Solvent-free synthesis of N-arylfulleropyrrolidine derivatives without using phase-transfer catalyst under microwave irradiation

Article abstract of DOI:10.1080/00397910903007061

Several N-arylfulleropyrrolidine derivatives were synthesized via the direct solvent-free reactions of N-unsubstituted fulleropyrrolidines and nitrochlorobenzenes under microwave irradiation in the absence of phase-transfer catalysts. Their structures wer

Full text of DOI:10.1080/00397910903007061

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Solvent-Free Synthesis of N-
Arylfulleropyrrolidine Derivatives
Without Using Phase-Transfer Catalyst
Under Microwave Irradiation
Bo Jin a b , Ru-Fang Peng a , Wen-Ning Yang a , Kai Wang a , Bang-Qun
Yuan a & Shi-Jin Chu a
a School of Materials Science and Engineering , Southwest University
of Science and Technology , Mianyang, Sichuan, China
b School of Chemical Engineering and Environment , Beijing Institute
of Technology , Beijing, China
Published online: 03 Feb 2010.
To cite this article: Bo Jin , Ru-Fang Peng , Wen-Ning Yang , Kai Wang , Bang-Qun Yuan & Shi-Jin Chu
(2010) Solvent-Free Synthesis of N-Arylfulleropyrrolidine Derivatives Without Using Phase-Transfer
Catalyst Under Microwave Irradiation, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 40:4, 580-586, DOI: 10.1080/00397910903007061
To link to this article: http://dx.doi.org/10.1080/00397910903007061
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Synthetic Communications1, 40: 580–586, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903007061
SOLVENT-FREE SYNTHESIS OF
N-ARYLFULLEROPYRROLIDINE DERIVATIVES
WITHOUT USING PHASE-TRANSFER CATALYST
UNDER MICROWAVE IRRADIATION
Bo Jin,1,2 Ru-Fang Peng,1 Wen-Ning Yang,1 Kai Wang,1
Bang-Qun Yuan,1 and Shi-Jin Chu1
1School of Materials Science and Engineering, Southwest University
of Science and Technology, Mianyang, Sichuan, China
2School of Chemical Engineering and Environment, Beijing Institute
of Technology, Beijing, China
Several N-arylfulleropyrrolidine derivatives were synthesized via the direct solvent-free
reactions of N-unsubstituted fulleropyrrolidines and nitrochlorobenzenes under microwave
irradiation in the absence of phase-transfer catalysts. Their structures were confirmed
by ultraviolet–visble, Fourier transform–infrared, 1H NMR, and mass spectrometry.
Keywords: N-Arylation; fullerene; fulleropyrrolidine; microwave irradiation; solvent-free
Because of fullerene’s unique geometrical shape and chemical properties, its chemical
derivatization is an important frontier of active research, immediately after the dis-
covery and availability in macroscopic amounts of the most abundant fullerene.[1–7]
Various methods have been developed for functionalizing fullerene and an impress-
ive number of fullerene derivatives have been synthesized.[8–13] Among the wide
variety of organofullerene compounds that have been synthesized and studied, the
family of fulleropyrrolidines has played a prominent role.[14–16] The reaction between
azomethine ylide and fullerene is one of the first reported fullerene reactions and
has been widely studied to prepare fulleropyrrolidine derivatives.[17] To obtain the
N-substituted fulleropyrrolidines, either an N-substituted amino acid was used or
the N-unsubstituted fulleropyrrolidines were modified at the N-H functionality.[18–20]
Because N-nitrophenylfulleropyrrolidine derivatives cannot be easily obtained by
cycloaddition reactions with the corresponding N-substituted amino acid as starting
materials, the N-arylation of N-unsubstituted fulleropyrrolidines is regarded as the
better approach.
Received December 19, 2008.
Address correspondence to Bo Jin and Ru-Fang Peng, School of Materials Science and
Engineering, Southwest University of Science and Technology, Mianyang, Sichuan, 621010, China.
E-mail: jinbo@swust.edu.cn, pengrufang@swust.edu.cn
580

N-ARYLFULLEROPYRROLIDINE DERIVATIVES
581
Microwave irradiation is a clean methodology for introducing energy into reac-
tions, and microwave-assisted organic synthesis can remarkably decrease reaction
time and improve yields of products.[21–23] De la Cruz et al. first reported the N-alky-
lation of N-unsubstituted fulleropyrrolidines to afford N-alkylfulleropyrrolidines
under microwave irradiation by phase-transfer catalysis in the absence of solvent.[19]
Nevertheless, microwave irradiation has not been successfully applied to the
N-arylation of N-unsubstituted fulleropyrrolidines.[24,25] In this article, we report
the N-arylation of N-unsubstituted fulleropyrrolidines with 2,4-dinitrochloroben-
zene and 2,4,6-trinitrochlorobenzene under microwave irradiation without using
solvent or phase-transfer catalysts. To the best of our knowledge, this is the first
example of application of microwave irradiation without using phase-transfer cata-
lyst and solvent for N-arylation of N-unsubstituted fulleropyrrolidines.
RESULTS AND DISCUSSION
Microwave-irradiated, solvent-free, phase-transfer catalysis has been success-
fully applied to N-alkylation of N-unsubstituted fulleropyrrolidines.[19] Our previous
work was to synthesize some N-nitrophenylfulleropyrrolidine derivatives using this
method. Initially, a mixture of 2-(3-nitrophenyl)fulleropyrrolidine 1a (9.2 mg), 2,4,6-
trinitrochlorobenzene (TNCB) (12.6 mg), potassium carbonate (14.2 mg), and tetra-
butylammonium chloride (TBAC) (16.6 mg) was homogenized in an ultrasonic bath
for 10 min and irradiated at 693 W for 5 min to prepare N-(2,4,6-trinitrophenyl)-
2-(3-nitrophenyl)fulleropyrrolidine 3a, but only 10% of the starting material, 20%
of C60, and other unidentified decomposition products were obtained. Various
irradiation powers (297–900 W) and times (0.5–15 min) were studied, and product
3a was not obtained. We thought it might be caused by the phase-transfer catalyst
TBAC, so we tried directly reacting 1a and TNCB without using TBAC and potassium
carbonate. When a binary mixture of 1a (18.0 mg) and TBAC (35.0 mg) was homoge-
nized in an ultrasonic bath for 10 min and heated to 150ꢀC for 8 h, no starting material
was recovered and only some unidentified decomposition products were obtained,
which were not dissolved in organic solvents such as toluene, carbon bisulfide,
dimethylsulfoxide, and chloroform. To our delight, when a binary mixture of 1a
(35.4 mg) and TNCB (224.1 mg) was homogenized in an ultrasonic bath for 10 min
and irradiated at 693 W for 15 min, the aim product 3a was obtained (Scheme 1).
To probe the generality of the reaction for other N-unsubstituted fulleropyrro-
lidines and nitrophenyl chloride, compounds 1b–d and 2a–b were used in the reac-
tion. As we expected, when the binary mixtures of 1b–d and 2a, b were irradiated
at 693 W for 15 min, the corresponding products 3b–e were obtained, as shown in
Scheme 1 and Table 1.
Benzyl halides were also used in the reaction to see if the N-benzyl fulleropyr-
rolidines could be obtained. When the binary mixtures of 1d (0.04 mmol) and 2c, d
(0.90 mmol) were irradiated at 693 W for 15 min and then isolation by flash-column
chromatography on silica gel using a mixture of n-hexane and toluene as eluents, 3f
and 3 g were afforded in 23% and 80% yields respectively (Scheme 1, Table 1).
For the sake of comparison with microwave irradiation, traditional heating has
been chosen to synthesize the products 3a–e with 1a–d and 2a, b as starting materials.
The binary mixtures of 1a–d and 2a, b were heated to 150ꢀC for 8 h, then the

582
B. JIN ET AL.
Scheme 1. Synthesis of 3a–g by the N-arylation of 1a–d with 2a–d under microwave irradiation.
mixtures were cooled to room temperature and purified by flash chromatography
with hexane=toluene (1:2) as eluent to afford products 3a–e. The results of the
reaction are shown in Table 2.
As shown in Tables 1 and 2, N-arylfulleropyrrolidine derivatives 3a–e were
obtained in less reaction time and better yields under microwave irradiation
conditions than with the traditional heating method.
The structures of products 3a–g were characterized by ultraviolet–visible
1
(UV-vis), H NMR, Fourier transform–infrared (FT-IR), and mass (MS) spectral
data. The spectral data of adducts 3f, g are fully consistent with those reported pre-
viously.[19] The UV-vis spectra of products 3a–e have absorption bands around 257,
1
318, and 430 nm. The H NMR spectra of 3a–e in CDCl3 solution show typical sig-
nals of the 2-arylfulleropyrrolidine system, a singlet at d ¼ 6.06–7.33 for H–2, and
two doublets at d ¼ 4.94–5.57 for CH2–5 with JAB ¼ 9.6–10.8 Hz. Products 3a and
1
3c–e exhibit a singlet at d ¼ 8.73–8.78 in their H NMR spectra for N-substituted
2,4,6-trinitrophenyl group in the pyrrole ring. Product 3b shows a doublet at
d ¼ 8.87 (J ¼ 2.4 Hz), a double doublet at d ¼ 8.47 (J ¼ 2.4, 9.0 Hz), and a doublet
at d ¼ 8.00 (J ¼ 9.0 Hz) in their 1H NMR spectra for N-substituted 2,4-dinitrophenyl
group in the pyrrole ring. The IR spectra are very complex, and more than 20
absorption bands were observed. The absorption around 526, 577, 1183, and
Table 1. Reaction results of 1a–d and 2a–d under microwave irradiationa
Entry
Reactants
Products
Yields (%)b
1
2
3
4
5
6
7
0.04 mmol 1a, 0.90 mmol 2b
0.04 mmol 1b, 0.90 mmol 2a
0.04 mmol 1b, 0.90 mmol 2b
0.04 mmol 1c, 0.90 mmol 2b
0.04 mmol 1d, 0.90 mmol 2b
0.04 mmol 1d, 0.90 mmol 2c
0.04 mmol 1d, 0.90 mmol 2d
3a
3b
3c
3d
3e
3f
33
29
18
56
37
23c
80
3g
aIrradiation power and time are 693 W and 15 min, respectively.
bIsolated yields.
c89% based on consumed 2c (74% 2c was recovered).

N-ARYLFULLEROPYRROLIDINE DERIVATIVES
583
Table 2. Reaction results of 1a–d and 2a–b under traditional heatinga
Entry
Reactants
Products
Yields (%)b
1
2
3
4
5
0.04 mmol 1a, 0.90 mmol 2b
0.04 mmol 1b, 0.90 mmol 2a
0.04 mmol 1b, 0.90 mmol 2b
0.04 mmol 1c, 0.90 mmol 2b
0.04 mmol 1d, 0.90 mmol 2b
3a
3b
3c
3d
3e
23
24
17
45
29
aReaction temperature and time are 150ꢀC and 8h respectively.
bIsolated yields.
1460 cmꢁ1 are attributed to the vibration of fullerene core. Bands at 3022–2848 cmꢁ1
show the carbon hydrogen (CꢁH) stretching vibration, and the absorptions around
1500 and 1605 cmꢁ1 are attributed to the stretch vibration of benzene ring. The
absorptions around 1530 and 1343 cmꢁ1 are assigned to asymmetric and symmetric
NO2 stretching modes, respectively. The MS of products 3b and 3c show peaks at
m=z 1050 and 1096, respectively, corresponding to their Mþ and MHþ. Products
3a, 3d, and 3e reveal peaks at m=z 855, 855, and 810, respectively, corresponding
to their molecular ion minus (NO2)3C6H2NCH2 unit.
CONCLUSION
In summary, we have developed a general and efficient microwave-assisted
approach for the synthesis of N-arylfulleropyrrolidine derivatives without solvent
and phase-transfer catalyst. Compared with the traditional heating method,
microwave-assisted, solvent-free reaction has advantages in improved yield and
enhanced reaction rates.
EXPERIMENTAL
General Methods
Reactions were performed in a domestic microwave oven (Midea model
KJ23C-AN). 1H NMR spectra were recorded on a Bruker Ac 300=600 spectrometer
with CS2=CDCl3 as the solvent. Matrix-assisted laser desorption=ionization time-of-
flight (MALDI-TOF) MS were taken on a Bruker BiFlexIII mass spectrometer using
4-hydroxy-a-cyanocinnamic acid as the matrix. The IR spectra were measured on a
Nicolet 380 FT-IR spectrometer (KBr pellet) with a resolution of 4 cmꢁ1, in the
range of 4000–400 cmꢁ1. UV-vis spectra were recorded on Unicon UV-2102 PCS
spectrometer using CHCl3 as the solvent. Chromatographic purifications were car-
ried out with 200- to 300-mesh silica gel. C60 was prepared by arc discharge
method.[26] N-Unsubstituted fulleropyrrolidines 1a–d were afforded by the Prato
reaction.[17] All other commercial reagents are of analytical grade.
Synthesis of N-Arylfulleropyrrolidine Derivatives Under Microwave
Irradiation—General Procedure
A mixture of corresponding N-unsubstituted fulleropyrrolidine (0.04 mmol)
and nitrophenyl chloride (0.90 mmol) was homogenized in an ultrasonic bath for

584
B. JIN ET AL.
10 min and irradiated at 693 W for 15 min. Then the mixture was cooled to room
temperature and washed with carbon disulfide. The solvent was evaporated under
reduced pressure, and the crude product was purified by flash chromatography
[SiO2, hexane=toluene (1:2)] to give the reaction product and the unreacted
N-unsubstituted fulleropyrrolidine.
Synthesis of N-Arylfulleropyrrolidine Derivatives Under Traditional
Heating—General Procedure
A mixture of corresponding N-unsubstituted fulleropyrrolidine (0.04 mmol)
and nitrophenyl chloride (0.90 mmol) was homogenized in an ultrasonic bath for
10 min and heated in an oil bath at 150ꢀC for 8 h. Then the mixture was cooled to
room temperature and washed with carbon disulfide. The solvent was evaporated
under reduced pressure, and the crude product was purified by flash chromatography
[SiO2, hexane=toluene (1:2)] to give the reaction product and the unreacted N-unsub-
stituted fulleropyrrolidine.
Selected Data
N-(2,4,6-Trinitrophenyl)-2-(3-nitrophenyl)fulleropyrrolidine
3a. UV-
1
vis(CHCl3) kmax: 257 (s), 318 (m), 430 (w)nm; H NMR (CS2=CDCl3, 400 MHz)
d: 8.75 (s, 2H), 8.48 (s, 1H), 8.18 (d, J ¼ 8.4 Hz, 1H), 7.95 (d, J ¼ 8.0 Hz, 1H), 7.54
(t, J ¼ 8.0 Hz, 1H), 6.17 (s, 1H), 5.56 (d, J ¼ 10.4 Hz, 1H), 5.42 (d, J ¼ 10.8, 1H)
ppm; IR (KBr) t: 3022, 2920, 2848, 1608, 1530, 1462, 1399, 1351, 1183, 1089,
838, 779, 719, 682, 574, 563, 553, 527 cmꢁ1; MS (MALDI-TOF) m=z: 855
[M-(NO2)3C6H2NCH2]þ, 720 [C60]þ.
N-(2,4-Dinitrophenyl)-2-(2-nitrophenyl)fulleropyrrolidine
3b. UV-
1
vis(CHCl3) kmax: 257 (s), 317 (m), 431 (w)nm; H NMR (CS2=CDCl3, 600 MHz)
d: 8.87 (d, J ¼ 2.4 Hz, 1H), 8.47 (dd, J ¼ 2.4, 9.0 Hz, 1H), 8.27 (d, J ¼ 7.8 Hz, 1H),
8.00 (d, J ¼ 9.0 Hz, 1H), 7.90 (d, J ¼ 8.4 Hz, 1H), 7.64 (t, J ¼ 7.8 Hz, 1H), 7.51 (t,
J ¼ 7.8 Hz, 1H), 7.33 (s, 1H), 5.56 (d, J ¼ 9.6 Hz, 1H), 4.94 (d, J ¼ 9.6, 1H) ppm;
IR (KBr) t: 3019, 2923, 2848, 1604, 1528, 1486, 1463, 1400, 1344, 1187, 1071, 767,
737, 575, 562, 553, 527 cmꢁ1; MS (MALDI-TOF) m=z: 1050 [M]þ, 720 [C60]þ.
N-(2,4,6-Trinitrophenyl)-2-(2-nitrophenyl)fulleropyrrolidine
3c. UV-
1
vis(CHCl3) kmax: 257 (s), 320 (m), 431 (w)nm; H NMR (CS2=CDCl3, 600 MHz)
d: 8.77 (s, 2H), 8.05 (t, J ¼ 7.8 Hz, 2H), 7.58 (t, J ¼ 7.8 Hz, 1H), 7.50 (t, J ¼ 7.8 Hz,
1H), 7.13 (s, 1H), 5.56 (d, J ¼ 10.8 Hz, 1H), 5.45 (d, J ¼ 10.8, 1H) ppm; IR (KBr)
t: 3020, 2927, 2852, 1608, 1540, 1461, 1400, 1343, 1187, 1088, 858, 767, 737, 574,
562, 553, 527 cmꢁ1; MS (MALDI-TOF) m=z: 1096 [M þ H]þ, 720 [C60]þ.
N-(2,4,6-Trinitrophenyl)-2-(4-nitrophenyl)fulleropyrrolidine
3d. UV-
1
vis(CHCl3) kmax: 257 (s), 318 (m), 430 (w)nm; H NMR (CS2=CDCl3, 600 MHz)
d: 8.78 (s, 2H), 8.19 (d, J ¼ 9.0 Hz, 2H), 7.83 (d, J ¼ 9.0 Hz, 2H), 6.20 (s, 1H), 5.57
(d, J ¼ 10.8 Hz, 1H), 5.43 (d, J ¼ 10.8, 1H) ppm; IR (KBr) t: 3018, 2924, 2848,
1606, 1538, 1493, 1462, 1400, 1343, 1187, 1085, 860, 842, 729, 574, 562, 553,
527 cmꢁ1; MS (MALDI-TOF) m=z: 855 [M-(NO2)3C6H2NCH2]þ, 720 [C60]þ.

N-ARYLFULLEROPYRROLIDINE DERIVATIVES
585
N-(2,4,6-Trinitrophenyl)-2-phenylfulleropyrrolidine 3e. UV-vis(CHCl3)
1
max: 257 (s), 315 (m), 431 (w)nm; H NMR (CS2=CDCl3, 300 MHz) d: 8.73 (s,
k
2H), 7.55–7.52 (m, 2H), 7.32–7.28 (m, 3H), 6.06 (s, 1H), 5.56 (d, J ¼ 10.3 Hz, 1H),
5.39 (d, J ¼ 10.2, 1H) ppm; IR (KBr) t: 2923, 2851, 1605, 1537, 1456, 1403, 1338,
1183, 1085, 904, 877, 729, 705, 574, 563, 553, 527 cmꢁ1; MS (MALDI-TOF) m=z:
810 [M-(NO2)3C6H2NCH2]þ, 720 [C60]þ.
ACKNOWLEDGMENTS
We are grateful for financial support from the National Natural Science
Foundation of China (Project No. 10576026), Sichuan Bureau of Science and
Technology (Project No. 05GG009-018-05), and the Institute of Chemical
Materials, China Academy of Engineering Physics.
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