Copper-Promoted Synthesis of 2-Fulleropyrrolines via

Sep 13, 2017 - The 13C NMR spectra of 2a and 2d–m exhibited no more than 29 peaks in the range of 135–150 ppm for the 58 sp2-carbons of the fuller...
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Cite This: J. Org. Chem. 2017, 82, 10823-10829

Copper-Promoted Synthesis of 2‑Fulleropyrrolines via Heteroannulation of [60]Fullerene with α‑Amino Ketones Sheng-Peng Jiang,† Qing-Hua Wu,† and Guan-Wu Wang*,†,‡ †

CAS Key Laboratory of Soft Matter Chemistry, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Hefei National Laboratory for Physical Sciences at Microscale, and Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, P.R. China ‡ State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou, Gansu 730000, P.R. China S Supporting Information *

ABSTRACT: A Cu(OAc)2-promoted heteroannulation of [60]fullerene with α-amino ketones has been exploited for the efficient synthesis of 2-fulleropyrrolines containing a trisubstituted or tetrasubstituted CC bond via the formation of C−C and C−N bonds. Mechanistic study indicates that a radical process should be involved in this transformation. Furthermore, theoretical computations show that the process via the attack of the carbon radical generated from the employed αamino ketone to [60]fullerene should be the preferred pathway. The electrochemical properties of the synthesized 2fulleropyrrolines have also been investigated.

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of C60 with aldehydes and primary amines.7h It should be noted that the unsubstituted position is located at the C2 of the pyrroline moiety. The synthesis of 2-fulleropyrrolines with unsubstituted position located at the C3 of the pyrroline moiety has never been reported until now. The unsubstituted olefinic carbon of the pyrroline moiety has the potential to undergo postfunctionalizations. Recently, we disclosed the synthesis of 1-fulleropyrrolines from the reaction of C60 and ketoxime acetates in the presence of CuBr and NaHSO3.7f As a part of our continuing interest in the Cu(I)/Cu(II)-catalyzed/ promoted reactions of C60,7a,f herein we describe a facile and efficient protocol to construct 2-fulleropyrrolines containing a trisubstituted or tetrasubstituted CC bond by the Cu(OAc)2promoted heteroannulation of C60 with α-amino ketones.

INTRODUCTION Owing to their huge potential applications in materials, biology, and nanoscience, a diversity of fullerene derivatives have been synthesized through different types of reactions over the past two decades.1 Free radical reaction, one of the first investigated reactions of fullerenes, represents the most powerful and straightforward protocol for the construction of diversified fullerene derivatives.2 Particularly, in recent years, transitionmetal-catalyzed/promoted radical reactions exhibit excellent ability to create novel functionalized fullerenes, attributed to their remarkable advantages such as high compatibility with a wide range of functional groups.2b−e The transition metals such as Mn(III),3 Fe(II)/Fe(III),4 Co(0),5 Ni(0),6 Cu(I)/Cu(II),7 Ag(I),8 and Pb(IV)9 have been continuously utilized to functionalize fullerenes due to their ready availability, cheap price, and ease of manipulation. Despite these advances, further exploration and development of new transition-metal-catalyzed/promoted synthetic methodologies still remain highly demanded for the construction of structurally diversified fullerene derivatives. The synthesis of C60-fused pyrroline derivatives containing a nitrogen atom bonded directly to the fullerene skeleton has rarely been reported. In 2006, our group first realized the synthesis of 2-fulleropyrrolines via the Mn(OAc)3-mediated reaction of C60 with β-enamino carbonyl compounds.3b Subsequently, Yang’s group described the preparation of 2fulleropyrrolines through the reaction of C60 with amines and dimethyl acetylenedicarboxylate (DMAD) in the presence of CuCl2.7d Nevertheless, the above-mentioned approaches only led to the formation of 2-fulleropyrrolines with a tetrasubstituted CC bond. More recently, the Li group successfully developed the synthesis of 2-fulleropyrrolines with a trisubstituted CC bond through the Cu(OAc)2-mediated reaction © 2017 American Chemical Society

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RESULTS AND DISCUSSION In the initial investigation, α-phenylamino propiophenone (1a) was chosen as a representative substrate to react with C60 for the desired heteroannulation. Encouraged by our previous work on the CuBr-mediated reaction of C60,7f we started the reaction of C60 (0.05 mmol) with 1a (2 equiv) by using CuBr as the initiator (2 equiv) in anhydrous chlorobenzene (CB) at 130 °C under an open-air atmosphere (Table 1, entry 1). Unfortunately, we did not observe any desired product. Then, different copper salts were investigated to induce the reaction. To our disappointment, neither Cu(I) salts such as CuCl, CuI, and Cu2O nor Cu(II) salts including CuBr2, CuCl2, CuCl2·2H2O, and CuO could promote the reaction (Table 1, entries 2−8). When Cu(OTf)2 was employed, only a trace amount of 2a was observed (Table 1, entry 9). Gratifyingly, a dramatic enhanceReceived: May 19, 2017 Published: September 13, 2017 10823

DOI: 10.1021/acs.joc.7b01237 J. Org. Chem. 2017, 82, 10823−10829

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The Journal of Organic Chemistry Table 1. Optimization for the Reaction of C60 with 1aa

entry

additive

molar ratiob

yield of 2a (%)c

1 2 3 4 5 6 7 8 9 10 11 12d 13e 14f 15g 16 17 18 19

CuBr CuCl CuI Cu2O CuBr2 CuCl2 CuCl2·2H2O CuO Cu(OTf)2 Cu(OAc)2·H2O Cu(OAc)2 Cu(OAc)2·H2O Cu(OAc)2·H2O Cu(OAc)2·H2O Cu(OAc)2·H2O Cu(OAc)2·H2O Cu(OAc)2·H2O Cu(OAc)2·H2O Cu(OAc)2·H2O

1:2:2 1:2:2 1:2:2 1:2:2 1:2:2 1:2:2 1:2:2 1:2:2 1:2:2 1:2:2 1:2:2 1:2:2 1:2:2 1:2:2 1:2:2 1:1:2 1:3:2 1:2:1 1:2:3

0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) trace (trace) 34 (81) 32 (67) 28 (80) 29 (53) 27 (64) 28 (62) 19 (61) 35 (65) 27 (50) 25 (54)

Unless otherwise noted, the reactions were performed in anhydrous CB (6 mL) at 130 °C under an open-air atmosphere for 5 h. bMolar ratio refers to C60/1a/additive. cIsolated yields. Values in parentheses were based on the consumed C60. dThe reaction was performed at 120 °C. eThe reaction was performed at 140 °C. fThe reaction time was 3 h. gThe reaction time was 7 h. a

ment in the product yield (34%) was obtained in the presence of Cu(OAc)2·H2O (Table 1, entry 10). When anhydrous Cu(OAc)2 was used as the promoter, a slightly lower yield of 2a (32%) was achieved (Table 1, entry 11 vs entry 10). Due to its cheap price and insensitivity to air and moisture as well as the higher product yield based on the consumed C60, Cu(OAc)2· H2O was selected to be the optimal promoter. The yield of the anticipated product 2a was lowered slightly to 28% upon decreasing the reaction temperature from 130 to 120 °C (Table 1, entry 12). Likewise, it was not beneficial to the reaction efficiency by raising the reaction temperature to 140 °C (Table 1, entry 13). Other reaction parameters including reaction time and the amounts of 1a and Cu(OAc)2·H2O were also systematically varied. It was found that reducing or increasing the reaction time could not improve the product yield of 2a, giving the desired product in 27 and 28% yields, respectively (Table 1, entries 14 and 15). When 1.0 equiv of 1a was used, the yield of 2a dropped significantly to 19% (Table 1, entry 16). A nearly same yield (35%) was obtained in the presence of 3.0 equiv of 1a (Table 1, entry 10 vs entry 17). The change of the amount of Cu(OAc)2·H2O could not provide a better result (Table 1, entries 18 and 19). Thus, the optimized reaction conditions were determined as follows: C60 (0.05 mmol), 2 equiv of 1a, and 2 equiv of Cu(OAc)2·H2O in CB (6 mL) at 130 °C for 5 h under an open-air atmosphere. We next turned our attention to explore the substrate scope of this protocol under the optimized conditions. As shown in Table 2, the reaction of α-arylamino propiophenones bearing both electron-donating groups and electron-withdrawing groups on the aryl ring proceeded efficiently under the optimal conditions and furnished the corresponding 2-fulleropyrrolines

in 31−40% yields. 1-Phenyl-2-(o-tolylamino)propan-1-one 1b gave a yield slightly higher than that of the meta- and paramethyl-substituted substrates 1c and 1d, indicating that the reaction was not sensitive to the steric effect of the N-aryl moiety. Compared with substrate 1e with a strong electron-rich methoxy (OMe) substituent and substrates 1b−d with a methyl group on the phenyl ring, substrate 1f bearing an electronwithdrawing group (Cl) showed a comparable reactivity, suggesting that the electronic effect of the substituent at the N-aryl ring had little influence on the reaction efficiency. The chloro atom was inert under our employed conditions, thus the chloro-containing product may be further manipulated and provide new functionalized products. The transformation of a 3,5-dimethyl-substituted substrate 1g occurred well and gave the desired product 2g in a higher yield (40%). When 2-((3,5dimethylphenyl)amino)-1-(p-tolyl)propan-1-one 1h was employed as the substrate to react with C60, the reaction proceeded smoothly to generate the desired product 2h in 37% yield. To our delight, the N-alkyl-substituted α-amino ketone 1i was also compatible with this protocol, affording product 2i in 17% yield. It should be noted that the butyrophenone analogues 1j and 1k were applicable, and the increase of the amounts of Cu(OAc)2·H2O, 1j, and 1k to 3 equiv was necessary to provide synthetically valuable yields of 18 and 22% for 2j and 2k, respectively. Gratifyingly, when substrates with R3 as an aryl group such as 1l and 1m were used, their reactivity increased obviously, providing the corresponding products 2l and 2m in 40 and 43% yields, respectively. The structures of products 2a−m were fully characterized by HRMS (ESI or MALDI-TOF), 1H NMR, 13C NMR, FT-IR, 10824

DOI: 10.1021/acs.joc.7b01237 J. Org. Chem. 2017, 82, 10823−10829

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The Journal of Organic Chemistry Table 2. Results for the Reaction of C60 with α-Amino Ketones 1a−m Promoted by Cu(OAc)2·H2Oa,b

ppm in the 13C NMR spectra, as well as the stretching vibrations at 1592−1601 cm−1 in the IR spectra demonstrated the existence of the CC−H group. The chemical shifts for the carbonyl group attached to the pyrrolines moiety appeared at 186.6−189.6 ppm. In the IR spectra, the strong absorption at 1646−1669 cm−1 also confirmed the presence of the carbonyl group. The structural assignment was further confirmed by the HSQC and HMBC spectra using 2a as a representative example. The HSQC spectrum of 2a displayed that the proton at 6.55 ppm had a correlation with the olefinic carbon at 114.7 ppm, proving that the proton was attached to the CC group. The HMBC spectrum of 2a showed that the proton at 6.55 ppm was correlated with two sp3-carbons of C60 at 75.0 and 90.1 ppm, one carbon at 147.8 ppm, as well as the carbonyl carbon at 187.3 ppm. These 2D NMR results were fully consistent with that 2a had a structure of 2-fulleropyrroline. Their UV−vis spectra showed a peak at 426−429 nm, which is the characteristic absorption for a 1,2-adduct of C60. In order to gain insight into the reaction mechanism, some control experiments were subsequently performed (Scheme 1). Scheme 1. Control Experiments

a

Unless otherwise noted, the reactions were performed with C60 (0.05 mmol), 1 (0.10 mmol), Cu(OAc)2·H2O (0.10 mmol) in anhydrous CB at 130 °C. bIsolated yields. Values in parentheses were based on the consumed C60. cC60 (0.05 mmol), 1 (0.15 mmol), Cu(OAc)2·H2O (0.15 mmol).

and UV−vis spectra. All HRMS of these products gave the correct [M + H]+ or [M]+ peaks. Their 1H NMR spectra displayed the expected chemical shifts as well as the splitting patterns for all protons. The 13C NMR spectra of 2a and 2d−m exhibited no more than 29 peaks in the range of 135−150 ppm for the 58 sp2-carbons of the fullerene cage and two peaks at 74−79 and 88−91 ppm for the two sp3-carbons of the fullerene skeleton, consistent with their Cs symmetry. In the 13C NMR spectra of 2b and 2c, there were more than 39 peaks in the range of 135−150 ppm with some overlapping ones for the 58 sp2-carbons of the fullerene cage and two peaks at 74−75 and 90−91 ppm for the two sp3-carbons of the fullerene skeleton, consistent with their C1 symmetry due to the unsymmetrical nature of N-aryl moiety in 2b and 2c. The chemical shifts at 74−79 and 88−91 ppm for the two sp3-carbons of the fullerene skeleton were close to the reported data of other fullerene derivatives with a nitrogen atom and a carbon atom attached to the fullerene skeleton.3b,7d−f,h The singlets at 5.90−6.56 ppm in 1 H NMR spectra, the signals at 108.9−119.6 and 147.2−148.5

When 2 equiv of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was added as a free radical scavenger into the reaction system under the standard conditions, the reaction was suppressed to a great extent, and the desired product 2a was obtained in only 4% yield. In the presence of another free radical scavenger, 2,6-di-tert-butyl-4-methylphenol (BHT), the formation of 2a was also severely inhibited, giving 2a in 6% yield. These results implied that this reaction might proceed through a radical pathway. In addition, the oxidative product 3a could be isolated in 67% yield by treating 1a with Cu(OAc)2· H2O. The use of 3a instead of 1a to react with C60 under the optimized conditions proceeded well and afforded the desired product 2a in 32% yield, which was nearly the same as that for the reaction of C60 with 1a. This result indicated that 3a should be the intermediate for the heteroannulation reaction. Based on the above results and previous reports on the copper-promoted radical reactions, a plausible mechanism for the formation of 2-fulleropyrrolines 2a−m is proposed and 10825

DOI: 10.1021/acs.joc.7b01237 J. Org. Chem. 2017, 82, 10823−10829

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The Journal of Organic Chemistry depicted in Scheme 2. This transformation is initiated via oxidation of 1 by CuII to afford the imine intermediate 3.

Scheme 3. Computational Results at the UB3LYP/6-31G(d) Level

Scheme 2. Proposed Reaction Mechanism for the Formation of 2

Table 3. Half-Wave Reduction Potentials of 2a−m and C60a

Tautomerization of the imine intermediate 3 gives the enamine 4, which can be transformed to the imino radical A through homolysis of the N−Cu bond of the formed CuII complex. The fullerenyl radical B can be produced after capture of the imino radical A by C60 and then undergoes cyclization to generate radical C. Subsequently, the radical C is converted to 2 by oxidation with a CuII species accompanied by proton elimination (path a). Alternatively, tautomerization of A can also give D, which attacks C60 to afford fullerenyl radical E. The cyclization of E generates the same radical C (path b). To determine the preferred reaction pathway toward the formation of the radical C, computational study for the reaction of C60 with 1a at the UB3LYP/6-31G(d) level with the Gaussian 09 program10 was performed, and the energy profiles are depicted in Scheme 3. Although the energy of the radical intermediate A-1a is the same as that of D-1a, the formation of the fullerenyl radical B-1a requires an activation energy of 19.6 kcal/mol, 12.2 kcal/mol higher than that for the formation of E-1a. Furthermore, the fullerenyl radical E-1a is more stable than B-1a by 16.8 kcal/mol. Therefore, the product formation via D-1a should be more favorable (path b), even though the activation energy required to produce C-1a from E-1a is slightly higher than that from B-1a. The half-wave reduction potentials of products 2a−m along with those of C60 have been investigated by cyclic voltammetry (CV), and their half-wave potentials are summarized in Table 3. All of their electrochemical properties were quite similar and showed two reversible redox processes. As shown in Table 3, the first reduction potentials of 2-fulleropyrrolines 2a−m were more negative than that of C60, indicating that they possess LUMO energy levels higher than that of C60 and may have

compound

E1

E2

C60 2a 2b 2c 2d 2e 2f 2g 2h 2i 2jb 2k 2l 2m

−1.080 −1.130 −1.128 −1.128 −1.132 −1.135 −1.124 −1.141 −1.130 −1.146 −1.137 −1.144 −1.098 −1.123

−1.473 −1.510 −1.517 −1.517 −1.515 −1.522 −1.530 −1.527 −1.503 −1.531 −1.522 −1.534 −1.474 −1.513

a

Versus ferrocene/ferrocenium. Experimental conditions: 1 mM of 2a−m/C60 and 0.1 M of n-Bu4NClO4 in anhydrous ODCB; reference electrode: SCE; working electrode: Pt; auxiliary electrode: Pt wire; scanning rate: 20 mV s−1. bSaturated solution.

potential application in organic photovoltaic devices as acceptors.11

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CONCLUSIONS In summary, we have successfully disclosed a Cu(OAc)2promoted heteroannulation reaction of [60]fullerene with αamino ketones for the efficient construction of a series of 2fullereropyrrolines containing a trisubstituted or tetrasubstituted CC bond via the formation of C−C and C−N bonds. Control experiments and theoretical calculations revealed that the process via the attack of the carbon radical species generated from the employed α-amino ketone to [60]fullerene should be a preferred pathway for the formation of 2fulleropyrrolines. The electrochemistry of the synthesized 2fulleropyrrolines has also been explored.

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EXPERIMENTAL SECTION

General Procedure for the Synthesis of 2a−m from the Cu(OAc)2·H2O-Promoted Reaction of C60 with 1a−m. A mixture of C60 (0.05 mmol), α-amino ketones 1 (0.10 mmol), and Cu(OAc)2· H2O (0.10 mmol) was dissolved in CB (6 mL). Then the solution was vigorously stirred at 130 °C and stopped at the designated time. The solvent was evaporated in vacuo, and the residue was directly separated 10826

DOI: 10.1021/acs.joc.7b01237 J. Org. Chem. 2017, 82, 10823−10829

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The Journal of Organic Chemistry

cm−1 (KBr) 2918, 2857, 1661, 1599, 1510, 1428, 1378, 1270, 1232, 1175, 1110, 1009, 904, 807, 709, 570, 525; UV−vis (CHCl3) λmax/nm (log ε) 257 (5.06), 325 (4.49), 428 (3.48); HRMS (ESI-FT-ICR) m/z calcd for C76H14NO [M + H]+ 956.1070, found 956.1054. Fulleropyrroline 2e. By following the general procedure, the reaction of C60 (36.1 mg, 0.05 mmol) with 1e (23.0 mg, 0.10 mmol) and Cu(OAc)2·H2O (19.6 mg, 0.10 mmol) at 130 °C for 3 h afforded recovered C60 (17.4 mg, 48%) and 2e (16.5 mg, 34%) with CS2/ CH2Cl2 (5:1, v/v) as the eluent for silica gel column purification: amorphous brown solid; 1H NMR (400 MHz, CS2/CDCl3 (3:1 v/v)) δ 8.28 (d, J = 7.2 Hz, 2H), 7.62 (t, J = 7.3 Hz, 1H), 7.53 (t, J = 7.6 Hz, 2H), 7.48 (d, J = 8.8 Hz, 2H), 6.79 (d, J = 8.8 Hz, 2H), 6.50 (s, 1H), 3.72 (s, 3H); 13C NMR (100 MHz, CS2/CDCl3 (3:1 v/v)) δ 187.3, 158.0, 149.2, 148.0, 147.7, 147.2, 146.1, 146.0, 145.9, 145.8, 145.6, 145.3, 145.1, 145.0, 144.9, 144.8, 144.3, 144.1, 142.9, 142.6, 142.5, 142.10, 142.07, 141.7, 140.6, 139.5, 136.8, 136.1, 136.0, 135.8, 133.3, 129.52, 129.47, 128.4, 114.6, 113.0, 90.4 (sp3-C of C60), 74.8 (sp3-C of C60), 54.9; FT-IR ν/cm−1 (KBr) 2922, 2834, 1658, 1600, 1504, 1434, 1369, 1240, 1171, 1103, 1032, 1002, 702, 565, 523; UV−vis (CHCl3) λmax/nm (log ε) 256 (5.06), 326 (4.49), 428 (3.48); HRMS (MALDITOF) m/z calcd for C76H13NO2 [M]+ 971.0941, found 971.0927. Fulleropyrroline 2f. By following the general procedure, the reaction of C60 (36.0 mg, 0.05 mmol) with 1f (25.6 mg, 0.10 mmol) and Cu(OAc)2·H2O (20.2 mg, 0.10 mmol) at 130 °C for 5 h afforded recovered C60 (17.8 mg, 49%) and 2f (14.9 mg, 31%): amorphous brown solid; 1H NMR (400 MHz, CS2 with DMSO-d6 as the external reference) δ 8.21−8.16 (m, 2H), 7.58 (tt, J = 7.3, 1.3 Hz, 1H), 7.51−7.46 (m, 2H), 7.43 (d, J = 8.7 Hz, 2H), 7.19 (d, J = 8.7 Hz, 2H), 6.49 (s, 1H); 13C NMR (100 MHz, CS2/CDCl3 (3:1 v/v)) δ 186.6, 148.7, 147.7, 147.19, 147.17, 146.03, 145.96, 145.8, 145.74, 145.66, 145.6, 145.1, 145.0, 144.7, 144.24, 144.21, 144.0, 142.6, 142.5, 142.4, 142.0, 141.9, 141.8, 141.68, 141.65, 140.6, 139.5, 136.6, 136.2, 135.7, 133.3, 132.6, 129.5, 129.4, 129.0, 128.5, 115.1, 89.8 (sp3-C of C60), 74.9 (sp3-C of C60); FT-IR ν/cm−1 (KBr) 2919, 1654, 1497, 1435, 1374, 1229, 1171, 1092, 1010, 702, 522; UV−vis (CHCl3) λmax/ nm (log ε) 258 (5.14), 328 (4.60), 429 (3.51); HRMS (ESI-FT-ICR) m/z calcd for C75H11NO35Cl [M + H]+ 976.0524, found 976.0525. Fulleropyrroline 2g. By following the general procedure, the reaction of C60 (35.9 mg, 0.05 mmol) with 1g (25.6 mg, 0.10 mmol) and Cu(OAc)2·H2O (20.0 mg, 0.10 mmol) at 130 °C for 3 h afforded recovered C60 (18.1 mg, 50%) and 2g (19.4 mg, 40%): amorphous brown solid; 1H NMR (400 MHz, CS2/CDCl3 (3:1 v/v)) δ 8.31−8.24 (m, 2H), 7.61 (tt, J = 7.3, 1.3 Hz, 1H), 7.56−7.49 (m, 2H), 7.16 (s, 2H), 6.75 (s, 1H), 6.50 (s, 1H), 2.22 (s, 6H); 13C NMR (100 MHz, CS2/CDCl3 (3:1 v/v)) δ 187.7, 149.3, 148.1, 147.8, 147.3, 146.2, 146.1, 146.0, 145.93, 145.88, 145.7, 145.5, 145.2, 145.12, 145.09, 144.9, 144.8, 144.4, 144.2, 143.3, 143.0, 142.7, 142.63, 142.60, 142.22, 142.20, 141.83, 141.80, 140.7, 139.5, 139.0, 136.9, 136.2, 135.9, 133.4, 129.6, 128.6, 128.5, 125.7, 114.3, 90.2 (sp3-C of C60), 75.1 (sp3-C of C60), 21.4; FT-IR ν/cm−1 (KBr) 2914, 2855, 1660, 1593, 1512, 1434, 1375, 1244, 1170, 1107, 1047, 1005, 904, 732, 564, 525; UV−vis (CHCl3) λmax/nm (log ε) 257 (5.05), 324 (4.53), 428 (3.50); HRMS (ESI-FT-ICR) m/z calcd for C77H16NO [M + H]+ 970.1226, found 970.1211. Fulleropyrroline 2h. By following the general procedure, the reaction of C60 (35.9 mg, 0.05 mmol) with 1h (26.6 mg, 0.10 mmol) and Cu(OAc)2·H2O (19.7 mg, 0.10 mmol) at 130 °C for 3 h afforded recovered C60 (17.1 mg, 48%) and 2h (18.0 mg, 37%): amorphous brown solid; 1H NMR (400 MHz, CS2/CDCl3 (3:1 v/v)) δ 8.18 (d, J = 8.1 Hz, 2H), 7.31 (d, J = 8.1 Hz, 2H), 7.14 (s, 2H), 6.73 (s, 1H), 6.45 (s, 1H), 2.47 (s, 3H), 2.22 (s, 6H); 13C NMR (100 MHz, CS2/ CDCl3 (3:1 v/v)) δ 186.6, 149.2, 148.0, 147.7, 147.2, 146.05, 145.98, 145.85, 145.82, 145.7, 145.6, 145.4, 145.04, 144.97, 144.8, 144.7, 144.3, 144.04, 143.96, 143.2, 142.9, 142.6, 142.5, 142.1, 141.71, 141.67, 140.6, 139.3, 138.8, 136.1, 135.8, 134.3, 129.8, 129.1, 128.4, 125.6, 113.2, 90.0 (sp3-C of C60), 75.0 (sp3-C of C60), 21.9, 21.4; FTIR ν/cm−1 (KBr) 2915, 2858, 1662, 1601, 1513, 1462, 1428, 1346, 1304, 1258, 1172, 1109, 1042, 1002, 841, 783, 729, 564, 526; UV−vis (CHCl3) λmax/nm (log ε) 257 (5.15), 328 (4.64), 428 (3.61); HRMS

on a silica gel column with CS2/CH2Cl2 (10:1 v/v unless specified) as the eluent to give recovered C60 and then the desired product 2. Caution: in order to avoid the decomposition of 2 induced by light, the used glassware should be wrapped with aluminum foil during the workup procedure including separation on a silica gel column and subsequent evaporation in vacuo. Fulleropyrroline 2a. By following the general procedure, the reaction of C60 (35.9 mg, 0.05 mmol) with 1a (22.2 mg, 0.10 mmol) and Cu(OAc)2·H2O (19.7 mg, 0.10 mmol) at 130 °C for 5 h afforded recovered C60 (20.8 mg, 58%) and 2a (15.7 mg, 34%): amorphous brown solid; 1H NMR (400 MHz, CS2/CDCl3 (3:1 v/v)) δ 8.27 (d, J = 7.3 Hz, 2H), 7.61 (t, J = 7.4 Hz, 1H), 7.56 (d, J = 8.0 Hz, 4H), 7.52 (t, J = 7.6 Hz, 2H), 7.28 (t, J = 7.8 Hz, 2H), 7.14 (t, J = 7.4 Hz, 1H), 6.56 (s, 1H); 13C NMR (100 MHz, CS2/CDCl3 (3:1 v/v)) δ 187.3, 149.1, 147.8, 147.3, 146.11, 146.05, 145.9, 145.8, 145.7, 145.3, 145.1, 145.0, 144.8, 144.6, 144.4, 144.1, 143.4, 143.0, 142.64, 142.57, 142.5, 142.12, 142.10, 141.8, 140.6, 139.5, 136.8, 136.2, 135.9, 133.4, 129.6, 129.5, 128.5, 127.9, 126.6, 114.7, 90.1 (sp3-C of C60), 75.0 (sp3-C of C60); FT-IR ν/cm−1 (KBr) 2921, 2854, 1658, 1592, 1491, 1432, 1369, 1225, 1173, 1004, 696, 565, 524; UV−vis (CHCl3) λmax/nm (log ε) 257 (5.02), 323 (4.47), 428 (3.46); HRMS (ESI-FT-ICR) m/z calcd for C75H12NO [M + H]+ 942.0913, found 942.0902. Fulleropyrroline 2b. By following the general procedure, the reaction of C60 (35.9 mg, 0.05 mmol) with 1b (23.5 mg, 0.10 mmol) and Cu(OAc)2·H2O (19.8 mg, 0.10 mmol) at 130 °C for 5 h afforded recovered C60 (19.4 mg, 54%) and 2b (16.0 mg, 34%): amorphous brown solid; 1H NMR (400 MHz, CS2/CDCl3 (3:1 v/v)) δ 8.22−8.15 (m, 2H), 7.64−7.58 (m, 2H), 7.56−7.49 (m, 2H), 7.21−7.10 (m, 3H), 6.40 (s, 1H), 2.66 (s, 3H); 13C NMR (100 MHz, CS2/CDCl3 (3:1 v/ v)) δ 186.8, 149.6, 149.1, 148.5, 147.7, 147.3, 146.08, 146.05, 145.9, 145.82, 145.78, 145.61, 145.55, 145.2, 145.13, 145.11, 145.07, 145.03, 145.01, 144.98, 144.7, 144.4, 144.33, 144.31, 144.11, 144.08, 143.0, 142.61, 142.59, 142.56, 142.15, 142.13, 142.11, 142.10, 142.06, 142.0, 141.8, 141.7, 140.8, 140.6, 139.6, 139.4, 138.3, 137.1, 135.9, 135.8, 133.1, 131.8, 131.0, 129.6, 128.4, 127.9, 126.9, 112.4, 90.5 (sp3-C of C60), 75.0 (sp3-C of C60), 19.8; FT-IR ν/cm−1 (KBr) 2918, 2854, 1661, 1600, 1508, 1435, 1379, 1271, 1231, 1175, 1110, 1052, 1011, 902, 806, 706, 524; UV−vis (CHCl3) λmax/nm (log ε) 257 (5.15), 318 (4.61), 428 (3.57); HRMS (ESI-FT-ICR) m/z calcd for C76H14NO [M + H]+ 956.1070, found 956.1057. Fulleropyrroline 2c. By following the general procedure, the reaction of C60 (35.9 mg, 0.05 mmol) with 1c (23.7 mg, 0.10 mmol) and Cu(OAc)2·H2O (19.9 mg, 0.10 mmol) at 130 °C for 5 h afforded recovered C60 (20.6 mg, 57%) and 2c (15.8 mg, 33%): amorphous brown solid; 1H NMR (400 MHz, CS2/CDCl3 (3:1 v/v)) δ 8.22−8.17 (m, 2H), 7.65−7.59 (m, 2H), 7.56−7.49 (m, 2H), 7.21− 7.10 (m, 3H), 6.41 (s, 1H), 2.66 (s, 3H); 13C NMR (100 MHz, CS2/ CDCl3 (3:1 v/v)) δ 186.9, 149.5, 149.1, 148.4, 147.7, 147.3, 146.1, 146.0, 145.9, 145.79, 145.75, 145.6, 145.5, 145.14, 145.10, 145.06, 145.01, 144.99, 144.96, 144.7, 144.4, 144.30, 144.29, 144.08, 144.06, 142.96, 142.93, 142.59, 142.56, 142.5, 142.12, 142.11, 142.08, 142.03, 142.02, 141.74, 141.71, 140.8, 140.6, 139.5, 139.4, 138.2, 137.1, 135.9, 135.8, 133.2, 131.8, 130.9, 129.6, 128.4, 127.9, 112.6, 90.5 (sp3-C of C60), 75.0 (sp3-C of C60), 19.8; FT-IR ν/cm−1 (KBr) 2919, 1657, 1593, 1491, 1434, 1371, 1263, 1227, 1174, 1109, 1049, 1005, 706, 565, 525; UV−vis (CHCl3) λmax/nm (log ε) 258 (5.09), 327 (4.53), 428 (3.52); HRMS (MALDI-TOF) m/z calcd for C76H13NO [M]+ 955.0992, found 955.0979. Fulleropyrroline 2d. By following the general procedure, the reaction of C60 (35.9 mg, 0.05 mmol) with 1d (23.8 mg, 0.10 mmol) and Cu(OAc)2·H2O (19.9 mg, 0.10 mmol) at 130 °C for 5 h afforded recovered C60 (22.7 mg, 63%) and 2d (14.8 mg, 31%): amorphous brown solid; 1H NMR (400 MHz, CS2/CDCl3 (3:1 v/v)) δ 7.61−7.55 (m, 2H), 7.58 (tt, J = 7.4, 1.3 Hz, 1H), 7.42−7.37 (m, 2H), 7.40 (d, J = 8.2 Hz, 2H), 7.04 (d, J = 8.2 Hz, 2H), 6.47 (s, 1H), 2.27 (s, 3H); 13C NMR (100 MHz, CS2/CDCl3 (3:1 v/v)) δ 187.0, 149.1, 147.9, 147.7, 147.2, 146.1, 146.0, 145.9, 145.81, 145.77, 145.6, 145.4, 145.1, 145.0, 144.8, 144.7, 144.3, 144.1, 142.9, 142.6, 142.5, 142.1, 141.7, 140.8, 140.6, 139.4, 136.7, 136.3, 136.1, 135.8, 133.2, 130.1, 129.5, 128.4, 127.9, 113.7, 90.2 (sp3-C of C60), 74.9 (sp3-C of C60), 21.2; FT-IR ν/ 10827

DOI: 10.1021/acs.joc.7b01237 J. Org. Chem. 2017, 82, 10823−10829

Article

The Journal of Organic Chemistry

and Cu(OAc)2·H2O (29.5 mg, 0.15 mmol) at 130 °C for 3 h afforded recovered C60 (16.3 mg, 45%) and 2m (22.5 mg, 43%): amorphous brown solid; 1H NMR (400 MHz, CS2 with DMSO-d6 as the external reference) δ 8.25−8.16 (m, 2H), 7.54−7.44 (m, 3H), 7.39 (t, J = 7.5 Hz, 2H), 7.23−7.12 (m, 5H), 6.70 (s, 1H), 2.20 (s, 6H); 13C NMR (100 MHz, CS2 with DMSO-d6 as the external reference) δ 187.3, 148.2, 147.1, 146.6, 145.53, 145.47, 145.32, 145.29, 145.26, 145.22, 145.17, 145.0, 144.7, 144.5, 144.4, 143.8, 143.5, 142.9, 142.3, 142.05, 141.99, 141.8, 141.58, 141.55, 141.54, 141.3, 141.0, 139.6, 138.8, 138.2, 135.7, 135.5, 135.0, 132.6, 132.0, 130.3, 128.9, 128.1, 127.74, 127.69, 127.3, 126.2, 118.9, 89.0 (sp3-C of C60), 78.2 (sp3-C of C60), 20.8; FT-IR ν/cm−1 (KBr) 2911, 1667, 1593, 1511, 1447, 1327, 1221, 1165, 1005, 851, 831, 695, 563, 527; UV−vis (CHCl3) λmax/nm (log ε) 257 (5.07), 314 (4.54), 428 (3.55); HRMS (MALDI-TOF) m/z calcd for C83H19NO [M]+ 1045.1461, found 1045.1445. 1-Phenyl-2-(phenylimino)propan-1-one 3a. A mixture of 1a (22.4 mg, 0.10 mmol) and Cu(OAc)2·H2O (19.7 mg, 0.10 mmol) in CB (3 mL) was heated at 130 °C for 3 h. The reaction mixture was cooled to room temperature, and most of the solvent was evaporated in vacuo. The residue was purified by column chromatography (SiO2, PE/ EtOAc = 30:1) to afford 3a12 as colorless oil (14.9 mg, 67%): 1H NMR (400 MHz, CDCl3) δ 8.14 (d, J = 7.8 Hz, 2H), 7.59 (t, J = 7.4 Hz, 1H), 7.48 (t, J = 7.6 Hz, 2H), 7.39 (t, J = 7.8 Hz, 2H), 7.15 (t, J = 7.4 Hz, 1H), 6.86 (d, J = 7.8 Hz, 2H), 2.17 (s, 3H). Previous literature data for 3a: 1H NMR (300 MHz, CDCl3) δ 8.15 (dd, J = 8.4, 1.5 Hz, 2H), 7.60 (tt, J = 7.5, 1.5 Hz, 1H), 7.48 (dd, J = 8.4, 7.5 Hz, 2H), 7.39 (dd, J = 8.4, 7.2 Hz, 2H), 7.16 (tt, J = 7.2, 1.2 Hz, 1H), 6.86 (dd, J = 8.4, 1.2 Hz, 2H), 2.18 (s, 3H).12

(ESI-FT-ICR) m/z calcd for C78H18NO [M + H]+ 984.1383, found 984.1360. Fulleropyrroline 2i. By following the general procedure, the reaction of C60 (36.0 mg, 0.05 mmol) with 1i (28.6 mg, 0.15 mmol) and Cu(OAc)2·H2O (30.3 mg, 0.15 mmol) at 130 °C for 3 h afforded recovered C60 (15.9 mg, 44%) and 2i (7.7 mg, 17%): amorphous brown solid; 1H NMR (400 MHz, CS2/CDCl3 (3:1 v/v)) δ 8.36−8.28 (m, 2H), 7.68 (t, J = 7.3 Hz, 1H), 7.59 (t, J = 7.5 Hz, 2H), 5.90 (s, 1H), 4.79 (hept, J = 6.9 Hz, 1H), 1.61 (d, J = 6.9 Hz, 6H); 13C NMR (100 MHz, CS2/CDCl3 (3:1 v/v)) δ 189.6, 149.9, 148.4, 147.8, 147.3, 146.2, 146.01, 145.98, 145.9, 145.8, 145.7, 145.1, 145.02, 144.99, 144.9, 144.5, 144.1, 143.7, 143.1, 142.68, 142.66, 142.6, 142.4, 142.14, 142.13, 141.80, 141.79, 140.7, 139.6, 137.4, 136.4, 135.6, 133.6, 130.1, 128.6, 108.9, 89.9 (sp3-C of C60), 75.1 (sp3-C of C60), 50.3, 22.8; FT-IR ν/cm−1 (KBr) 2964, 2923, 2861, 1665, 1595, 1510, 1433, 1378, 1315, 1242, 1181, 1107, 994, 710, 565, 525; UV−vis (CHCl3) λmax/nm (log ε) 257 (5.13), 324 (4.54), 428 (3.68); HRMS (ESI-FT-ICR) m/z calcd for C72H14NO [M + H]+ 908.1070, found 908.1049. Fulleropyrroline 2j. By following the general procedure, the reaction of C60 (35.9 mg, 0.05 mmol) with 1j (35.9 mg, 0.15 mmol) and Cu(OAc)2·H2O (30.1 mg, 0.15 mmol) at 130 °C for 3 h afforded recovered C60 (22.3 mg, 62%) and 2j (8.6 mg, 18%): amorphous brown solid; 1H NMR (400 MHz, CS2 with DMSO-d6 as the external reference) δ 8.23 (d, J = 7.8 Hz, 2H), 7.58−7.44 (m, 3H), 7.44−7.35 (m, 2H), 7.22−7.12 (m, 2H), 7.06−6.98 (m, 1H), 2.54 (s, 3H) (it should be noted that the very low solubility of 2j prevented us f rom obtaining a 13C NMR spectrum with a good signal-to-noise ratio); FT-IR ν/cm−1 (KBr) 2926, 2863, 1660, 1631, 1593, 1510, 1488, 1448, 1430, 1342, 1300, 1221, 1176, 1106, 988, 746, 732, 711, 694, 576, 526; UV− vis (CHCl3) λmax/nm (log ε) 256 (5.05), 326 (4.49), 428 (3.50); HRMS (MALDI-TOF) m/z calcd for C76H13NO [M]+ 955.0992, found 955.0981. Fulleropyrroline 2k. By following the general procedure, the reaction of C60 (36.0 mg, 0.05 mmol) with 1k (39.5 mg, 0.15 mmol) and Cu(OAc)2·H2O (29.8 mg, 0.15 mmol) at 130 °C for 3 h afforded recovered C60 (18.8 mg, 52%) and 2k (10.8 mg, 22%): amorphous brown solid; 1H NMR (400 MHz, CS2/CDCl3 (3:1 v/v)) δ 8.28−8.23 (m, 2H), 7.50 (tt, J = 7.3, 1.3 Hz, 1H), 7.44−7.38 (m, 2H), 7.10−7.07 (m, 2H), 6.63−6.60 (m, 1H), 6.61 (s, 1H), 2.52 (s, 3H), 2.15 (s, 6H); 13 C NMR (100 MHz, CS2/CDCl3 (3:1 v/v)) δ 189.0, 148.8, 147.8, 147.3, 147.2, 146.08, 146.06, 145.9, 145.8, 145.7, 145.6, 145.5, 145.35, 145.28, 145.0, 144.9, 144.3, 144.2, 143.8, 142.9, 142.6, 142.5, 142.3, 142.14, 142.11, 142.06, 141.8, 141.6, 140.4, 139.3, 138.7, 136.6, 135.94, 135.88, 133.0, 129.4, 128.2, 128.1, 125.80, 118.8, 88.6 (sp3-C of C60), 76.8 (sp3-C of C60), 21.3, 12.7; FT-IR ν/cm−1 (KBr) 2921, 2858, 1646, 1593, 1507, 1437, 1339, 1229, 1170, 1052, 994, 700, 617, 563, 523; UV−vis (CHCl3) λmax/nm (log ε) 258 (5.03), 326 (4.42), 428 (3.40); HRMS (ESI-FT-ICR) m/z calcd for C78H18NO [M + H]+ 984.1383, found 984.1384. Fulleropyrroline 2l. By following the general procedure, the reaction of C60 (36.1 mg, 0.05 mmol) with 1l (45.0 mg, 0.15 mmol) and Cu(OAc)2·H2O (30.1 mg, 0.15 mmol) at 130 °C for 3 h afforded recovered C60 (16.9 mg, 47%) and 2l (20.6 mg, 40%): amorphous brown solid; 1H NMR (400 MHz, CS2 with DMSO-d6 as the external reference) δ 8.19 (d, J = 7.5 Hz, 2H), 7.56 (d, J = 8.2 Hz, 2H), 7.52 (d, J = 6.6 Hz, 2H), 7.48 (t, J = 7.3 Hz, 1H), 7.39 (t, J = 7.5 Hz, 2H), 7.27−7.15 (m, 5H), 7.10 (t, J = 7.4 Hz, 1H); 13C NMR (100 MHz, CS2 with DMSO-d6 as the external reference) δ 187.3, 148.2, 147.2, 146.7, 145.6, 145.5, 145.4, 145.33, 145.32, 145.29, 145.12, 145.08, 144.7, 144.6, 144.4, 143.8, 143.6, 142.7, 142.4, 142.11, 142.06, 141.8, 141.7, 141.64, 141.60, 141.3, 141.1, 139.6, 139.0, 135.7, 135.0, 132.8, 131.9, 130.4, 128.9, 128.4, 127.9, 127.8, 127.4, 126.3, 119.6, 89.0 (sp3-C of C60), 78.2 (sp3-C of C60); FT-IR ν/cm−1 (KBr) 2922, 2849, 1669, 1649, 1593, 1578, 1512, 1492, 1447, 1429, 1347, 1227, 1003, 766, 755, 744, 733, 698, 562, 527; UV−vis (CHCl3) λmax/nm (log ε) 256 (5.06), 313 (4.53), 426 (3.51); HRMS (MALDI-TOF) m/z calcd for C81H15NO [M]+ 1017.1148, found 1017.1136. Fulleropyrroline 2m. By following the general procedure, the reaction of C60 (36.1 mg, 0.05 mmol) with 1m (49.3 mg, 0.15 mmol)

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.joc.7b01237. NMR spectra of 2a−m and 3a, CVs of 2a−m, and computational results (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Guan-Wu Wang: 0000-0001-9287-532X 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 (Nos. 21572211 and 21132007). REFERENCES

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