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Cite This: J. Org. Chem. 2018, 83, 15268−15276

Tunable Copper-Catalyzed Reaction of C60 with 2‑Ethoxycarbonylacetamides and Subsequent BF3·Et2O‑Mediated Isomerization of the Generated Dihydrofuran-Fused Fullerenes to Fulleropyrrolidinones Qiaoqiao Teng,† Yi-Chen Tan,† Chun-Bao Miao, Xiao-Qiang Sun, and Hai-Tao Yang*

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Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, Advanced Catalysis and Green Manufacturing Collaborative Innovation Center, School of Petrochemical Engineering, Changzhou University, Changzhou 213164, China S Supporting Information *

ABSTRACT: A tunable copper-catalyzed reaction of C60 with 2-ethoxycarbonylacetamides using air as the oxidant has been explored, which selectively affords methanofullerenes (2) and dihydrofuran-fused fullerenes (3) under the CuI/DMAP and CuCl/NMI catalytic systems, respectively. Furthermore, the generated dihydrofuran-fused fullerenes could be transformed to fulleropyrrolidinones (4 and 5) upon treatment with BF3·Et2O.

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INTRODUCTION

Scheme 1. Experimental Conception

To date, a great diversity of reactions has been developed to functionalize fullerenes, and some of the derivatives have shown a wide range of attractive applications in materials1 and biomedical sciences.2 The exploration of new modification protocols for the preparation of more organofullerenes with novel architectures and properties is still required to expand their applications.3 Among the numerous research endeavors, free radical-mediated functionalization is a promising strategy, which is often initiated by transition metals.4 In this respect, our group has recently managed the addition of an N-centered radical to C60, which has been attracting less attention compared to the C/O-radical. By using the iodine/I2 system5 or Cu(I/II) reagents,6 a variety of nitrogen-containing heterocycle-fused C60 derivatives have been obtained via the respective reaction of C60 with amines/amides/amidines/ sulfonamides/sulfamides/ureas. Along this line, we herein extended the substrate of ureas to 2-ethoxycarbonylacetamides, in which one of the nucleophilic nitrogen atom was replaced by a C-centered nucleophilic atom, and envisioned that a similar reaction process might occur to generate the unprecedented fulleropyrrolidinones (Scheme 1). To the best of our knowledge, only one group has reported the synthesis of fulleropyrrolidinones through the reaction of C60 with amino acid esters and carbon disulfide followed by hydrolysis of the resulting C60-fused cyclic thioamides.7 © 2018 American Chemical Society

Different from the structure proposed here, the nitrogen atom was not directly bonded to the C60 cage therein.

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RESULTS AND DISCUSSION 2-Ethoxycarbonylacetanilide (1a) was chosen as a model substrate to react with C60 (Table 1). Under Cu(OAc)2/Phen conditions, which have been proven to promote the diamination of C60 with ureas efficiently,6d an unexpected methanofullerene 2a was isolated in 10% yield after reacting for 4 h at 140 °C (entry 1). The combination of CuI with Phen gave a similar result (entry 2). When DMAP was used instead of Phen, the reaction temperature could be reduced to 80 °C (entry 3). Moreover, we were pleased to find that catalytic amounts of CuI and DMAP could also realize the transformation by treating C60 with 2 equiv of 1a, 0.2 equiv of CuI, Received: October 3, 2018 Published: November 28, 2018 15268

DOI: 10.1021/acs.joc.8b02547 J. Org. Chem. 2018, 83, 15268−15276

Article

The Journal of Organic Chemistry Table 1. Screening of the Reaction Conditions

entry

additives

[C60/1a/additives]

T (°C)

t (h)

2a (%)a

3a (%)a

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Cu(OAc)2, Phen CuI, Phen CuI, DMAP CuI, DMAP CuI, DMAP CuCl, DMAP CuCl, NMI CuCl, NMI CuCl, NMI CuCl, NMI CuCl, NMI CuCl, NMI CuCl, Et3N CuCl, 2,6-lutidine CuCl, 2,2′-bipyridine CuCl, TMDEA

1:3:3:3 1:3:3:3 1:2:1:2 1:2:0.2:0.04 1:2:0.2:0.04 1:2:1:0.2 1:2:1:2 1:2:1:0.6 1:2:1:0.4 1:2:1:0.2 1:2:0.2:0.04 1:2:0.2:0.04 1:2:1:0.2 1:2:1:0.2 1:2:1:0.2 1:2:1:0.2

140 140 80 80 120 80 80 80 80 80 80 120 80 80 80 80

4 4 4 4 4 4 6 6 6 6 6 4 4 4 6 4

10 (59) 14 (64) 16 (79) 19 (81) 34 (77) trace nr 0 0 0 0 0 trace trace nr nr

0 0 0 0 0 5 (88) nr trace 9 (81) 27 (64) 26 (78) 29 (71) 9 (89) 16 (82) nr nr

a

Isolated yield; the values in parentheses are based on consumed C60.

and 0.04 equiv of DMAP at 80 °C for 4 h to deliver the 2a in 19% yield (entry 4). Increasing the temperature to 120 °C resulted in a significant improvement in yield (entry 5, 34%). It was worth noting that DMAP was crucial to the conversion because no reaction occurred in its absence. Upon changing the copper salts from CuI to CuCl, only a trace amount of 2a was observed by TLC and a new product of dihydrofuran-fused C60 3a was obtained in 5% yield (entry 6). Using NMI (N-methylimidazole) instead of DMAP improved the yield of 3a to 27% after reacting at 80 °C for 6 h (entry 10). It is somewhat odd to observe that the yield of 3a decreased notably with the increased molar ratio of NMI/ CuCl (entries 7−10). When the molar ratio reached 0.6, no product was even observed by TLC (entry 8). Similarly, the addition of only catalytic amounts of CuCl and NMI could also realize the transformation. Treating C60 with 2 equiv of 1a, 0.2 equiv of CuCl, and 0.04 equiv of NMI at 120 °C for 4 h afforded 2a in 29% yield (entry 12). If CuCl and NMI were premixed and stirred overnight in air and then C60 and 1a were added to react at 120 °C, no reaction occurred. So far, the reason was not clear. Although a comparable yield could be obtained at a lower temperature, the reaction proceeded slightly slower (entry 11). The combination of CuCl with Et3N or 2,6-lutidine gave much lower yields (entries 13 and 14). Using 2,2′-bipyridine or TMDEA instead of NMI resulted in complete failure of the reaction (entries 15 and 16). O2 played a crucial rule in the Cu(I)-catalyzed reaction; only a trace amount of product of 2a or 3a was obtained under a nitrogen atmosphere. DMAP and NMI might act as ligands rather than bases because K2CO3, Cs2CO3, or DBU could not initiate the reaction. The chemoselective conversion to 2a and 3a was controlled by the copper salts and ligands (Table 1, entries 5 and 12). This was attractive as a highly selective synthesis derived from the same reactants was a formidable challenge in organic

synthesis.8 To investigate the generality of these two kinds of selective transformations, the optimized conditions (Table 1, entries 5 and 12) were applied for various 2-ethoxycarbonylacetamides, respectively (Tables 2 and 3). Under the CuI/DMAP conditions, both N-aryl- and N-alkysubstituted 2-ethoxycarbonylacetamides reacted well with C60 to give the methanofullerenes 2 (Table 2). When R was a phenyl ring with a strong electron-withdrawing group (NO2) or electron-donating group (OMe), the product yields were lower (Table 2, entries 2 and 5). Alkyl group-substituted 2ethoxycarbonylacetamides also gave the desired products. However, sterically bulky alkyl groups led to lower yields. (Table 2, entry 8). Under the CuCl/NMI conditions, the reaction of C60 with all of the substrates proceeded well to furnish the dihydrofuran-fused fullerenes 3 (Table 3). In the case of Nalkyl-2-ethoxycarbonylaceteamides, the secondary isopropyl and tertiary butyl products were obtained in higher yields than that of the primary n-butyl analogue (Table 3, entries 6− 9). The methanofullerenes 2 contained a highly strained cyclopropane skeleton, which was liable to undergo ringopening under basic or acidic conditions.9 Taking into account the existence of a nucleophilic nitrogen atom in 2, a route to fulleropyrrolidinones 4 through isomerization was proposed (Table 4). 10 Unfortunately, under Bu 4 NI, Zn(OTf) 2 , CF3SO3H, or t-BuOK conditions, no reaction occurred and 2a was totally recovered. Next, we turned our attention to the dihydrofuran-fused fullerenes 3. To our delight, when 3a was treated with 5 equiv of BF3·Et2O at 80 °C for 10 h, it was transformed to the desired fulleropyrrolidinone 4a in 45% yield (Table 4, entry 2). However, no improvement in the yield was observed by further prolonging the reaction time. Increasing the reaction temperature to 120 °C could complete the transformation within 3.5 15269

DOI: 10.1021/acs.joc.8b02547 J. Org. Chem. 2018, 83, 15268−15276

Article

The Journal of Organic Chemistry Table 2. CuI/DMAP System-Catalyzed Reaction of C60 with 2-Ethoxycarbonylaceteamides

Table 3. CuCl/NMI System-Catalyzed Reaction of C60 with 2-Ethoxycarbonylaceteamides

a

Isolated yield; the values in parentheses are based on consumed C60.

h and provided a single product as determined by TLC. However, 1H NMR analysis revealed that it was a mixture of 4a and a de-estered product 5a with a molar ratio of 8:1 (Table 4, entry 1). Although the chemoselectivity was not perfect here, the reaction could be completed in a short time with excellent yields. Other acidic catalysts such as Cu(OTf)2, Zn(OTf)2, Sc(OTf) 3, CF3 SO 3H, and TsOH were also examined (Supporting Information). The use of 1 equiv of CF3SO3H or TsOH resulted in a full decomposition of 3a to C60. Cu(OTf)2 and Zn(OTf)2 showed a low catalytic activity and gave a low yield of 4a with a considerable decomposition to C60. Sc(OTf)3 gave a moderate yield of 4a (49%) with many leftover of 3a even prolonging the reaction time to 12 h. Reducing the amount of BF3·Et2O to 2 equiv led to the incomplete conversion of 3a. The generality of this transformation was examined by subjecting other dihydrofuranfused fullerenes 3 to this condition (Table 4). When R was an aryl group, a striking electronic effect of the substituents was shown. The chemoselectivity exhibited a preference trend toward an increased ratio of 4/5 (1:6−8:1−66:1−100:0) as the increased electron-withdrawing ability of the substituent (OMe−Me−H−Cl) (Table 4, entries 1, 3, 5, and 6). However, a much stronger electron-withdrawing group (NO2) led to no product formation probably due to the weakened nucleophilicity of the nitrogen atom (Table 4, entry 7). When R was an

a

Isolated yield; the values in parentheses are based on consumed C60.

alkyl group, sterically hindered tertiary butyl was not tolerated in this reaction and no conversion was observed (Table 4, entry 11). For benzyl and isopropyl groups, selective conversion to 4f and 4i was achieved (Table 4, entries 8 and 12). In contrast to the benzyl group, n-butyl-substituted 3g furnished the isomerized product 4g and de-estered product 5g with a ratio of 2:1, although they are both the primary alkyl groups (Table 4, entry 9). Interestingly, the reaction temperature showed a significant influence on the distribution of two products. As for 3a, 3b, and 3g, when the temperature was decreased from 120 to 80 °C, the formation of de-estered products 5 could be completely inhibited and selective transformation to 4a, 4b, and 4g was achieved. However, the yields were not satisfactory even with a longer reaction time due to the low conversion of starting materials (Table 4, entries 2, 4, and 10). In order to confirm whether the de-estered products 5 were generated from 4, 4b was treated with BF3·Et2O under the standard reaction conditions (Scheme 2). Most of the 4b was recovered, and only a trace amount of the de-estered product 5b was formed, which indicated that products 4 and 5 were formed simultaneously through different reaction pathways. 15270

DOI: 10.1021/acs.joc.8b02547 J. Org. Chem. 2018, 83, 15268−15276

Article

The Journal of Organic Chemistry Table 4. BF3·Et2O-Mediated Isomerization of 3 to Fulleropyrrolidinones 4 and 5

entry

substrate

t (h)

[4/5]a

yield (%)b

1 2c 3 4c 5 6 7 8 9 10c 11 12

3a (R = 4-MeC6H4) 3a (R = 4-MeC6H4) 3b (R = 4-MeOC6H4) 3b (R = 4-MeOC6H4) 3c (R = Ph) 3d (R = 4-ClC6H4) 3e (R = 4-NO2C6H4) 3f (R = Bn) 3g (R = n-Bu) 3g (R = n-Bu) 3h (R = t-Bu) 3i (R = i-Pr)

3.5 10 3 10 3.5 3 7 3.5 3 13 7 3

8:1 100:0 1:6 100:0 66:1 100:0

90 45 87 50 93 95 0 96 63/31d 54 0 96

100:0 2:1 100:0

Based on previously reported transition-metal-promoted reaction of C60 with ketones or malonate esters,11 a possible mechanism was proposed in Scheme 3. The reaction of Cu(I) with O2 in the presence of DMAP or NMI may generate a Cu(II) complex.12 The C-centered radical 6 generated from the oxidation of 2-ethoxycarbonylacetamide 1 by Cu(II)13 adds to C60 to form fullerenyl radical 7. The same oxidative process occurs to form biradicals 8 followed by coupling to furnish 2 (path A). Cyclization of 7 can also generate a radical 10. Its further oxidation with Cu(II) along with the release of a proton provides 12, which equals to 3 (path B). A mechanism via fullerene cationic species is also possible (path C). Oxidation of 7 by Cu(II) affords fullerenyl cation 9.14 The intramolecular nucleophilic attack by the C/O atom will provide 2 and cation 11, respectively. Under BF3·Et2O conditions, the C−O bond cleavage of 3 gives the zwitterion 13, which undergoes intramolecular nucleophilic attack by the nitrogen atom to generate 14. Subsequent extrusion of BF3 from 14 affords 15, which equilibrates to 4. As for the formation of de-estered product 5, it was probably formed through a similar Krapcho reaction pathway.15 Certainly, the de-ester reaction occurred before the cyclization of 13 to 14 because 4 could not be transformed to 5 directly under the standard conditions.

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Scheme 2. Control Experiment

CONCLUSION In summary, we have developed a highly tunable coppercatalyzed reaction of C60 with 2-ethoxycarbonylacetamides for the selective preparation of methanofullerenes and dihydrofuran-fused fullerenes under the CuI/DMAP system and CuCl/ NMI system, respectively. In addition, the generated dihydrofuran-fused fullerenes provided a good opportunity for the preparation of unprecedented fulleropyrrolidinones upon BF3·Et2O treatment.

The identification of novel fulleropyrrolidinone 4 and 5 were fully characterized by their HRMS, 1H NMR, 13C NMR, and UV−vis spectroscopy (Supporting Information). Take 4a as an example, MALDI-TOF MS of 4a gave the correct M+ peak at 939.0879. The 1H NMR spectrum exhibited all of the signals for the aromatic, methyl, ethyl, and methyne (5.53 ppm, singlet) group. In the 13C NMR spectrum, there were two peaks at 168.34 and 167.48 ppm for the CO2Et and CON group, four peaks at 62.55, 58.50, 21.47, and 14.33 ppm for the OEt, Me, and CH units, 57 peaks in the range 130.16−154.43 ppm with some overlaps due to the sp2 carbons of the C60 skeleton and aryl ring, and two peaks at about 64.47 and 82.22 ppm for the two sp3 carbons of the C60. The nitrogen atom bonding directly to the sp3-C of C60 cage resulted in the downfield shift. The spectral data was fully consistent with its molecular structure. The de-estered products 5b and 5g with Cs symmetry could also be confirmed from their 13C NMR spectra, in which there were no more than 30 peaks in the region of sp2-C except the aryl carbon, as well as only one singlet for the CH2 group in their 1H NMR spectra.

General Information. 1H and 13C NMR (broadband decoupling) spectra were recorded on 400 and 500 MHz (100 and 125 MHz for 13 C NMR) spectrometers at ambient temperature, using TMS as an internal standard. Flash column chromatography was performed over silica gel (200−300 mesh). The MALDI-TOF MS were measured in positive-ion mode using DCTB E-(2-[3-(4-tertbutylphenyl)-2-methyl2-propenylidene]malononitrile) as the matrix. UV−vis spectra were conducted on a Shimadzu UV-2401 spectrometer with CHCl3 as the solvent. The 2-ethoxycarbonylacetamides were prepared through the reaction of amines with ethyl chloroformyl acetate according to the reported procedure.16 General Procedure for the Reaction of C60 with 2Ethoxycarbonylacetamides (1a−h) Catalyzed by the CuI/ DMAP System. To a big tube (Φ25 × 180 mm) were sequentially added C60 (36.0 mg, 0.05 mmol), 2-ethoxycarbonylacetamides (1a−h, 0.10 mmol), CuI (1.9 mg, 0.01 mmol), 10 mL of chlorobenzene, and 100 μL of chlorobenzen solution of DMAP (24.4 mg in 10 mL of PhCl, 0.02 mol/L). The mixture was vigorously stirred at 120 °C until no changes as monitored by TLC. The solvent was evaporated in vacuo, and the residue was purified by column chromatography on silica gel eluted with CS2−toluene (from 100:0 to 0:100, gradient elution) to give the corresponding methanofullerenes 2a−h. Compound 2a (brown solid, 16.1 mg, 34% yield, mp > 300 °C): 1 H NMR (500 MHz, CDCl3−CS2) δ 8.45 (s, 1H), 7.55 (d, J = 8.4 Hz, 2H), 7.18 (d, J = 8.2 Hz, 2H), 4.57 (q, J = 7.1 Hz, 2H), 2.36 (s, 3H), 1.49 (t, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 164.49, 158.10, 145.47, 145.43, 145.22, 145.19, 145.16, 145.14, 145.08, 144.78, 144.71, 144.69, 144.62, 144.59, 144.58, 144.55, 143.80, 143.77, 143.06, 143.04, 142.99, 142.98, 142.88, 142.21,

100:0

a

Molar ratio determined by 1H NMR analysis. bIsolated yield of the single product or mixtures of 4 and 5. cCarried out at 80 °C. dYield of 4g/5g.

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15271

EXPERIMENTAL SECTION

DOI: 10.1021/acs.joc.8b02547 J. Org. Chem. 2018, 83, 15268−15276

Article

The Journal of Organic Chemistry Scheme 3. Possible Reaction Mechanism

(MALDI-TOFMS) m/z [M]+ calcd for C71H11NO3 925.0739, found 925.0731. Compound 2d (brown solid, 10.1 mg, 21% yield, mp > 300 °C): 1 H NMR (500 MHz, CDCl3−CS2) δ 8.61 (s, 1H), 7.64 (d, J = 8.8 Hz, 2H), 7.35 (d, J = 8.8 Hz, 2H), 4.58 (q, J = 7.1 Hz, 2H), 1.49 (t, J = 7.2 Hz, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 164.55, 158.43, 145.38, 145.30, 145.25, 145.23, 145.16, 145.06, 144.87, 144.78, 144.70, 144.68, 144.64, 144.60, 143.85, 143.83, 143.14, 143.09, 143.07, 142.96, 142.26, 142.21, 142.11, 141.99, 141.09, 141.08, 138.53, 138.23, 135.84, 130.68, 129.36, 121.30, 72.52 (sp3-C of C60), 64.10, 56.12, 14.44; UV−vis (CHCl3) λmax/nm 259, 327, 427, 488, 689; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C71H10ClNO3 959.0349, found 959.0341. Compound 2e (brown solid, 8.2 mg, 17% yield, mp > 300 °C): 1H NMR (500 MHz, CDCl3−DMSO-d6−CS2) δ 11.59 (s, 1H), 8.17 (d, J = 9.0 Hz, 2H), 7.99 (d, J = 9.1 Hz, 2H), 4.50 (q, J = 7.0 Hz, 2H), 1.45 (t, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3−DMSO-d6− CS2) δ 163.00, 159.50, 146.22, 144.87, 144.56, 144.49, 144.47, 144.41, 144.39, 144.18, 144.07, 144.01, 143.98, 143.84, 143.77, 143.73, 143.16, 143.10, 142.75, 142.37, 142.29, 142.26, 142.23, 142.18, 141.53, 141.46, 141.39, 141.02, 140.11, 140.05, 139.37, 136.84, 124.01, 118.96, 71.98 (sp3-C of C60), 62.51, 55.22, 13.78; UV−vis (CHCl3) λmax/nm 259, 327, 426, 489, 689; HRMS (MALDITOFMS) m/z [M]+ calcd for C71H10N2O5 970.0590, found 970.0581. Compound 2f (brown solid, 10.8 mg, 23% yield, mp > 300 °C): 1H NMR (500 MHz, CDCl3−CS2) δ 7.36 (d, J = 6.8 Hz, 2H), 7.32 (t, J = 7.3 Hz, 2H), 7.27 (t, J = 7.1 Hz, 1H), 6.96 (t, J = 5.7 Hz, 1H), 4.69

142.16, 142.10, 141.97, 141.01, 140.99, 138.50, 138.13, 134.90, 134.74, 129.77, 120.06, 72.65 (sp3-C of C60), 63.95, 56.39, 21.10, 14.43; UV−vis (CHCl3) λmax/nm 259, 326, 427, 487, 688; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C72H13NO3 939.0895, found 939.0893. Compound 2b (brown solid, 9.1 mg, 19% yield, mp > 300 °C): 1H NMR (500 MHz, CDCl3−CS2) δ 8.38 (s, 1H), 7.58 (d, J = 8.8 Hz, 2H), 6.91 (d, J = 8.8 Hz, 2H), 4.58 (q, J = 7.1 Hz, 2H), 3.81 (s, 3H), 1.50 (t, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 164.66, 158.42, 157.27, 145.59, 145.32, 145.29, 145.26, 145.25, 145.19, 144.89, 144.81, 144.78, 144.73, 144.68, 144.64, 143.89, 143.87, 143.16, 143.12, 143.10, 143.08, 142.99, 142.31, 142.26, 142.22, 142.08, 141.10, 141.08, 138.58, 138.28, 130.35, 121.99, 114.50, 72.82 (sp3-C of C60), 64.01, 56.43, 55.44, 14.46; UV−vis (CHCl3) λmax/nm 259, 326, 427, 488, 689; HRMS (MALDITOFMS) m/z [M]+ calcd for C72H13NO4 955.0845, found 955.0836. Compound 2c (brown solid, 16.2 mg, 35% yield, mp > 300 °C): 1 H NMR (500 MHz, CDCl3−DMSO-d6−CS2) δ 11.01 (s, 1H), 7.74 (d, J = 7.9 Hz, 2H), 7.32 (t, J = 7.8 Hz, 2H), 7.11 (t, J = 7.4 Hz, 1H), 4.52 (q, J = 7.1 Hz, 2H), 1.47 (t, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3−DMSO-d6−CS2) δ 163.46, 158.94, 146.65, 145.00, 144.93, 144.69, 144.41, 144.36, 144.33, 144.04, 144.00, 143.96, 143.79, 143.68, 143.62, 143.13, 143.09, 142.29, 142.23, 142.18, 142.14, 141.51, 141.46, 141.44, 141.09, 139.99, 139.10, 138.13, 136.89, 128.13, 123.72, 119.62, 72.44 (sp3-C of C60), 62.38, 55.75, 13.74; UV−vis (CHCl3) λmax/nm 260, 327, 427, 487, 689; HRMS 15272

DOI: 10.1021/acs.joc.8b02547 J. Org. Chem. 2018, 83, 15268−15276

Article

The Journal of Organic Chemistry

(m, 2H), 7.41 (d, J = 8.4 Hz, 2H), 4.33 (q, J = 6.9 Hz, 2H), 1.27 (t, J = 6.9 Hz, 3H); 13C NMR (125 MHz, DMSO-d6−CS2) δ 165.36, 162.48, 148.98, 147.09, 146.32, 145.65, 145.48, 145.34, 145.03, 144.97, 144.53, 144.23, 144.18, 143.89, 143.60, 143.56, 143.20, 143.08, 142.03, 141.94, 141.77, 141.75, 141.67, 141.32, 141.29, 140.61, 140.21, 138.67, 138.42, 137.19, 135.13, 133.79, 128.65, 128.52, 120.60, 102.27 (sp3-C of C60), 79.75 68.01 (sp3-C of C60), 59.10, 13.65; UV−vis (CHCl3) λmax/nm 256, 314, 457, 687; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C71H10ClNO3 959.0349, found 959.0348. Compound 3e (brown solid, 23.2 mg, 24% yield, mp > 300 °C): 1 H NMR (500 MHz, CDCl3−CS2) δ 10.61 (s, br, 1H), 8.31 (d, J = 9.2 Hz, 2H), 7.76 (d, J = 9.2 Hz, 2H), 4.34 (q, J = 7.1 Hz, 2H), 1.22 (br, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 149.29, 148.18, 147.42, 146.57, 146.54, 146.45, 146.14, 146.06, 145.52, 145.34, 145.27, 144.99, 144.58, 144.43, 144.22, 143.51, 143.27, 143.20, 142.84, 142.77, 142.41, 142.35, 142.33, 141.64, 141.16, 139.81, 139.50, 138.22, 134.91, 125.53, 119.06, 104.03 (sp3-C of C60), 83.24, 68.72 (sp3-C of C60), 60.62, 14.27; UV−vis (CHCl3) λmax/nm 256, 320, 685; HRMS (MALDI-TOFMS) m/z M+ calcd for C71H10N2O5 970.0590, found 970.0578. Compound 3f (brown solid, 17.8 mg, 19% yield, mp > 300 °C): 1H NMR (500 MHz, CDCl3−CS2) δ 8.15 (s, br, 1H), 7.52 (d, J = 7.4 Hz, 2H), 7.43 (t, J = 7.6 Hz, 2H), 7.34 (t, J = 7.4 Hz, 1H), 4.91 (d, J = 6.2 Hz, 2H), 4.22 (q, J = 7.0 Hz, 2H), 1.14 (br, 3H); 13C NMR (125 MHz, DMSO-d6−CS2) δ 150.08, 147.21, 146.43, 145.99, 145.59, 145.37, 145.11, 145.07, 145.05, 144.77, 144.27, 144.01, 143.98, 143.86, 143.81, 143.34, 142.19, 141.88, 141.83, 141.76, 141.47, 141.42, 141.39, 140.76, 140.42, 138.71, 138.43, 137.52, 137.33, 133.75, 128.05, 126.85, 101.26 (sp3-C of C60), 76.44, 69.26 (sp3-C of C60), 58.43, 45.38, 13.92; UV−vis (CHCl3) λmax/nm 255, 317, 457, 687; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C72H13NO3 939.0895, found 939.0885. Compound 3g (brown solid, 14.4 mg, 16% yield, mp > 300 °C): 1 H NMR (500 MHz, CDCl3−CS2) δ 7.86 (s, 1H), 4.22 (q, J = 6.9 Hz, 2H), 3.73 (q, J = 6.9 Hz, 2H), 1.85 (quint, J = 7.3 Hz, 2H), 1.62 (sext, J = 7.4 Hz, 2H), 1.14 (t, J = 6.7 Hz, 3H), 1.09 (t, J = 7.4 Hz, 3H); 13C NMR (100 MHz, DMSO-d6−CS2) δ 165.63, 165.20, 150.17, 147.19, 146.39, 145.94, 145.57, 145.33, 145.03, 144.74, 144.23, 144.09, 143.95, 143.84, 143.79, 143.32, 142.19, 141.86, 141.80, 141.73, 141.44, 141.40, 141.36, 140.74, 140.39, 138.67, 138.41, 137.30, 133.67, 101.18 (sp3-C of C60), 75.83, 69.09 (sp3-C of C60), 58.35, 41.45, 32.27, 19.85, 13.91, 13.53; UV−vis (CHCl3) λmax/ nm 256, 317, 457, 687; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C69H15NO3 905.1052, found 905.1047. Compound 3h (brown solid, 23.6 mg, 26% yield, mp > 300 °C): 1 H NMR (500 MHz, DMSO-d6−CS2) δ 8.12 (s, 1H), 4.13 (q, J = 6.9 Hz, 2H), 1.69 (s, 9H), 1.10 (br, 3H); 13C NMR (125 MHz, DMSOd6−CS2) δ 165.63, 165.47, 149.95, 147.20, 146.40, 145.97, 145.60, 145.39, 145.08, 145.07, 145.04, 144.76, 144.27, 144.25, 143.96, 143.93, 143.84, 143.79, 143.32, 142.18, 141.88, 141.83, 141.75, 141.46, 141.42, 141.37, 140.74, 140.37, 138.72, 138.43, 137.36, 133.66, 101.62 (sp3-C of C60), 76.68, 68.32 (sp3-C of C60), 58.49, 51.87, 29.43, 13.89; UV−vis (CHCl3) λmax/nm 256, 317, 457, 688; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C69H15NO3 905.1052, found 905.1040. Compound 3i (brown solid, 27.0 mg, 30% yield, mp > 300 °C): 1H NMR (400 MHz, CDCl3−CS2) δ 7.74 (s, 1H), 4.30−4.43 (m, 1H), 4.22 (q, J = 6.9 Hz, 2H), 1.53 (d, J = 6.4 Hz, 6H), 1.14 (br, 3H); 13C NMR (125 MHz, DMSO-d6−CS2) δ 165.14, 150.17, 147.27, 146.48, 146.03, 145.66, 145.43, 145.13, 144.82, 144.31, 144.11, 144.03, 143.91, 143.87, 143.39, 142.26, 141.95, 141.89, 141.82, 141.53, 141.47, 140.82, 140.46, 138.76, 138.51, 137.41, 133.76, 101.38 (sp3-C of C60), 75.94, 69.07 (sp3-C of C60), 58.48, 44.27, 23.03, 13.97; UV− vis (CHCl3) λmax/nm 256, 317, 458, 687; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C68H13NO3 891.0895, found 891.0888. General Procedure for the BF3·Et2O-Mediated Transformation of 3 to Fulleropyrrolidinones 4 and 5. A mixture of the dihydrofuran-fused fullerenes (3a−i, 0.02 mmol) and BF3·Et2O (13 μL, 0.10 mmol) in 5 mL of PhCl was stirred at 120 °C under a

(d, J = 5.9 Hz, 2H), 4.50 (q, J = 7.1 Hz, 2H), 1.43 (t, J = 7.1 Hz, 3H); 13 C NMR (125 MHz, CDCl3−CS2) δ 164.08, 160.56, 145.60, 145.54, 145.19, 145.18, 145.16, 145.12, 145.05, 144.74, 144.67, 144.64, 144.60, 144.59, 144.52, 144.50, 143.77, 143.76, 143.06, 143.04, 142.97, 142.95, 142.89, 142.18, 142.15, 141.99, 141.93, 140.94, 140.93, 138.40, 138.31, 137.34, 128.86, 128.00, 127.96, 72.65 (sp3-C of C60), 63.58, 55.61, 44.82, 14.36; UV−vis (CHCl3) λmax/nm 259, 327, 427, 489, 689; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C72H13NO3 939.0895, found 939.0892. Compound 2g (brown solid, 10.7 mg, 24% yield, mp > 300 °C): 1 H NMR (500 MHz, CDCl3−CS2) δ 6.66 (s, 1H), 4.53 (q, J = 7.1 Hz, 2H), 3.53 (q, J = 6.6 Hz, 2H), 1.67 (quint, J = 7.3 Hz, 2H), 1.43− 1.51 (m, 5H), 0.99 (t, J = 7.4 Hz, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 164.45, 160.56, 145.79, 145.73, 145.23, 145.17, 145.13, 144.78, 144.72, 144.65, 144.63, 144.55, 144.53, 143.82, 143.80, 143.10, 143.09, 143.02, 143.00, 142.92, 142.23, 142.19, 142.08, 142.02, 140.99, 138.43, 138.16, 72.87 (sp3-C of C60), 63.61, 56.02, 40.62, 31.79, 20.41, 14.41, 13.93; UV−vis (CHCl3) λmax/nm 259, 327, 427, 490, 689; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C69H15NO3 905.1052, found 905.1049. General Procedure for the Reaction of C60 with 2Ethoxycarbonylacetamides (1a−i) Catalyzed by the CuCl/ NMI System. To a big tube (Φ25 × 180 mm) were sequentially added C60 (72.0 mg, 0.10 mmol), 2-ethoxycarbonylacetamides (1a−i, 0.20 mmol), CuCl (1.9 mg, 0.02 mmol), 20 mL of chlorobenzene, and 100 μL of chlorobenzen solution of N-methylimidazole (32.8 mg in 10 mL of PhCl, 0.04 mol/L). The mixture was vigorously stirred at 120 °C until no changes as monitored by TLC. The solvent was evaporated in vacuo, and the residue was purified by column chromatography on silica gel eluted with CS2−toluene (from 100:0 to 0:100, gradient elution) to give the corresponding dihydrofuran-fused fullerene derivatives 3a−i. Compound 3a (brown solid, 27.2 mg, 29% yield, mp > 300 °C): 1 H NMR (500 MHz, CDCl3−CS2) δ 10.01 (s, 1H), 7.48 (d, J = 8.4 Hz, 2H), 7.21 (d, J = 8.3 Hz, 2H), 4.30 (q, J = 7.0 Hz, 2H), 2.38 (s, 3H), 1.19 (br, 3H); 13C NMR (125 MHz, C6D6−CS2) δ 166.90, 164.26, 150.64, 148.41, 147.63, 147.05, 146.80, 146.63, 146.34, 146.28, 146.27, 145.90, 145.53, 145.49, 145.20, 144.97, 144.95, 144.71, 144.65, 144.53, 143.33, 143.09, 143.06, 142.98, 142.65, 142.61, 141.95, 141.59, 139.96, 139.73, 138.53, 135.29, 135.10, 133.79, 130.36, 120.85, 103.42 (sp3-C of C60), 80.19, 69.43 (sp3-C of C60), 60.19, 21.49, 14.97; UV−vis (CHCl3) λmax/nm 256, 313, 459, 687; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C72H13NO3 939.0895, found 939.0894. Compound 3b (brown solid, 29.6 mg, 31% yield, mp > 300 °C): 1 H NMR (500 MHz, DMSO-d6−CS2) δ 9.94 (s, 1H), 7.54 (d, J = 8.9 Hz, 2H), 6.96 (d, J = 8.9 Hz, 2H), 4.31 (q, J = 7.1 Hz, 2H), 3.88 (s, 3H), 1.26 (t, J = 7.0 Hz, 3H); 13C NMR (125 MHz, DMSO-d6−CS2) δ 165.35, 162.96, 155.70, 149.52, 147.16, 146.39, 145.85, 145.55, 145.37, 145.08, 145.04, 145.02, 144.67, 144.36, 144.27, 144.24, 143.95, 143.75, 143.72, 143.57, 143.47, 143.29, 143.04, 142.10, 141.84, 141.80, 141.72, 141.41, 141.40, 141.36, 140.71, 140.35, 138.70, 138.46, 137.30, 133.83, 129.43, 121.74, 113.78, 101.90 (sp3-C of C60), 78.36, 68.36 (sp3-C of C60), 58.92, 54.30, 13.82; UV−vis (CHCl3) λmax/nm 256, 313, 459, 687; HRMS (MALDI-TOFMS) m/ z [M]+ calcd for C72H13NO4 955.0845, found 955.0833. Compound 3c (brown solid, 25 mg, 27% yield, mp > 300 °C): 1H NMR (400 MHz, CDCl3−CS2) δ 10.10 (s, 1H), 7.60 (d, J = 7.8 Hz, 2H), 7.41 (t, J = 8.0 Hz, 2H), 7.16 (t, J = 7.4 Hz, 1H), 4.31 (q, J = 6.8 Hz, 2H), 1.19 (br, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 167.27, 164.11, 150.15, 148.15, 147.37, 146.73, 146.52, 146.34, 146.06, 145.99, 145.61, 145.26, 145.21, 144.93, 144.66, 144.64, 144.28, 144.23, 143.96, 143.04, 142.96, 142.78, 142.76, 142.68, 142.42, 142.34, 142.30, 141.64, 141.24, 139.68, 139.40, 138.26, 137.43, 134.85, 129.47, 124.24, 120.41, 103.33 (sp3-C of C60), 80.45, 69.06 (sp3-C of C60), 60.02, 14.37; UV−vis (CHCl3) λmax/nm 256, 312, 459, 687; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C71H11NO3 925.0739, found 925.0735. Compound 3d (brown solid, 25.5 mg, 27% yield, mp > 300 °C): 1 H NMR (500 MHz, DMSO-d6−CS2) δ 10.22 (s, 1H), 7.56−7.67 15273

DOI: 10.1021/acs.joc.8b02547 J. Org. Chem. 2018, 83, 15268−15276

Article

The Journal of Organic Chemistry nitrogen atmosphere until the full conversion of 3. The solvent was evaporated in vacuo, and the residue was purified by column chromatography on silica gel eluted with CS2−toluene (from 100:0 to 0:100, gradient elution) to give the corresponding products 4 and/or 5. (Compounds 3e and 3h have no reaction. Compounds 4b/5b and 4g/5g could be separated by column chromatography; others products were obtained as single products or an inseparable mixture of 4 and 5.) Compound 4a (brown solid, a mixture of 4a/5a = 8:1, 16.7 mg, 90% yield, mp > 300 °C): 1H NMR (500 MHz, CDCl3−CS2) δ 7.61 (d, J = 8.1 Hz, 2H), 7.35 (d, J = 8.1 Hz, 2H), 5.53 (s, 1H), 4.38−4.49 (m, 2H), 2.41 (s, 3H), 1.36 (t, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 168.34, 167.48, 154.43, 150.98, 148.10, 147.78, 147.16, 146.68, 146.59, 146.53, 146.44, 146.37, 146.27, 146.25, 146.24, 146.21, 145.66, 145.62, 145.60, 145.39, 145.38, 145.28, 145.12, 145.03, 144.84, 144.79, 144.71, 144.46, 144.43, 144.41, 143.11, 143.10, 142.94, 142.82, 142.76, 142.72, 142.38, 142.35, 142.13, 142.07, 142.02, 142.01, 141.99, 141.92, 141.81, 141.79, 141.68, 141.65, 140.38, 139.71, 139.53, 139.44, 137.40, 137.11, 136.13, 134.91, 133.22, 130.41, 130.16, 84.22 (sp3-C of C60), 64.47 (sp3-C of C60), 62.55, 58.50, 21.47, 14.33; UV−vis (CHCl3) λmax/nm 256, 317, 430, 690; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C72H13NO3 939.0895, found 939.0879. Compound 5b (brown solid, a mixture of 4b/5b = 1:6, 15.5 mg, 87% yield, mp > 300 °C): 1H NMR (500 MHz, CDCl3−CS2) δ 7.56 (d, J = 8.8 Hz, 2H), 7.00 (d, J = 9.0 Hz, 2H), 4.58 (s, 2H), 3.82 (s, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 171.93, 160.03, 155.21, 148.08, 147.69, 147.00, 146.54, 146.41, 146.36, 146.25, 146.23, 145.68, 145.49, 145.39, 145.30, 145.17, 144.81, 144.63, 144.40, 143.12, 142.88, 142.70, 142.31, 142.22, 142.07, 142.03, 141.86, 141.79, 140.44, 139.45, 136.75, 134.86, 131.46, 128.71, 114.99, 84.95 (sp3-C of C60), 61.42 (sp3-C of C60), 55.30, 42.84; UV−vis (CHCl3) λmax/nm 256, 316, 430, 692; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C69H9NO2 883.0633, found 883.0617. Compound 4c (brown solid, a mixture of 4c/5c = 88:1, 17.2 mg, 93% yield, mp > 300 °C): 1H NMR (500 MHz, CDCl3−CS2) δ 7.69 (d, J = 7.7 Hz, 2H), 7.52 (t, J = 7.6 Hz, 2H), 7.46 (t, J = 7.5 Hz, 1H), 5.46 (s, 1H), 4.34−4.45 (m, 2H), 1.36 (t, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 168.21, 167.38, 154.37, 150.94, 148.09, 147.76, 147.05, 146.57, 146.52, 146.42, 146.36, 146.27, 146.24, 146.23, 146.21, 145.65, 145.59, 145.58, 145.38, 145.37, 145.35, 145.26, 144.99, 144.78, 144.70, 144.44, 144.41, 144.37, 143.10, 143.09, 142.93, 142.81, 142.75, 142.71, 142.37, 142.34, 142.11, 142.04, 142.01, 141.98, 141.89, 141.79, 141.76, 141.65, 141.62, 140.39, 139.72, 139.42, 137.43, 137.08, 136.16, 135.92, 134.89, 130.43, 129.69, 129.44, 84.12 (sp3-C of C60), 64.53 (sp3-C of C60), 62.55, 58.49, 14.33; UV−vis (CHCl3) λmax/nm 256, 317, 430, 690; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C71H11NO3 925.0739, found 925.0730. Compound 4d (brown solid, 18.2 mg, 95% yield, mp > 300 °C): 1 H NMR (500 MHz, CDCl3−CS2) δ 7.65 (d, J = 8.7 Hz, 2H), 7.50 (d, J = 8.8 Hz, 2H), 5.45 (s, 1H), 4.34−4.45 (m, 2H), 1.35 (t, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 168.33, 167.32, 154.13, 150.68, 148.11, 147.79, 146.60, 146.54, 146.44, 146.39, 146.34, 146.27, 146.25, 146.10, 145.67, 145.60, 145.55, 145.53, 145.41, 145.37, 145.28, 144.90, 144.79, 144.71, 144.49, 144.42, 144.40, 144.29, 143.12, 142.97, 142.85, 142.78, 142.74, 142.38, 142.35, 142.11, 142.04, 142.02, 141.98, 141.97, 141.95, 141.84, 141.70, 141.60, 140.42, 139.75, 139.54, 137.56, 137.00, 136.26, 135.87, 134.81, 134.33, 131.71, 130.02, 83.98 (sp3-C of C60), 64.52 (sp3-C of C60), 62.65, 58.36, 14.33; UV−vis (CHCl3) λmax/nm 256, 317, 430, 688; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C71H10ClNO3 959.0349, found 959.0330. Compound 4f (brown solid, 18.0 mg, 96% yield, mp > 300 °C): 1H NMR (500 MHz, CDCl3−CS2) δ 7.61 (d, J = 7.4 Hz, 2H), 7.33 (t, J = 7.6 Hz, 2H), 7.25 (t, J = 7.3 Hz, 1H), 5.77 (d, J = 8.0 Hz, 1H), 5.47 (s, 1H), 5.33 (d, J = 7.9 Hz, 1H), 4.36−4.50 (m, 2H), 1.36 (t, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 168.24, 167.48, 154.58, 150.60, 148.06, 147.72, 146.54, 146.49, 146.35, 146.29, 146.23, 146.13, 145.55, 145.51, 145.36, 145.27, 145.21, 144.73,

144.65, 144.52, 144.37, 143.09, 142.91, 142.75, 142.30, 142.17, 142.12, 141.98, 141.96, 141.87, 141.77, 141.69, 141.59, 141.50, 140.41, 139.73, 139.33, 139.23, 137.10, 136.44, 134.72, 128.71, 128.30, 127.88, 82.62 (sp3-C of C60), 64.58 (sp3-C of C60), 62.54, 58.25, 46.76, 14.32; UV−vis (CHCl3) λmax/nm 257, 318, 430, 689. HRMS (MALDI-TOFMS) m/z [M]+ calcd for C72H13NO3 939.0895, found 939.0875. Compound 4g (brown solid, 11.4 mg, 63% yield, mp > 300 °C): 1 H NMR (500 MHz, CDCl3−CS2) δ 5.27 (s, 1H), 4.25−4.39 (m, 2H), 4.17 (ddd, J = 14.8, 9.3, 5.9 Hz, 1H), 1.94−2.12 (m, 2H), 1.58 (sext, J = 7.3 Hz, 2H), 1.31 (t, J = 7.1 Hz, 3H), 1.02 (t, J = 7.4 Hz, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 167.77, 167.42, 154.64, 150.98, 148.06, 147.71, 146.77, 146.66, 146.55, 146.45, 146.34, 146.32, 146.22, 145.55, 145.52, 145.49, 145.37, 145.35, 145.25, 145.07, 144.78, 144.71, 144.47, 144.41, 144.39, 144.33, 143.14, 143.11, 142.91, 142.80, 142.78, 142.74, 142.34, 142.32, 142.12, 142.06, 141.97, 141.95, 141.91, 141.90, 141.87, 141.83, 141.70, 141.55, 140.35, 139.70, 139.63, 139.57, 137.51, 137.01, 136.48, 134.69, 82.57 (sp3-C of C60), 64.58 (sp3-C of C60), 62.37, 58.22, 43.31, 31.59, 20.70, 14.28, 14.08; UV−vis (CHCl3) λmax/nm 256, 317, 430, 690; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C69H15NO3 905.1052, found 905.1033. Compound 5g (brown solid, 5.2 mg, 31% yield, mp > 300 °C): 1H NMR (500 MHz, CDCl3−CS2) δ 4.41 (s, 2H), 4.19 (t, J = 7.9 Hz, 2H), 2.02 (quint, J = 7.7 Hz, 2H), 1.54 (sext, J = 7.4 Hz, 2H), 1.02 (t, J = 7.3 Hz, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 171.15, 155.41, 148.10, 147.67, 146.91, 146.55, 146.36, 146.27, 146.25, 145.68, 145.41, 145.32, 144.85, 144.69, 144.39, 143.19, 142.90, 142.76, 142.32, 142.16, 142.12, 142.01, 141.96, 141.88, 140.47, 139.61, 137.04, 134.78, 83.20 (1C, sp3-C of C60), 61.66 (1C, sp3-C of C60), 43.28, 42.62, 31.67, 20.87, 14.07; UV−vis (CHCl3) λmax/nm 256, 316, 430, 692; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C66H11NO 833.0841, found 833.0821. Compound 4i (brown solid, 17.1 mg, 96% yield, mp > 300 °C): 1H NMR (400 MHz, CDCl3−CS2) δ 5.23 (s, 1H), 4.90 (heptet, J = 6.7 Hz, 1H), 4.26−4.42 (m, 2H), 1.88 (d, J = 7.1 Hz, 3H), 1.86 (d, J = 7.3 Hz, 3H), 1.32 (t, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3− CS2) δ 167.90, 167.63, 154.73, 151.53, 148.08, 147.72, 146.94, 146.62, 146.59, 146.49, 146.39, 146.34, 146.22, 146.14, 145.64, 145.61, 145.53, 145.47, 145.37, 145.34, 145.24, 144.98, 144.89, 144.86, 144.80, 144.41, 144.38, 144.28, 143.19, 142.96, 142.84, 142.77, 142.73, 142.42, 142.39, 142.11, 142.04, 141.92, 141.83, 141.73, 141.56, 140.31, 139.68, 139.60, 139.49, 137.97, 136.92, 136.52, 134.73, 82.93 (sp3-C of C60), 64.70 (sp3-C of C60), 62.31, 59.10, 48.95, 20.07, 19.84, 14.28; UV−vis (CHCl3) λmax/nm 256, 316, 430, 691; HRMS (MALDI-TOFMS) m/z [M]+ calcd for C68H13NO3 891.0895, found 891.0890. BF3·Et2O-Promoted Transformation of 3a, 3b, or 3g to Fulleropyrrolidinones 4a, 4b, or 4g at 80 °C. A mixture of the dihydrofuran-fused fullerenes (3a, 3b, or 3g, 0.02 mmol) and BF3· Et2O (13 μL, 0.10 mmol) in 5 mL of PhCl was stirred at 80 °C under a nitrogen atmosphere until no obvious change was detected by TLC. The solvent was evaporated in vacuo, and the residue was purified by column chromatography on silica gel eluted with CS2−toluene (from 100:0 to 0:100, gradient elution) to give the corresponding products 4a (8.5 mg, 45% yield), 4b (9.6 mg, 50% yield), and 4g (9.7 mg, 54% yield). Compound 4b (brown solid, mp > 300 °C): 1H NMR (500 MHz, CDCl3−CS2) δ 7.57 (d, J = 8.7 Hz, 2H), 7.00 (d, J = 9.0 Hz, 2H), 5.43 (s, 1H), 4.33−4.44 (m, 2H), 3.82 (s, 3H), 1.35 (t, J = 7.1 Hz, 3H); 13C NMR (125 MHz, CDCl3−CS2) δ 168.75, 167.70, 160.24, 154.47, 151.00, 148.18, 147.86, 147.20, 146.73, 146.65, 146.60, 146.51, 146.44, 146.33, 145.72, 145.66, 145.46, 145.35, 145.18, 145.09, 144.89, 144.85, 144.78, 144.50, 144.47, 143.17, 143.00, 142.89, 142.82, 142.79, 142.45, 142.41, 142.19, 142.13, 142.08, 142.07, 142.05, 141.99, 141.89, 141.73, 140.44, 139.77, 139.54, 137.46, 137.16, 136.19, 134.97, 131.55, 128.39, 115.05, 84.48 (sp3-C of C60), 64.43 (sp3-C of C60), 62.64, 58.58, 55.42, 14.35; UV−vis (CHCl3) λmax/nm 256, 316, 430, 690; HRMS (MALDI-TOFMS) m/ z [M]+ calcd for C72H13NO4 955.0845, found 955.0831. 15274

DOI: 10.1021/acs.joc.8b02547 J. Org. Chem. 2018, 83, 15268−15276

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The Journal of Organic Chemistry

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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.8b02547. Screening of the conditions for the transformation of 3a to 4a/5a, UV−vis spectra of 2b, 3b, 4b, and 5b, and NMR spectra of 2a−h, 3a−i, 4a−g, 4i, 5b, and 5g (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Qiaoqiao Teng: 0000-0002-7343-8092 Chun-Bao Miao: 0000-0003-4666-2619 Hai-Tao Yang: 0000-0001-9803-5452 Author Contributions †

Q.T. and Y.-C.T. contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful for the financial support from the Natural Science Foundation of Jiangsu Province (BK20181462), the Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology (BM2012110), and the Advanced Catalysis and Green Manufacturing Collaborative Innovation Center.

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REFERENCES

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DOI: 10.1021/acs.joc.8b02547 J. Org. Chem. 2018, 83, 15268−15276

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DOI: 10.1021/acs.joc.8b02547 J. Org. Chem. 2018, 83, 15268−15276