H14O2 [M+] 898.0988, found 898.0973. Fullerenol 4f. By following the general procedure, C60 (36.0 mg, 0.05 mmol) with 3f (44.5 mg, 0.25 mmol), Pd(OAc)2 (4.5 mg, 0.02 mmol), K2S 2O8 (67.2 mg, 0.25 mmol), TFA (2 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The resulting solution was stirred vigorously in an oil bath preset at 120 °C for 12 h. After the reaction was completed, the solvent was evaporated in vacuo and the residue was directly separated on a silica gel column with CS2 as the eluent to give unreacted C60 (20.8 mg, 58%); subsequent elution with CS2/toluene (10:1 v/v) afforded desired product 4f (7.2 mg, 16%) as a brown amorphous solid; 1H NMR (400 MHz, CS2/ CDCl3) δ 7.96 (d, J = 8.1 Hz, 2H), 7.06 (d, J = 8.5 Hz, 2H), 3.91 (s, 3H), 3.42 (s, 1H, OH), 1.97 (s, 3H), 1.68 (s, 3H); 13C NMR (150 MHz, CS2/CDCl3, all 1C unless indicated) δ 167.6 (aryl C), 154.5, 153.4, 150.7, 148.16, 148.14, 147.6, 146.8, 146.6, 146.5, 146.4, 146.29 (3C), 146.26, 146.19, 146.17, 146.0, 145.49, 145.47, 145.43, 145.3, 145.2 (3C), 145.1, 145.0 (3C), 144.8, 144.6, 144.4, 143.13, 143.1, 143.0, 142.83 (3C), 142.78, 142.5, 142.37, 142.32 (3C), 142.29 (3C), 142.2, 142.0, 141.95, 141.93, 141.6, 141.0, 139.97, 139.96, 139.93, 139.7, 139.2, 137.0, 136.9, 136.5, 136.3, 131.8, 123.6, 112.6, 98.4 (sp3C of C60), 75.7 (sp3-C of C60), 57.6, 27.7, 22.2; FT-IR (KBr) ν/cm−1: 2953, 2917, 2849, 1622, 1603, 1462, 1384, 1261, 1120, 1048, 799, 526; UV−vis (CHCl3) λ/(nm): 257, 313, 429; HRMS (MALDI-TOF) m/z calcd for C71H14O3 [M+] 914.0937, found 914.0921. Fullerenol 4g. By following the general procedure, C60 (36.0 mg, 0.05 mmol) with 3g (48.0 mg, 0.25 mmol), Pd(OAc)2 (4.5 mg, 0.02

mmol), K2S2O8 (67.2 mg, 0.25 mmol), TFA (2 mL), and chlorobenzene (8 mL) were added to a 48 mL pressure-affordable thick-walled glass tube with a magnetic stirring bar. The resulting solution was stirred vigorously in an oil bath preset at 120 °C for 12 h. After the reaction was completed, the solvent was evaporated in vacuo and the residue was directly separated on a silica gel column with CS2 as the eluent to give unreacted C60 (19.8 mg, 55%); subsequent elution with CS2/CH2Cl2 (10:1 v/v) afforded desired product 4g (8.6 mg, 19%) as a brown amorphous solid; 1H NMR (400 MHz, CS2/ CDCl3) δ 7.93 (d, J = 8.7 Hz, 2H), 7.03 (d, J = 8.9 Hz, 2H), 4.13 (q, J = 6.9 Hz, 2H), 3.39 (s, 1H, OH), 1.96 (s, 3H), 1.67 (s, 3H), 1.50 (t, J = 7.0 Hz, 3H); 13C NMR (150 MHz, CS2/CDCl3, all 1C unless indicated) δ 159.4 (aryl C), 155.0, 154.5, 152.7, 149.2, 147.8, 147.2, 146.28 (2C), 146.22, 146.1, 146.0, 145.89, 145.86, 145.83, 145.76, 145.62, 145.6, 145.5, 145.17, 145.06, 145.01, 145.00, 144.96, 144.87, 144.83 (2C), 144.75, 144.72, 144.58, 144.5, 144.0, 142.78, 142.77, 142.6, 142.43, 142.41, 142.37, 142.1, 142.09 (2C), 142.04, 141.93, 141.92, 141.9, 141.8, 141.67, 141.61, 141.4, 141.1, 139.6, 139.39, 139.37, 139.32, 138.8, 138.1, 137.8, 136.2, 135.7, 131.6, 128.1 (2C), 113.9 (2C), 110.7, 99.7 (sp3-C of C60), 76.2 (sp3-C of C60), 63.3, 31.8, 23.0, 14.4; FT-IR (KBr) ν/cm−1: 2919, 2851, 1631, 1609, 1508, 1462, 1385, 1245, 1167, 1115, 1030, 833, 526; UV−vis (CHCl3) λ/(nm): 256, 314, 429; HRMS (MALDI-TOF) m/z calcd for C72H16O3 [M+] 928.1094, found 928.1085. Control Experiment for the Synthesis of Fullerene Diols C60(OH)2. A mixture of fullerenol 4a (10.0 mg, 0.01 mmol) and HI (20 uL, 0.55 mol/L) was dissolved in CS2 (15 mL), The resulting solution was ultrasonically stirred at room temperature for 27 h. After evaporation in vacuo, the residue was separated on a silica gel column with carbon disulfide as the eluent to give decomposed C60 (5.5 mg, 74%), along with undecomposed 4a (2.2 mg, 22%). Experimental Procedure for Compounds 5a−f. Compound 5a. A mixture of fullerenol 4b (10.0 mg, 0.01 mmol), acetic anhydride (15 uL, 15 equiv), and p-toluenesulfonic acid (20.0 mg, 10 equiv) was dissolved in CS2 (15 mL) and heated with stirring in an oil bath preset at 80 °C. The reaction was monitored by TLC and stopped at the desired time. After evaporation in vacuo, the residue was separated on a silica gel column with carbon disulfide as the eluent to give unreacted fullerenol (3.2 mg, 32%), then with toluene/ethyl acetate (10:1) as the eluent to afford desired product 5a (5.5 mg, 52%); 1H NMR (600 MHz, CS2/CDCl3) δ 8.16−7.88 (m, 1H), 7.70−7.60 (m, 2H), 7.47 (s, 1H), 2.25 (s, 3H), 2.01 (s, 3H), 1.61 (s, 3H); 13C NMR (125 MHz, CS2/CDCl3, all 1C unless indicated) δ 168.3, 154.4, 153.4, 150.6, 148.1, 148.0, 147.5, 146.7, 146.6, 146.4, 146.3, 146.23 (2C), 146.21 (4C), 146.18, 146.11, 146.08, 145.9, 145.4, 145.37, 145.35, 145.2, 145.16 (2C), 145.11, 145.0, 144.95, 144.92, 144.9, 144.8, 144.5, 144.3, 143.03, 142.98, 142.9, 142.73 (2C), 142.69, 142.4, 142.29, 142.24, 142.21, 142.2, 142.17, 142.1, 141.9, 141.88, 141.84, 141.5, 140.9, 139.85, 139.84, 139.8, 139.6, 139.2, 137.8, 136.85, 136.83, 136.4, 136.2, 131.8 (2C), 123.3, 112.8, 98.5 (sp3-C of C60), 75.6 (sp3-C of C60), 27.6, 22.3, 22.1; FT-IR (KBr) ν/cm−1: 2970, 2918, 1754, 1637, 1462, 1430, 1389, 1269, 1196, 1075, 1009, 821, 527; UV−vis (CHCl3) λ/(nm): 256, 314, 429; HRMS (MALDI-TOF) m/z calcd for C72H13O379Br [M+] 1004.0043, found 1004.0040. Etherification of Fullerenols 4b and 4c in the Presence of pToluenesulfonic Acid. To a 25 mL round-bottom flask equipped with a reflux condenser were added fullerenol 4a (4b, 4c, 10.0 mg), ptoluenesulfonic acid (15 equiv), and a mixture of 1,4-dioxane-CS2MeOH/EtOH/BnOH/2-propyn-1-ol/3-butyn-1-ol (16 mL:8 mL:8 mL). The resulting solution was ultrasonically treated and stirred in an oil bath preset at 100 °C. The reaction was monitored by TLC and stopped at the desired time. After the solvent was evaporated in vacuo, the residue was directly separated on a silica gel column with CS2 as the eluent to afford compounds 5b−i, then gave unreacted fullerenols 4a (4b, 4c). Compound 5b. According to the general procedure, the reaction of 4a (10.0 mg, 0.01 mmol), p-toluene sulfonic acid (32.3 mg, 15 equiv), and a mixture of 1,4-dioxane-CS2-2-propyn-1-ol (16 mL:8 mL:8 mL) at 100 °C for 36 h afforded 5b (6.0 mg, 58%) as a brown amorphous solid along with unreacted fullerenol 4a (1.8 mg, 18%) after 680

DOI: 10.1021/acs.joc.7b02620 J. Org. Chem. 2018, 83, 672−683

Article

The Journal of Organic Chemistry purification by column chromatography; 1H NMR (600 MHz, CS2/ CDCl3) δ 8.13 (d, J = 7.7 Hz, 1H), 7.83 (d, J = 7.5 Hz, 1H), 7.59 (q, J = 7.3 Hz, 2H), 7.53 (m, 1H), 4.66 (dd, J = 15.1, 2.5 Hz, 1H), 4.18 (dd, J = 15.1, 2.5 Hz, 1H), 2.38 (t, J = 2.4 Hz, 1H), 2.03 (s, 3H), 1.61 (s, 3H); 13C NMR (150 MHz, CS2/CDCl3, all 1C unless indicated) δ 154.9, 154.1, 150.2, 149.1, 148.0, 147.3, 146.45, 146.43, 146.4, 146.3, 146.18, 146.13, 146.03, 146.01, 145.95, 145.9, 145.88, 145.8, 145.7, 145.2, 145.18, 145.17, 145.15, 145.13, 144.97 (2C), 144.95, 144.86, 144.84, 144.71, 144.65, 144.1, 142.91, 142.88, 142.7, 142.58, 142.55, 142.5, 142.29, 142.27, 142.22, 142.18, 142.16, 142.1, 141.9 (2C), 141.87, 141.8, 141.2 (2C), 139.7, 139.6, 139.4 (2C), 139.1, 138.6, 138.2, 136.3, 135.5, 129.1, 128.8, 128.6 (2C), 126.4, 113.4, 97.4 (sp3-C of C60), 79.8, 76.2 (sp3-C of C60), 73.9, 52.4, 28.3, 22.2; FT-IR (KBr) ν/cm−1: 2919, 2852, 1632, 1400, 1261, 1078, 1013, 615, 523; UV−vis (CHCl3) λ/(nm): 257, 314, 428; HRMS (MALDI-TOF) m/z calcd for C73H12O2 [M−] 922.0999, found 922.0988. Compound 5c. According to the general procedure, the reaction of 4a (10.0 mg, 0.01 mmol), p-toluenesulfonic acid (32.3 mg, 15 equiv), and a mixture of 1,4-dioxane-CS2-3-butyn-1-ol (16 mL:8 mL:8 mL) at 100 °C for 40 h afforded 5c (5.4 mg, 51%) as a brown amorphous solid along with unreacted fullerenol 4a (2.0 mg, 20%) after purification by column chromatography; 1H NMR (600 MHz, CS2/ CDCl3) δ 8.13 (d, J = 8.0 Hz, 1H), 7.81−7.77 (m, 1H), 7.56 (m, 2H), 7.51−7.48 (m, 1H), 4.12 (m 1H), 3.62 (m, 1H), 2.68−2.56 (m, 2H), 2.00 (s, 3H), 1.94 (t, J = 2.6 Hz, 1H), 1.57 (s, 3H); 13C NMR (150 MHz, CS2/CDCl3, all 1C unless indicated) δ 155.4, 154.4, 151.3, 149.5, 148.1, 147.5, 146.61, 146.57, 146.51, 146.4, 146.31, 146.28, 146.17, 146.15, 146.09, 146.06, 146.04, 145.9, 145.6, 145.33 (2C), 145.31 (2C), 145.25, 145.12, 145.1 (2C), 145.0, 144.9, 144.8, 144.3, 143.1, 143.08, 142.9, 142.73, 142.7, 142.68, 142.4, 142.39, 142.37, 142.25 (2C), 142.21, 142.12, 142.11, 142.0 (2C), 141.4, 141.3, 139.9, 139.76, 139.72, 139.6, 139.06 (2C), 137.8 (2C), 136.5, 136.3, 129.01, 128.99, 128.67, 128.64, 126.3, 113.6, 97.5 (sp3-C of C60), 81.5, 76.5 (sp3-C of C60), 69.9, 61.9, 28.6, 22.4, 19.6; FT-IR (KBr) ν/cm−1: 2961, 2923, 2852, 1631, 1462, 1261, 1093, 1021, 803, 702, 525; UV−vis (CHCl3) λ/(nm): 256, 314, 427; HRMS (MALDI-TOF) m/z calcd for C74H16O2 [M−] 936.1156, found 936.1147. Compound 5d. According to the general procedure, the reaction of 4b (10.0 mg, 0.01 mmol), p-toluenesulfonic acid (30.0 mg, 15 equiv), and a mixture of 1,4-dioxane-CS2-2-propyn-1-ol (16 mL:8 mL:8 mL) at 100 °C for 36 h afforded 5d (5.6 mg, 54%) as a brown amorphous solid along with unreacted fullerenol 4b (2.5 mg, 25%) after purification by column chromatography; 1H NMR (600 MHz, CS2/ CDCl3) δ 8.09−8.06 (m, 1H), 7.78 (d, J = 1.4 Hz, 2H), 7.77 (d, J = 1.4 Hz, 1H), 4.71 (dd, J = 15.2, 2.5 Hz, 1H), 4.22 (dd, J = 15.2, 2.4 Hz, 1H), 2.45 (t, J = 2.4 Hz, 1H), 2.06 (s, 3H), 1.65 (s, 3H); 13C NMR (150 MHz, CS2/CDCl3, all 1C unless indicated) δ 153.6, 152.8, 148.9, 147.8, 147.0, 146.3, 145.5, 145.4, 145.32, 145.31, 145.2, 145.05 (2C), 145.04, 144.98, 144.93, 144.92, 144.8, 144.6, 144.2, 144.19, 144.15 (2C), 144.1, 144.01, 143.99 (2C), 143.8, 143.72, 143.7, 143.6, 143.1, 141.93, 141.91, 141.7, 141.62, 141.6, 141.5, 141.3, 141.28, 141.23, 141.2, 141.12, 141.1, 140.9, 140.89, 140.86, 140.8, 140.3, 140.2, 138.8, 138.6, 138.5 (3C), 138.1, 137.5, 137.1, 135.2, 133.7, 130.9 (2C), 129.6, 127.2, 123.0, 112.0, 96.4 (sp3-C of C60), 78.6, 75.0 (sp3-C of C60), 73.3, 51.6, 27.2, 21.1; FT-IR (KBr) ν/cm−1: 2919, 2844, 1631, 1385, 1261, 1167, 1120, 1035, 752, 590, 528; UV−vis (CHCl3) λ/(nm): 256, 315, 428; HRMS (MALDI-TOF) m/z calcd for C73H1379BrO2 [M−] 1000.0104, found 1000.0093. Compound 5e. According to the general procedure, the reaction of 4b (10.0 mg, 0.01 mmol), p-toluenesulfonic acid (30.0 mg, 15 equiv), and a mixture of 1,4-dioxane-CS2-MeOH (16 mL:8 mL:8 mL) at 100 °C for 24 h afforded 5e (6.5 mg, 64%) as a brown amorphous solid along with unreacted fullerenol 4b (1.5 mg, 15%) after purification by column chromatography; 1H NMR (600 MHz, CS2/CDCl3) δ 8.01− 7.99 (m, 1H), 7.69−7.66 (m, 2H), 7.59−7.57 (m, 1H), 3.48 (s, 3H), 1.93 (s, 3H), 1.58 (s, 3H); 13C NMR (150 MHz, CS2/CDCl3, all 1C unless indicated) δ 155.1, 154.2, 151.4, 149.3, 148.1, 147.5, 146.58, 146.52, 146.5, 146.4, 146.3, 146.27, 146.18, 146.14, 146.1, 146.06, 145.95, 145.91, 145.6, 145.3 (2C), 145.29 (2C), 145.26, 145.13, 145.11, 145.1, 145.05, 145.0, 144.9, 144.8, 144.3, 143.09, 143.08,

142.9, 142.75, 142.72, 142.67, 142.4, 142.38, 142.36, 142.23, 142.21 (2C), 142.08, 142.07, 141.9 (2C), 141.5, 141.4, 139.9, 139.7 (2C), 139.6, 139.1, 137.9, 137.7, 136.4, 135.7 (2C), 131.89, 131.82, 130.9, 128.1, 123.6, 113.4, 97.4 (sp3-C of C60), 76.4 (sp3-C of C60), 52.0, 28.4, 22.4; FT-IR (KBr) ν/cm−1: 2924, 2853, 1631, 1485, 1455, 1385, 1263, 1168, 1093, 1006, 824, 754, 526; UV−vis (CHCl3) λ/(nm): 256, 315, 429; HRMS (MALDI-TOF) m/z calcd for C71H1381BrO2 [M+] 978.0093, found 978.0061. Compound 5f. According to the general procedure, the reaction of 4b (10.0 mg, 0.01 mmol), p-toluenesulfonic acid (30.0 mg, 15 equiv), and a mixture of 1,4-dioxane-CS2-EtOH (16 mL:8 mL:8 mL) at 100 °C for 36 h afforded 5f (5.8 mg, 56%) as a brown amorphous solid along with unreacted fullerenol 4b (2.1 mg, 21%) after purification by column chromatography; 1H NMR (600 MHz, CS2/CDCl3) δ 8.01− 7.99 (m, 1H), 7.67−7.65 (m, 2H), 7.59−7.58 (m, 1H), 4.04 (dq, J = 9.6, 7.0 Hz, 1H), 3.47 (dq, J = 9.6, 7.0 Hz, 1H), 1.93 (s, 3H), 1.54 (s, 3H), 1.31 (t, J = 7.0 Hz, 3H); 13C NMR (150 MHz, CS2/CDCl3, all 1C unless indicated) δ 155.4, 154.3, 151.3, 149.4, 148.1, 147.5, 146.58, 146.56, 146.51, 146.4, 146.3, 146.28, 146.17, 146.14, 146.08, 146.05, 145.99, 145.9, 145.7, 145.32, 145.3 (2C), 145.27, 145.23, 145.1, 145.09, 145.08 (2C), 145.0, 144.9, 144.8, 144.3, 143.08, 143.06, 142.9, 142.74, 142.7, 142.66, 142.41, 142.37, 142.36, 142.24, 142.22, 142.2, 142.1 (2C), 141.9 (2C), 141.4, 141.2, 139.9, 139.7, 139.63, 139.57, 139.0, 137.85, 137.83, 136.3, 136.2 (2C), 131.77, 131.72, 130.8, 127.9, 123.3, 113.0, 97.4 (sp3-C of C60), 76.5 (sp3-C of C60), 59.3, 28.5, 22.4, 14.5; FT-IR (KBr) ν/cm−1: 2969, 2916, 1631, 1586, 1425, 1384, 1263, 1166, 1079, 1007, 945, 822, 525; UV−vis (CHCl3) λ/(nm): 257, 314, 430; HRMS (MALDI-TOF) m/z calcd for C72H1581BrO2 [M+] 992.0235, found 992.0244. Compound 5g. According to the general procedure, the reaction of 4b (10.0 mg, 0.01 mmol), p-toluenesulfonic acid (30.0 mg, 15 equiv), and a mixture of 1,4-dioxane-CS2−BnOH (16 mL:8 mL:8 mL) at 100 °C for 30 h afforded 5g (5.5 mg, 52%) as a brown amorphous solid along with unreacted fullerenol 4b (1.8 mg, 18%) after purification by column chromatography; 1H NMR (600 MHz, CS2/CDCl3) δ 8.13− 8.09 (m, 1H), 7.77−7.73 (m, 1H), 7.68−7.67 (m, 2H), 7.40−7.36 (m, 2H), 7.28 (m, 2H), 7.23−7.20 (m, 1H), 5.10 (d, J = 12.4 Hz, 1H), 4.60 (d, J = 12.4 Hz, 1H), 2.06 (s, 3H), 1.64 (s, 3H); 13C NMR (150 MHz, CS2/CDCl3, all 1C unless indicated) δ 154.6, 154.0, 150.2, 149.1, 147.9, 147.3, 146.4, 146.3 (2C), 146.2, 146.1, 146.08, 145.97 (2C), 145.92, 145.8, 145.7, 145.6, 145.5, 145.14 (2C), 145.11, 145.09, 145.04, 144.95, 144.91, 144.89, 144.75, 144.73, 144.6, 144.5, 144.1, 142.9, 142.8, 142.7, 142.53, 142.49, 142.47, 142.2, 142.18, 142.17, 142.11, 142.0, 141.88, 141.86, 141.84, 141.81, 141.76, 141.2, 140.9, 139.7, 139.5, 139.4, 139.37, 138.9, 138.02 (2C), 137.6, 136.2, 135.6, 131.73, 131.7, 130.7, 128.3 (2C), 127.9, 127.3, 126.9 (2C), 123.4, 113.1, 97.3 (sp3-C of C60), 76.1 (sp3-C of C60), 65.6, 28.3, 22.4; FT-IR (KBr) ν/cm−1: 2954, 2922, 2851, 1730, 1631, 1508, 1462, 1384, 1262, 1074, 619, 526; UV−vis (CHCl3) λ/(nm): 213, 221, 262, 429; HRMS (MALDI-TOF) m/z calcd for C77H1779BrO2 [M−] 1052.0417, found 1052.0409. Compound 5h. According to the general procedure, the reaction of 4c (10.0 mg, 0.01 mmol), p-toluenesulfonic acid (31.0 mg, 15 equiv), and a mixture of 1,4-dioxane-CS2-MeOH (16 mL:8 mL:8 mL) at 100 °C for 24 h afforded 5h (6.6 mg, 65%) as a brown amorphous solid along with unreacted fullerenol 4c (1.4 mg, 14%) after purification by column chromatography; 1H NMR (600 MHz, CS2/CDCl3) δ 8.15− 8.13 (m, 1H), 7.74−7.72 (m, 1H), 7.61−7.59 (m, 2H), 3.51 (s, 3H), 1.95 (s, 3H), 1.60 (s, 3H); 13C NMR (150 MHz, CS2/CDCl3, all 1C unless indicated) δ 155.0, 154.1, 151.2, 149.1, 147.9, 147.3, 146.38, 146.32, 146.28, 146.2, 146.09, 146.08, 145.97, 145.93, 145.89, 145.85, 145.74, 145.71, 145.4 (2C), 145.1 (2C), 145.08, 145.05, 144.92, 144.91, 144.9, 144.85, 144.8, 144.7, 144.6, 144.1, 142.88, 142.87, 142.7, 142.54, 142.51, 142.46, 142.2, 142.18, 142.15, 142.03, 142.01 (2C), 141.9, 141.7, 141.3, 141.2, 139.7, 139.49 (2C), 139.48 (2C), 139.4, 138.9, 137.7, 137.5, 136.2, 135.01, 135.0, 130.4, 128.69, 128.66, 127.6, 113.2, 97.2 (sp3-C of C60), 76.2 (sp3-C of C60), 51.8, 28.2, 22.2; FT-IR (KBr) ν/cm−1: 2923, 2852, 1631, 1488, 1384, 1264, 1168, 1089, 1003, 943, 826, 524; UV−vis (CHCl3) λ/(nm): 257, 313, 429; 681

DOI: 10.1021/acs.joc.7b02620 J. Org. Chem. 2018, 83, 672−683

Article

The Journal of Organic Chemistry HRMS (MALDI-TOF) m/z calcd for C71H1335ClO2 [M+] 932.0599, found 932.0576. Compound 5i. According to the general procedure, the reaction of 4c (10.0 mg, 0.01 mmol), p-toluenesulfonic acid (31.0 mg, 15 equiv), and a mixture of 1,4-dioxane-CS2-EtOH (16 mL:8 mL:8 mL) at 100 °C for 36 h afforded 5i (6.2 mg, 60%) as a brown amorphous solid along with unreacted fullerenol 4c (2.0 mg, 20%) after purification by column chromatography; 1H NMR (600 MHz, CS2/CDCl3) δ 8.12− 8.10 (m, 1H), 7.70−7.68 (m, 1H), 7.56−7.54 (m, 2H), 4.09 (dq, J = 9.5, 7.0 Hz, 1H), 3.51 (dq, J = 9.5, 7.0 Hz, 1H), 1.98 (s, 3H), 1.59 (s, 3H), 1.36 (t, J = 7.0 Hz, 3H); 13C NMR (150 MHz, CS2/CDCl3, all 1C unless indicated) δ 155.2, 154.1, 151.1, 149.2, 147.9, 147.2, 146.4 (2C), 146.3, 146.2, 146.1 (2C), 145.95, 145.92, 145.86, 145.83, 145.78, 145.7, 145.5, 145.1, 145.09, 145.07 (2C), 145.01, 144.9, 144.88, 144.86 (2C), 144.75, 144.63, 144.55, 144.1 (2C), 142.87, 142.86, 142.6, 142.53, 142.49, 142.45, 142.2, 142.16, 142.15, 142.01, 141.98, 141.87, 141.86, 141.7 (2C), 141.2, 141.0, 139.7, 139.5, 139.43, 139.37, 138.8, 137.64, 137.59, 136.1 (2C), 135.4, 134.9, 130.2, 128.6, 128.56, 127.4, 112.7, 97.1 (sp3-C of C60), 76.3 (sp3-C of C60), 59.1, 28.2, 22.2, 14.4; FT-IR (KBr) ν/cm−1: 2923, 2852, 1632, 1463, 1384, 1263, 1074, 965, 825, 765, 619, 526; UV−vis (CHCl3) λ/(nm): 257, 314, 429; HRMS (MALDI-TOF) m/z calcd for C72H1535ClO2 [M+] 946.0755, found 946.0714.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b02620. NMR spectra of compounds 2a−f, 4a−g, 5a−i, and CV of 2a−f (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Bo Jin: 0000-0002-6966-2876 Author Contributions

Y.-T.Y. and W.G. contributed equally to this work and should be considered co-first authors. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for financial support from the National Natural Science Foundation of China (51372211), the Open Project of State Key Laboratory Cultivation Base for Nonmetal Composites and Functional (project no. 14tdfk05), and the Institute of Materials, China Academy of Engineering Physics (project no. 16zh0142).

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REFERENCES

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DOI: 10.1021/acs.joc.7b02620 J. Org. Chem. 2018, 83, 672−683

Article

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DOI: 10.1021/acs.joc.7b02620 J. Org. Chem. 2018, 83, 672−683