Metal-Free Synthesis of N-Alkyl-2,5-Unsubstituted/Monosubstituted Fulleropyrrolidines: Reaction of [60]Fullerene with Paraformaldehyde and Amines

Article abstract of DOI:10.1021/acs.joc.9b00083

A series of scarce N-alkyl-2,5-unsubstituted/monosubstituted fulleropyrrolidines were synthesized in moderate to excellent yields by the simple one-step thermal reaction of [60]fullerene with primary/secondary amines in the presence of paraformaldehyde without the addition of valuable metal salts. Intriguingly, the reaction with primary amines unexpectedly afforded N-alkyl-2,5-unsubstituted fulleropyrrolidines instead of the anticipated 2,5-monosubstituted fulleropyrrolidines. A plausible reaction pathway is proposed to elucidate the above-mentioned reaction process based on the experimental results.

Full text of DOI:10.1021/acs.joc.9b00083

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Article
Metal-Free Synthesis of N-Alkyl-2,5-Unsubstituted/
Monosubstituted Fulleropyrrolidines: Reaction of
[60]Fullerene with Paraformaldehyde and Amines
Yun-Fei Li, Duo Zhang, Hui-Juan Wang, Fa-Bao Li, Liang Sun,
Li Liu, Chao-Yang Liu, Abdullah M. Asiri, and Khalid A. Alamry
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b00083 • Publication Date (Web): 07 Feb 2019
Downloaded from http://pubs.acs.org on February 7, 2019
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Metal-Free Synthesis of N-Alkyl-2,5-Unsubstituted/Monosubstituted
Fulleropyrrolidines: Reaction of [60]Fullerene with
Paraformaldehyde and Amines
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†
†
‡
,†
†
†
Yun-Fei Li, Duo Zhang, Hui-Juan Wang, Fa-Bao Li,* Liang Sun, Li Liu,
,
‡
§
§
Chao-Yang Liu,* Abdullah M. Asiri, and Khalid A. Alamry
†Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials,
Ministry of Education Key Laboratory for the Synthesis and Application of Organic
Functional Molecules, Key Laboratory of Green Preparation and Application for
Functional Materials, Ministry of Education, and School of Chemistry and Chemical
Engineering, Hubei University, Wuhan 430062, People’s Republic of China
‡State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics,
Wuhan Center for Magnetic Resonance, Wuhan Institute of Physics and
Mathematics, Chinese Academy of Sciences, Wuhan 430071, People’s Republic of
China
§Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah
21589, Saudi Arabia
E-mail: lfb0615@hubu.edu.cn; chyliu@wipm.ac.cn
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____________________________________________________________________
R2
R2
R1
NH2
0
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N
R1
(
CH2O)n
air
21 examples
up to 65% yield
R4
,
R3
N
H
N
R4
free-metal
excellent yields
wide structural diversities
readily available starting materials
R3
8 examples
up to 51% yield
ABSTRACT:
A series of scarce N-alkyl-2,5-unsubstituted/monosubstituted fulleropyrrolidines were
synthesized in moderate to excellent yields by the simple one-step thermal reaction of
[60]fullerene with primary/secondary amines in the presence of paraformaldehyde
without the addition of valuable metal salts. Intriguingly, the reaction with primary
amines unexpectedly afforded N-alkyl-2,5-unsubstituted fulleropyrrolidines instead of
the anticipated 2,5-monosubstituted fulleropyrrolidines. A plausible reaction pathway
is proposed to elucidate the above-mentioned reaction process based on the
experimental results.
_
____________________________________________________________________
INTRODUCTION
Due to the outstanding properties,1,2 fullerenes as novel carbon materials have
received wide attention over the past 30 years. However, the poor solubility of
fullerenes in polar organic solvents and water has hampered their applications in
many fields. Therefore, the functionalization of fullerenes by chemical modification
to introduce versatile functional groups onto fullerene skeletons is an important aspect
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of fullerene research. By using chemical modification method,2,3 a large variety of
fullerene derivatives with structural and functional diversities have been prepared, of
which have displayed a broad range of valuable properties and have thus been utilized
in many fields including materials science, bio-medical application, and
1
1
1
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nanotechnology, exhibiting great advantages over traditional non-fullerene manners
4
in many cases. Although many synthetic strategies including cycloadditions,
nucleophilic additions, radical additions, and asymmetric catalysis have been
developed to functionalize fullerenes,2,3 the known protocols still meet a great
challenge in preparing N-alkyl-2,5-unsubstituted/monosubstituted fulleropyrrolidines.
Fulleropyrrolidines are a kind of important fullerene compound,3g,5-10 and have
attracted extensive attention among scientific community due to their promising
8
9
applications in many fields such as modern drug synthesis, organic solar cells, and
10
light-controlled field effect transistors. General speaking, fulleropyrrolidines were
synthesized by two main strategies, that is, the best-known Prato reaction5a,b together
with the newly-developed reaction based on aldehydes and amines.6f,7 However, these
known methods still have great difficulty in the preparation of fulleropyrrolidines with
specific structural motifs. For example, N-alkyl-2,5-unsubstituted/monosubstituted
fulleropyrrolidines is not easy to obtain by Prato reaction due to the very limited
6
b
substrate scope of N-substituted amino acids. To the best of our knowledge, only a
few N-alkyl-2,5-unsubstituted/monosubstituted fulleropyrrolidines were reported by
6
different groups. Nevertheless, these reported methods have their own limitations
including hardly available starting materials, poor product selectivity, low product
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yields, and complex reaction system. On the other hand, the substitutes on the
pyrrolidine ring were found to have a great correlation with the properties of
fulleropyrrolidines in many fields.5a,b Accordingly, the further exploration and
development of new synthetic methods for the preparation of scarce
N-alkyl-2,5-unsubstituted/monosubstituted fulleropyrrolidines in a straightforward
and practical manner with a broad substrate scope are still in strong demand.
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The newly-developed strategy to functionalize fullerenes by using inexpensive and
readily available aldehydes and amines6f,7,11-14 is a potential option due to its high
efficiency in preparing organofullerenes including fulleropyrrolidines,6f,7
fulleropyrrolines,11 tetrahydropyridinofullerenes,12 cyclopentafullerenes,13 and
1
4
fulleropyrrolidin-2-ols. In efforts to extend the reactions of [60]fullerene (C ) with
6
0
aldehydes and amines,6f,7,11-14 we found that the thermal reaction of C60 with
paraformaldehyde and benzylamine afforded N-benzyl-2,5-unsubstituted
fulleropyrrolidine instead of the expected N-unsubstituted-2-phenyl fulleropyrrolidine
Scheme 1). Considering the easy availability, inexpensive price, and versatility of
(
paraformaldehyde and primary amines, this above-mentioned synthetic route would
provide a potentially synthetic strategy to generate novel N-alkyl-2,5-unsubstituted
fulleropyrrolidines. In this paper, we reported the synthesis of scarce
N-alkyl-2,5-unsubstituted/monosubstituted fulleropyrrolidines in moderate to
excellent yields by a simple and efficient one-step reaction of C60 with
paraformaldehyde and primary/secondary amines without the use of expensive metal
salts.
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Scheme 1. Reaction of C with Paraformaldehyde and Benzylamine
6
0
failed
1
1
1
1
1
1
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1
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0
N
H
,
air
(
CH O)
NH2
2
n
N
RESULTS AND DISCUSSION
At the onset, paraformaldehyde and benzylamine (1a) were chosen as the model
substrates to screen the reaction conditions. To our disappointment, only a trace
amount of desired product 2a was obtained when the reaction of C60 with
paraformaldehyde and benzylamine (1a) was performed in a molar ratio of 1:5:5 in
o-dichlorobenzene (ODCB) at 180 °C for 120 min under air conditions (entry 1, Table
1
). To improve the yield of 2a, various reaction conditions have been examined. We
found the yield of 2a could be gradually improved from a trace amount to 61% when
the molar ratio of reaction was changed from 1:5:5 to 1:15:25 (entries 1-7, Table 1).
Further variation of the equivalents of paraformaldehyde and 1a had no benefit to the
yield of product 2a (entries 8-10, Table 1). Decreasing the reaction temperature
resulted in the obvious reduction in product yield (entry 11, Table 1). Almost the
same yield of 2a under nitrogen or dark conditions indicated that oxygen in air has no
influence on the reaction (entries 12 and 13, Table 1). Accordingly, the reagent molar
ratio of C , paraformaldehyde, and 1a as 1:15:25, the reaction temperature as 180 °C
6
0
together with the air conditions were selected as the optimized reaction conditions
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6
(entry 7, Table 1). It should be noted that the above-mentioned reaction with the
addition of 4-dimethylaminopyridine (DMAP), acetic acid (HOAc), and Mg(ClO4)2
were also examined due to the previous confirmation that their presence has the
positive effect on the formation of fulleropyrrolidines based on amines and
aldehydes.7a,e Unfortunately, no improvement for the yield of 2a could be observed
when the reaction was respectively conducted in the presence of DMAP, HOAc, and
Mg(ClO ) under the optimized conditions (entries 14-16, Table 1).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
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6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
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2
Table 1. Optimization of Reaction Conditions for the Reaction of C60 with
Paraformaldehyde and Benzylamine 1aa
additive
(
CH O)
NH2
N
2
n
Δ, air
1a
2
a
molar ratiob
o
yield (%) of 2ac
entry
additive
temp. ( C)
time (min)
1
2
none
none
none
none
none
none
none
none
none
none
none
none
none
DMAP
HOAc
1:5:5:0
180
180
180
180
180
180
180
180
180
180
160
180
180
180
180
180
120
45
30
35
32
40
20
20
30
15
40
20
20
25
25
25
trace
1:10:10:0
1:10:15:0
1:10:20:0
1:10:25:0
1:10:30:0
1:15:25:0
1:20:25:0
1:5:25:0
19 (59)
38 (54)
48 (98)
57 (86)
56 (86)
61 (84)
45 (75)
28 (82)
29 (38)
38 (75)
59 (69)
59 (71)
61 (84)
57 (80)
54 (98)
3
4
5
6
7
8
9
10
1:25:15:0
1:15:25:0
1:15:25:0
1:15:25:0
1:15:25:2
1:15:25:2
1:15:25:2
1
1
1
2d
3e
1
14
1
1
5
6
Mg(ClO
4
)
2
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aUnless otherwise indicated, all reactions were performed in o-dichlorobenzene (ODCB, 6 mL)
b
c
under air conditions. Molar ratio refers to C /(CH O) /1a/additive. Isolated yield; those in
6
0
2
n
parentheses were based on consumed C . dThe reaction was conducted under nitrogen
6
0
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
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3
3
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3
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3
4
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4
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4
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5
5
5
5
5
5
5
5
5
6
0
1
2
3
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5
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8
9
0
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2
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8
9
0
1
2
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4
5
6
7
8
9
0
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1
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3
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8
9
0
e
atmosphere. The reaction was performed in the dark.
With the reliable and optimal conditions in hand, we started to explore the scope of
arylmethanamines for this type of reaction. The reaction conditions and yields were
summarized in Table 2. As can be seen from Table 2, typical arylmethanamines
including benzylamines (1a-f) with both electron-donating and electron-withdrawing
groups, 2-thiophenemethylamine (1g), α-substituted benzylamines (1h,i), and
naphthylmethanamine (1j) could readily react with paraformaldehyde to produce the
desired N-alkyl-2,5-unsubstituted fulleropyrrolidines 2a-j in moderate to good yields.
In general, α-unsubstituted arylmethanamines (1a-g,j) displayed higher reaction
efficiency (30-65%) as compared with those bearing α-substitutes (1h,i) with yields of
1
6-23%. This observation could be explained by the great steric hindrance from
α-substituted benzylamines (1h,i). In addition, 2,4-dimethoxybenzylamine (1b) and
-chlorobenzylamine (1e) gave the obviously higher product yields (~65%) than other
2
arylmethanamines (1c,d,f), which should be attributed to the ortho-substitution effect.
Table 2. Reaction Conditions and Yields for the Reaction of C60 with
Paraformaldehyde and Arylmethanamines 1a
R
R
Ar
,
air
(CH2O)n
N
Ar
NH2
ODCB
1
2
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
b
amine 1
product 2
time (min)
20
yield (%)
NH2
2a
61 (84)
1a
NH2
OCH3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
b
15
15
65 (73)
1b
OCH3
NH2
53 (95)
51 (67)
1c
2c
OCH3
2
0
NH2
35
40 (62)
22 (67)
1d
2d
2e
Cl
2
0
NH2
Cl
25
64 (84)
1
e
NH2
1
f
2f
35
46 (96)
Br
1
g
2g
30
20
49 (94)
23 (82)
NH2
S
NH2
2
h
1
h
H
NH2
2i
20
15
16 (27)
30 (55)
1
i
NH2
2
j
1j
a
o
All reactions were performed in ODCB (6 mL) under air conditions at 180 C unless otherwise
b
indicated, molar ratio refers to C /(CH O) /1 = 1:15:25. Isolated yield, those in parentheses were
6
0
2
n
based on consumed C .
6
0
To expand the scope of the reaction, the substrates were further extended from
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arylmethanamines to other representative primary amines. The reaction conditions
and yields were listed in Table 3. As shown in Table 3,
electron-donating/withdrawing phenethylamines (3a-f), 2-thiophene ethylamine (3g),
3-phenyl-1-propylamine (3h), aliphatic amine (3i,j), and 2,2-diphenylethylamine (3k)
could readily react with paraformaldehyde to afford the expected fulleropyrrolidines
4a-k with yields of 21-65%. Compared with aryl/benzyl-substituted ethylamines
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
3a-h,k), alkyl-substituted ethylamines (3i,j) obviously decreased the product yields
21-36% vs 42-65%), probably due to the inherently low reactivity of 3i,j with an
(
inactive alkyl substituent in the current reaction system. Furthermore, the electronic
effect of substitutes on aryl ring had no obvious impact on product yields. For
instance, only slightly decreased product yields for electron-donating substituted 3b,c
were observed as compared with those for electron-withdrawing substituted 3d-f
(52-53% vs 53-57%). As for 2,2-diphenylethanamine (3k), its product yield was
remarkably increased as compared with that from aminodiphenylmethane (1h) by
adopting the similar reaction conditions (53% vs 23%), probably due to the lower
steric hindrance of 3k than 1h. It should be noted that aromatic amines including
aniline, 4-methoxyaniline, 3-methoxyaniline, 2-chloroaniline, and 4-chloroaniline
were also investigated under standard reaction conditions. However, no desired
product was detected probably due to the decreased nucleophilicity of NH by the
2
direct conjugation between the aryl and amine groups.
Table 3. Reaction Conditions and Yields for the Reaction of C60 with
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3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Paraformaldehyde and Inactive Amines 3a
R2
, air
R2
(
CH2O)n
N
NH2
ODCB
R1
3
R1
4
b
amine 3
product 4
time (min)
yield (%)
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
NH2
20
63 (93)
4
a
3a
1
5
53 (95)
NH2
4
b
15
35
53 (77)
52 (79)
3
b
OCH3
NH2
4
c
3c
H3CO
NH2
25
15
53 (79)
45 (98)
4
d
3d
Cl
NH2
4e
25
25
56 (70)
57 (98)
3
e
F
NH2
Cl
4
f
3f
Cl
NH2
4
g
20
15
42 (78)
52 (85)
S
3g
NH2
3
h
4h
4i
H3CO
NH2
20
15
36 (84)
21 (60)
3
i
NH2
4
j
3j
NH2
4
k
15
53 (90)
3k
a
o
All reactions were performed in ODCB (6 mL) under air conditions at 180 C unless otherwise
b
indicated, molar ratio refers to C /(CH O) /3 = 1:15:25. Isolated yield, those in parentheses were
6
0
2
n
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based on consumed C .
6
0
It is worth to mention that some controlled experiments were conducted to test the
effect of substituents on the reaction rate with primary amines. Representative
benzylamine (1a), 4-methoxybenzylamine (1c), and 4-chlorobenzylamine (1d) as well
as typical phenethylamine (4a), 4-methoxyphenethylamine (4b), and
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
4
-chlorophenethylamine (4d) were selected as model substrates to react with C and
60
paraformaldehyde under the optimized reaction conditions for 20 min and 15 min,
respectively. Experimental results indicated that electron-donating substituted
4
-methoxybenzylamine (1c) and 4-methoxyphenethylamine (4b) exhibited the
obviously higher reaction rate than the corresponding electron-withdrawing
substituted 4-chlorobenzylamine (1d) and 4-chlorophenethylamine (4d) by comparing
with their consumption of C probably due to the higher nucleophilicity of NH from
6
0
2
amines 1c and 4b as compared to 1d and 4d. As for the unsubstituted benzylamine
1a) and phenethylamine (4a), the reaction rate is between electron-donating 1c,4b
(
and electron-withdrawing 1d,4d, agreeing well with their nucleophilic ability.
Secondary amines were also applied to the above-mentioned reaction system. We
first studied the reaction with N-methylbenzylamine (5a), N-ethylbenzylamine (5b),
N,N-dibenzylamine (5c), diethylamine (5d), dipropylamine (5e), and dibutylamine
(5f) under the optimized reaction conditions. Experimental results indicated that all of
the six representative amines could react with paraformaldehyde to generate the
desired N-alkyl-2-substituted fulleropyrrolidines 6a-f with yields of 31-51% (Table
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2
3
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6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
4). It should be noted that two fulleropyrrolidine isomers should be theoretically
formed for unsymmetrical amines (5a,b). However, only the N-alkyl-2-phenyl
fulleropyrrolidines instead of N-benzyl-2-alkyl fulleropyrrolidines were
experimentally obtained, probably due to the higher reactivity at the benzylic position
of 5a,b. Unsymmetrical ethylbutylamine (5g) was also investigated and both
N-butyl-2-methyl fulleropyrrolidine (6g) and N-ethyl-2-propyl fulleropyrrolidine (6g')
were isolated with yields of 25% and 18%, respectively (Scheme2). The lower yield
of 6g' as compared to 6g might be ascribed to the great steric hindrance of propyl
group relative to methyl group in 5g. It is worth to mention that the relatively high
reaction rate for primary/secondary amines 1/3/5 was probably due to the less steric
hindrance of paraformaldehyde relative to other aldehydes.7c,f
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Table 4. Reaction Conditions and Yields for the Reaction of C60 with
Paraformaldehyde and Secondary Amines 5a
R2
, air
(CH O)
R1
N
R2
2
n
N
H
5
R1
6
R1 = phenyl for 6a-c
b
amine 5
product 6
time (min)
25
yield (%)
N
H
5a
6a
31 (97)
N
H
5
b
6b
6c
6d
6e
15
15
15
15
51 (94)
40 (98)
42 (95)
36 (78)
N
H
5c
N
H
5
d
e
N
H
5
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N
H
5f
6f
15
33 (77)
a
o
All reactions were performed in ODCB (6 mL) under air conditions at 180 C unless otherwise
b
indicated, molar ratio refers to C /(CH O) /5 = 1:15:25. Isolated yield, those in parentheses were
6
0
2
n
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
based on consumed C .
6
0
Scheme 2. Reaction of C with Paraformaldehyde and Ethylbutylamine 5g
6
0
80 oC, 15 min
ODCB, air
1
(
CH2O)n
N
H
5
g
N
N
6
g
6g'
18%
25%
Fulleropyrrolidines 2a,6b,d-fc,6d,ee, g, h, 4a, b, e, j, and 6a, b, c, d are
known compounds, and their identities were confirmed by comparison of their
spectral data with those reported previously in the literature. As for new compounds
6f 6f 6e
6e 6e 6e 6f
6a 6c 6b 6b
2
b,d,f,i,j, 4c,d,f-i,k, and 6e-g,g', their structures were unambiguously characterized
by their MALDI-TOF MS, FT-IR, UV-vis, H and 13C NMR spectra. All
1
−
MALDI-TOF MS of these new compounds gave the correct [M] peaks. FT-IR
spectra exhibited the characteristic absorptions of C60 skeleton at about 527, 574,
-
1
1184, and 1427 cm . Their UV-vis spectra showed a diagnostic absorption at 431 nm
for the 1,2-adducts of C . Expected chemical shifts and splitting patterns for all
6
0
1
13
protons were also displayed in their H NMR spectra. In their C NMR spectra,
2
2
b,d,f,j and 4c,d,f-i,k exhibited no more than 16 lines for the 58 sp -carbons of the
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2
3
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5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3
C skeleton and one peak at 69.23-69.74 ppm for the two sp -carbons of the C cage,
6
0
60
agreeing well with their C molecular symmetry, whereas 2i displayed 23 lines
2
v
2
including some overlapping ones for the 58 sp -carbons of the C moiety and one
6
0
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
peak at 69.28 ppm for the two sp -carbons of the C skeleton, consistent with its C
s
6
0
symmetry. As for 6e-g,g', there were at least 44 peaks including some overlapped
2
ones for the 58 sp -carbons of the C cage, agreeing well with the C symmetry of
6
0
1
their molecular structures.
7
On the basis of the previously reported mechanisms together with the
experimental observations, we proposed a plausible reaction pathway for the
formation of N-alkyl-2,5-unsubstituted/monosubstituted fulleropyrrolidines 2/4/6. As
depicted in Scheme 3, paraformaldehyde first reacts with amines 1/3/5 to produce a
2
bis-hydroxymethylation intermediate I (R = H) or a mono-hydroxymethylation
2
intermediate IX (R = alkyl). In the case of intermediate I, a subsequent
dehydrogenation with the aid of an excess of 1/3 as a base leads to the formation of an
anionic intermediate II. It is worth mentioning that the preferred dehydrogenation site
of intermediate I is located in the α-hydrogen rather than more acidic hydroxyl
hydrogen probably due to the existence of two OH···O intramolecular hydrogen
bonds between two hydroxyl groups (OH), which can increase the stability of
hydroxyl hydrogen. Protonation of intermediate II by the proton delivery of base·H+
to the OH group produces a 1,2-dipole III or a 1,3-dipole IV accompanied by the
elimination of one molecule of H O. Cycloaddition of III or IV to C generates a
2
60
fulleropyrrolidin-2-ol intermediate V, followed by dehydration by the same way as for
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intermediate II to produce an iminium intermediate VI. Subsequent hydride transfer
from amines 1/3 to VI forms N-alkyl-2,5-unsubstituted fulleropyrrolidines 2/4 as well
as another iminium intermediate VII, which can undergo deprotonation and
subsequent hydrolysis to attain an aldehyde intermediate VIII. The successful
detection of benzaldehyde (see Figure S1 in Supporting Information) from the
reaction mixture of C , paraformaldehyde, and benzylamine (1a) for 20 min under
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
6
0
the optimized conditions confirms the plausibility of the above-mentioned reaction
pathway although the existence of benzaldehyde in the reaction solution is quite low
probably due to the further condensation reaction of benzaldehyde with benzylamine.
As for intermediate IX, dehydration under the assistance of 5 results in the generation
of a 1,2-dipole X or a 1,3-dipole XI, followed by a concerted 1,3-dipolar
cycloaddition to C to give N-alkyl-2-substituted fulleropyrrolidines 6.
6
0
Scheme 3. Possible Formation Mechanism for Fulleropyrrolidines 2/4/6
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1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
protonation
base
R2 = H
1/3 as base
H
N
R1
O
N
R1
O
H
O
H
O
R1
alkyl
aryl
I
H
H2O
=
II
H
H
H
hydrogen bond
hydrogen bond
OH
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
C60
base H
HO
N
H
HO
N
H
N
R1
H O
2
III
IV
R1
R1
R2
V
R1
N
1
/3/5
H
(CH O)
2
n
H
heating
R1
1/3
H N
2
N
N
R1
R1
1 VII
R
H N
2
VI
2/4
H
H
H O
2
R1
R1 VIII
HN
O
OH
H
R2 = alkyl
alkyl
5 as base
R1
R1
R1
H
N
H
N
R2
X
H
N
H O
2
R1
=
R2
IX
R2
XI
aryl
C60
R2
N
R1
6
Besides the detection experiments of benzaldehyde from the reaction mixture of
C , paraformaldehyde, and benzylamine (1a) under standard reaction conditions,
6
0
other controlled experiments by utilizing the reaction of C with paraformaldehyde
6
0
and 1a in the presence/absence of tert-butylamine were also carried out under various
conditions (Table 5). We first investigated the reaction of C with paraformaldehyde
6
0
and tert-butylamine in the absence of 1a, and found that no desired
N-tert-butyl-2,5-unsubstituted fulleropyrrolidine was formed even by increasing the
amount of tert-butylamine and prolonging the reaction time (entries 1 and 2, Table 5),
agreeing well with our suggested reaction mechanism because the reduction of
iminium VI by hydrogen transfer to produce the expected fulleropyrrolidine was
hampered when tert-butylamine without α-hydrogen was employed. Furthermore, we
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also studied the reaction of C with paraformaldehyde and 1a in a molar ratio of
6
0
1
:15:8 (entry 3, Table 5). The reduction of the equivalent of 1a from 25 to 8 could
meet the molar ratio of paraformaldehyde to 1a as 2:1 based on our proposed
mechanism. However, the yield of 2a was found to be dramatically reduced from 61%
to 9% (entry 7, Table 1 vs entry 3, Table 5), indicating that an excess of 1a might
have multiple roles in the high efficient synthesis of 2a. On the basis of the successful
detection of benzaldehyde from the reaction mixture of C , paraformaldehyde, and
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
6
0
1
a under the optimized conditions (see Figure S1 in Supporting Information), 1a as a
reductant to result in the generation of 2a has been well established. Additionally, 1a
as a base might be another major reason for the synthesis of 2a with a high yield.
Controlled experiments indicated that the addition of tert-butylamine could improve
the yield of 2a from 9% to 30% (entries 4-8, Table 5), showing that the presence of a
base had a positive effect on the formation of 2a. It is worth to mention that a large
excess of tert-butylamine was required probably due to its low boiling point (about 45
oC). Based on the above experimental facts, 1a might serve as reactant, reductant, and
organic base, consistent with our suggested mechanism shown in Scheme 3. It should
be noted that controlled experiments by increasing the amount of paraformaldehyde
(from 15 to 40 equiv.) were also conducted. Experimental results indicated that the
yield of 2a could be gradually decreased from 9% to 5% (entries 3 and 9-11, Table 5),
excluding the possibility of paraformaldehyde as a reductant to afford product 2a.
Table 5. Controlled Experiments for Mechanistic Studya
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6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
additive
(
CH2O)n
NH2
N
Δ, air
1a
2
a
molar ratiob
yield (%) of 2ac
entry
additive
time (min)
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
(CH
3
3
)
3
3
CNH
CNH
2
2
1:15:0:25
1:15:0:50
1:15:8:0
240
300
30
40
35
35
35
35
30
25
20
none
none
(CH
)
3
none
9 (22)
13 (29)
23 (70)
25 (77)
30 (73)
29 (75)
8 (18)
7 (14)
5 (8)
4
(CH
(CH
(CH
(CH
(CH
3
3
3
3
3
)
3
)
3
)
3
)
3
)
3
CNH
CNH
CNH
CNH
CNH
2
2
2
2
2
1:15:8:10
1:15:8:20
1:15:8:30
1:15:8:40
1:15:8:50
1:20:8:0
5
6
7
8
9
none
none
none
10
1:30:8:0
1
1
1:40:8: 0
a
o
Unless otherwise indicated, all reactions were performed at 180 C in ODCB (6 mL) under air
conditions. Molar ratio refers to C /(CH O) /1a/(CH ) CNH . cIsolated yield; those in
b
6
0
2
n
3 3
2
parentheses were based on consumed C .
6
0
CONCLUSION
In summary, the simple one-step thermal reaction of C with paraformaldehyde and
6
0
primary/secondary amines in the absence of metal salts successfully afforded a series
of scarce N-alkyl-2,5-unsubstituted/monosubstituted fulleropyrrolidines in moderate
to excellent yields. The current method for the preparation of fulleropyrrolidines by
using inexpensive and easily available paraformaldehyde and primary/secondary
amines is obviously more straightforward and practical than the previous ones.6
Furthermore, the current synthetic protocol also displays a broad substrate scope and
excellent functional group tolerance, providing a good opportunity for researchers to
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design and synthesize a large variety of novel organic photovoltaic materials. An
unusual mechanism for the formation of N-alkyl-2,5-unsubstituted fulleropyrrolidines
was suggested by utilizing primary amines as reactant, reductant, and organic base
based on our experimental observations.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
EXPERIMENTAL SECTION
General Methods. Reagents and solvents employed were commercially available
without further purification. Purified fullerene products were obtained by flash
chromatography over silica gel. The UV-vis spectra were performed in CHCl . IR
3
1
13
spectra were taken with KBr pellets. NMR spectra ( H and C NMR) were recorded
1
on a 500 or 800 MHz NMR spectrometer. Chemical shifts in H NMR spectra were
1
3
referenced to tetramethylsilane (TMS) at 0.00 ppm, while chemical shifts in C NMR
spectra were referenced to residual DMSO at 39.52 ppm. High-resolution mass
spectrometry
-hydroxy-α-cyanocinnamic acid as the matrix in negative-ion mode.
General Synthetic Procedure for Fulleropyrrolidines 2/4/6. C (36.0 mg, 0.05
(HRMS)
by
MALDI-TOF
was
obtained
by
using
4
6
0
mmol), paraformaldehyde (22.5 mg, 0.75 mmol) and amines 1/3/5 (1.25 mmol) were
added to a 50 mL round-bottom flask equipped with a reflux condenser and a
magnetic stirrer. After they were completely dissolved in 6 mL of o-dichlorobenzene
o
(
ODCB) by sonication, the resulting solution was put into an oil bath preset at 180 C
and stirred under air conditions. Thin-layer chromatography (TLC, CS /CH Cl as
2
2
2
developing solvent, R (C ) = 1.0) was employed to carefully monitor the reaction
f
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1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
and to stop the reaction at the designated time. The reaction mixture was filtered
through a silica gel plug to remove any insoluble material. After the solvent
evaporation in vacuo was completed, the residue was separated on a silica gel column
with carbon disulfide/dichloromethane as the eluent to afford first unreacted C and
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
6
0
then fulleropyrrolidines 2/4/6.
Fulleropyrrolidine 2a: According to the general synthetic procedure, the reaction of
C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 1a (137
6
0
o
μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 20 min afforded first unreacted C
6
0
(9.8 mg, 27%) and then 2a6b,d-f (26.2 mg, 61%, R = 0.3) as amorphous brown solid
f
with CS as the eluent: mp > 300 °C.
2
Fulleropyrrolidine 2b: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 1b
6
0
o
(
185 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 15 min afforded first unreacted
C (4.1 mg, 11%) and then 2b (29.7 mg, 65%, R = 0.1) as amorphous brown solid
6
0
f
1
with CS /CH Cl as the eluent (V/V = 10/1): mp > 300 °C. 2b: H NMR (800 MHz,
2
2
2
CS /DMSO-d ) δ 7.51 (d, J = 8.3 Hz, 1H), 6.49 (dd, J = 8.3, 2.0 Hz, 1H), 6.46 (d, J =
2
6
1
3
1
2
.0 Hz, 1H), 4.38 (s, 4H), 4.21 (s, 2H), 3.91 (s, 3H), 3.79 (s, 3H); C{ H} NMR (125
MHz, CS /DMSO-d ) (all 4C unless indicated) δ 159.47 (1C, aryl C), 157.65 (1C, aryl
2
6
C), 154.32, 146.21 (2C), 145.23, 145.20, 145.00, 144.70 (2C), 144.42, 144.23,
1
43.56, 142.07 (2C), 141.60, 141.29, 141.07, 140.87, 139.15, 135.38, 130.33 (1C,
3
aryl C), 116.60 (1C, aryl C), 103.91 (1C, aryl C), 97.96 (1C, aryl C), 69.74 (2C, sp -C
-1
of C ), 66.13 (2C), 54.52 (1C), 54.27 (1C), 50.49 (1C); FT-IR ν/cm (KBr) 2922,
6
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2852, 1608, 1583, 1510, 1459, 1418, 1331, 1286, 1266, 1206, 1184, 1155, 1108,
1
034, 831, 768, 638, 574, 526; UV-vis (CHCl ) λmax/nm 257, 305, 431; HRMS
3
−
(
MALDI-TOF) m/z: [M] Calcd for C H NO 913.1103; Found 913.1093.
7
1
15
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
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5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Fulleropyrrolidine 2c: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 1c
6
0
o
(163 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 15 min afforded first unreacted
6
d,e
C (15.8 mg, 44%) and then 2c
(23.2 mg, 53%, R = 0.3) as amorphous brown
f
6
0
solid with CS /CH Cl as the eluent (V/V = 10/1): mp > 300 °C.
2
2
2
Fulleropyrrolidine 2d: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 1d
6
0
o
(152 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 35 min afforded first unreacted
C (12.7 mg, 35%) and then 2d (17.9 mg, 40%, R = 0.7) as amorphous brown solid
6
0
f
1
with CS as the eluent: mp > 300 °C. 2d: H NMR (500 MHz, CS /DMSO-d ) δ 7.61
2
2
6
1
3
1
(d, J = 8.4 Hz, 2H), 7.37 (d, J = 8.4 Hz, 2H), 4.40 (s, 4H), 4.25 (s, 2H); C{ H} NMR
(
125 MHz, CS /DMSO-d ) (all 4C unless indicated) δ 153.85, 146.19 (2C), 145.18,
2
6
145.05, 144.98, 144.61 (2C), 144.42, 144.20, 143.50, 142.04 (2C), 141.58, 141.19,
1
41.02, 140.84, 139.14, 135.70 (1C, aryl C), 135.28, 132.51 (1C, aryl C), 129.26 (2C,
3
aryl C), 128.00 (2C, aryl C), 69.58 (2C, sp -C of C ), 66.43 (2C), 57.05 (1C); FT-IR
6
0
-1
ν/cm (KBr) 2917, 2850, 1508, 1487, 1464, 1426, 1336, 1183, 1156, 1088, 1013,
8
93, 805, 769, 669, 574, 527; UV-vis (CHCl ) λmax/nm 256, 307, 431; HRMS
3
−
(MALDI-TOF) m/z: [M] Calcd for C H ClN 887.0502; Found 887.0502.
6
9
10
Fulleropyrrolidine 2e: According to the general synthetic procedure, the reaction
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5
6
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 1e
6
0
o
(
151 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 25 min afforded first unreacted
6f
C (8.7 mg, 24%) and then 2e (28.6 mg, 64%, R = 0.6) as amorphous brown solid
6
0
f
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
with CS as the eluent: mp > 300 °C.
2
Fulleropyrrolidine 2f: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 1f
6
0
o
(
158 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 35 min afforded first unreacted
C (18.6 mg, 52%) and then 2f (21.2 mg, 46%, R = 0.4) as amorphous brown solid
6
0
f
1
with CS as the eluent: mp > 300 °C. 2f: H NMR (800 MHz, CS /DMSO-d ) δ 7.55
2
2
6
1
3
1
(
d, J = 8.4 Hz, 2H), 7.51 (d, J = 8.4 Hz, 2H), 4.40 (s, 4H), 4.23 (s, 2H); C{ H} NMR
(125 MHz, CS /DMSO-d ) (all 4C unless indicated) δ 153.89, 146.22 (2C), 145.21,
2
6
1
1
45.08, 145.01, 144.64 (2C), 144.45, 144.23, 143.53, 142.07 (2C), 141.60, 141.22,
41.05, 140.87, 139.17, 136.25 (1C, aryl C), 135.31, 130.98 (2C, aryl C), 129.63 (2C,
3
aryl C), 120.90 (1C, aryl C), 69.62 (2C, sp -C of C ), 66.45 (2C), 57.10 (1C); FT-IR
6
0
-1
ν/cm (KBr) 2916, 2850, 1511, 1485, 1427, 1338, 1185, 1154, 1113, 1069, 1011,
803, 768, 574, 527; UV-vis (CHCl ) λmax/nm 256, 307, 431; HRMS (MALDI-TOF)
3
−
m/z: [M] Calcd for C H BrN 930.9997; Found 930.9997.
6
9
10
Fulleropyrrolidine 2g: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 1g
6
0
o
(
128 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 30 min afforded first unreacted
6
f
C (17.4 mg, 48%) and then 2g (21.0 mg, 49%, R = 0.3) as amorphous brown solid
6
0
f
with CS as the eluent: mp > 300 °C.
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Fulleropyrrolidine 2h: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 1h
6
0
o
(
215 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 20 min afforded first unreacted
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
6e
C (26.0 mg, 72%) and then 2h (10.9 mg, 23%, R = 0.85) as amorphous brown
6
0
f
solid with CS as the eluent: mp > 300 °C.
2
Fulleropyrrolidine 2i: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 1i
6
0
o
(
159 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 20 min afforded first unreacted
C (14.3 mg, 40%) and then 2i (6.8 mg, 16%, R = 0.5) as amorphous brown solid
6
0
f
1
with CS as the eluent: mp > 300 °C. 2i: H NMR (800 MHz, CS /DMSO-d ) δ 7.62
2
2
6
(dd, J = 8.1, 1.2 Hz, 2H), 7.37 (t, J = 7.7 Hz, 2H), 7.27 (t, J = 7.4 Hz, 1H), 4.43 (d, J =
8
3
.5 Hz, 2H ), 4.28 (d, J = 8.5 Hz, 2H ), 3.92 (q, J = 6.6 Hz, 1H), 1.80 (d, J = 6.6 Hz,
13
1
H ); C{ H} NMR (125 MHz, CS /DMSO-d ) (all 2C unless indicated) δ 154.07,
2
6
154.03, 146.18, 145.16 (4C), 145.11, 145.06, 144.97 (4C), 144.63, 144.41, 144.39,
44.18 (4C), 143.51, 143.50, 143.20 (1C, aryl C), 142.02, 141.55 (4C), 141.23,
1
141.18, 141.01 (4C), 140.83, 140.81, 139.13, 139.11, 135.33 (4C), 128.05 (aryl C),
3
1
26.77 (1C, aryl C), 126.25 (aryl C), 69.28 (sp -C of C ), 65.26, 62.96 (1C), 22.55
6
0
-1
(
1C); FT-IR ν/cm (KBr) 2920, 2851, 1429, 1182, 1153, 1122, 1024, 699, 527,
−
UV-vis (CHCl ) λ /nm 257, 305, 431; HRMS (MALDI-TOF) m/z: [M] Calcd for
3
max
C H N 867.1048; Found 867.1048.
7
0
13
Fulleropyrrolidine 2j: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 1j
6
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1
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1
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1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
o
(183 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 15 min afforded first unreacted
C (16.3 mg, 45%) and then 2j (13.4 mg, 30%, R = 0.8) as amorphous brown solid
6
0
f
1
with CS as the eluent: mp > 300 °C. 2j: H NMR (500 MHz, CS /DMSO-d ) δ 8.63
2
2
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(d, J = 8.4 Hz, 1H ), 7.84 (d, J = 8.2 Hz, 1H), 7.82 (d, J = 8.4 Hz, 1H), 7.78 (d, J = 6.8
Hz, 1H), 7.57 (t, J = 7.5 Hz, 1H), 7.48 (t, J = 7.3 Hz, 2H), 4.70 (s, 2H), 4.48 (s, 4H);
1
3
1
C{ H} NMR (125 MHz, CS /DMSO-d ) (all 4C unless indicated) δ 153.55, 145.70
2
6
(
2C), 144.68, 144.62, 144.49, 144.14 (2C), 143.91, 143.71, 143.02, 141.54 (2C),
41.07, 140.74, 140.54, 140.34, 138.64, 134.78, 132.64 (1C, aryl C), 132.36 (1C, aryl
C), 130.94 (1C, aryl C), 127.56 (1C, aryl C), 127.47 (1C, aryl C), 125.74 (1C, aryl C),
25.00 (1C, aryl C), 124.90 (1C, aryl C), 124.33 (1C, aryl C), 123.42 (1C, aryl C),
1
1
3
-1
69.23 (2C, sp -C of C ), 66.31 (2C), 55.74 (1C); FT-IR ν/cm (KBr) 2899, 2779,
6
0
1
509, 1462, 1426, 1335, 1268, 1166, 1111, 1074, 892, 791, 779, 768, 574, 527,
−
UV-vis (CHCl ) λ /nm 257, 305, 431; HRMS (MALDI-TOF) m/z: [M] Calcd for
3
max
C H N 903.1048; Found 903.1044.
7
3
13
Fulleropyrrolidine 4a: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 3a
6
0
o
(
157 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 20 min afforded first unreacted
6e
C (11.4 mg, 32%) and then 4a (27.4 mg, 63%, R = 0.2) as amorphous brown solid
6
0
f
with CS as the eluent: mp > 300 °C.
2
Fulleropyrrolidine 4b: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 3b
6
0
o
(
183 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 15 min afforded first unreacted
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C (11.2 mg, 31%) and then 4b (23.7 mg, 53%, R = 0.3) as amorphous brown solid
6
0
f
with CS /CH Cl as the eluent (V/V = 10/1): mp > 300 °C.
2
2
2
Fulleropyrrolidine 4c: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 3c
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
6
0
o
(
183 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 35 min afforded first unreacted
C (12.2 mg, 34%) and then 4c (23.3 mg, 52%, R = 0.3) as amorphous brown solid
6
0
f
1
with CS /CH Cl as the eluent (V/V = 10/1): mp > 300 °C. 4c: H NMR (500 MHz,
2
2
2
CS /DMSO-d ) δ 7.15 (t, J = 7.8 Hz, 1H), 6.90 (t, J = 7.6 Hz, 2H), 6.67 (d, J = 8.0
2
6
Hz, 1H), 4.43 (s, 4H), 3.76 (s, 3H), 3.30 (t, J = 7.8 Hz, 2H), 3.15 (t, J = 7.8 Hz, 2H);
1
3
1
C{ H} NMR (125 MHz, CS /DMSO-d ) (all 4C unless indicated) δ 158.72 (1C, aryl
2
6
C), 154.07, 146.16 (2C), 145.15, 145.11, 144.95, 144.62 (2C), 144.38, 144.18,
1
1
43.50, 142.03 (2C), 141.55, 141.18, 141.02, 140.82, 140.39 (1C, aryl C), 139.10,
35.28, 128.61 (1C, aryl C), 120.34 (1C, aryl C), 113.89 (1C, aryl C), 110.94 (1C,
3
aryl C), 69.63 (2C, sp -C of C ), 66.88 (2C), 55.41 (1C), 54.00 (1C), 34.85 (1C);
6
0
-1
FT-IR ν/cm (KBr) 2927, 1584, 1487, 1462, 1453, 1429, 1343, 1259, 1188, 1156,
1115, 1057, 873, 768, 696, 575, 527; UV-vis (CHCl ) λmax/nm 257, 306, 431; HRMS
3
−
(
MALDI-TOF) m/z: [M] Calcd for C H NO 897.1154; Found 897.1154.
7
1
15
Fulleropyrrolidine 4d: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 3d
6
0
o
(
176 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 25 min afforded first unreacted
C (11.9 mg, 33%) and then 4d (23.7 mg, 53%, R = 0.5) as amorphous brown solid
6
0
f
1
with CS as the eluent: mp > 300 °C. 4d: H NMR (500 MHz, CS /DMSO-d ) δ 7.35
2
2
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1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(d, J = 8.0 Hz, 2H), 7.25 (d, J = 8.0 Hz, 2H), 4.44 (s, 4H), 3.30 (t, J = 7.6 Hz, 2H),
1
3
1
3
.18 (t, J = 7.6 Hz, 2H); C{ H} NMR (125 MHz, CS /DMSO-d ) (all 4C unless
2 6
indicated) δ 154.00, 146.18 (2C), 145.17, 145.09, 144.97, 144.63 (2C), 144.40,
144.20, 143.51, 142.05 (2C), 141.58, 141.19, 141.03, 140.84, 139.13, 137.60 (1C,
aryl C), 135.25, 131.31 (1C, aryl C), 129.59 (2C, aryl C), 127.74 (2C, aryl C), 69.62
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
-1
(2C, sp -C of C ), 66.83 (2C), 53.20 (1C), 34.08 (1C); FT-IR ν/cm (KBr) 2920,
6
0
2
5
850, 1581, 1489, 1466, 1426, 1384, 1183, 1159, 1115, 1091, 813, 769, 597, 574,
−
27; UV-vis (CHCl ) λ /nm 256, 306, 431; HRMS (MALDI-TOF) m/z: [M] Calcd
3
max
for C H ClN 901.0658; Found 901.0658.
7
0
12
Fulleropyrrolidine 4e: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 3e
6
0
o
(
164 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 25 min afforded first unreacted
6e
C (7.2 mg, 20%) and then 4e (25.0 mg, 56%, R = 0.2) as amorphous brown solid
6
0
f
with CS as the eluent: mp > 300 °C.
2
Fulleropyrrolidine 4f: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 3f
6
0
o
(
188 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 25 min afforded first unreacted
C (15.1 mg, 42%) and then 4f (26.8 mg, 57%, R = 0.4) as amorphous brown solid
6
0
f
1
with CS as the eluent: mp > 300 °C. 4f: H NMR (500 MHz, CS /DMSO-d ) δ 7.50
2
2
6
(d, J = 8.2 Hz, 1H), 7.37 (d, J = 2.0 Hz, 1H), 7.23 (dd, J = 8.2, 2.0 Hz, 1H), 4.47 (s,
1
3
1
4H), 3.31 (s, 4H); C{ H} NMR (125 MHz, CS /DMSO-d ) (all 4C unless indicated)
2
6
δ 153.94, 146.16 (2C), 145.15, 145.05, 144.95, 144.61 (2C), 144.38, 144.17, 143.48,
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142.02 (2C), 141.55, 141.16, 141.01, 140.82, 139.10, 135.29 (1C, aryl C), 135.23,
1
1
33.97 (1C, aryl C), 132.10 (1C, aryl C), 131.34 (1C, aryl C), 128.30 (1C, aryl C),
3
26.39 (1C), 69.60 (2C, sp -C of C ), 66.76 (2C), 53.22 (1C), 31.59 (1C); FT-IR
6
0
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
-1
ν/cm (KBr) 2921, 2849, 1512, 1470, 1427, 1343, 1184, 1163, 1115, 1103, 1051,
8
97, 864, 816, 769, 574, 527; UV-vis (CHCl ) λmax/nm 255, 307, 431; HRMS
3
−
(MALDI-TOF) m/z: [M] Calcd for C H Cl N 935.0269; Found 935.0269.
7
0
11
2
Fulleropyrrolidine 4g: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 3g
6
0
o
(146 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 20 min afforded first unreacted
C (16.6 mg, 46%) and then 4g (18.5 mg, 42%, R = 0.3) as amorphous brown solid
6
0
f
1
with CS as the eluent: mp > 300 °C. 4g: H NMR (500 MHz, CS /DMSO-d ) δ 7.13
2
2
6
(d, J = 4.6 Hz, 1H), 6.97 (s, 1H), 6.91 (t, J = 3.7 Hz, 1H), 4.48 (s, 4H), 3.42 (t, J = 6.4
13
1
Hz, 2H), 3.37 (t, J = 6.4 Hz, 2H); C{ H} NMR (125 MHz, CS /DMSO-d ) (all 4C
2
6
unless indicated) δ 153.83, 146.01 (2C), 144.99, 144.93, 144.80, 144.47 (2C), 144.23,
1
44.02, 143.34, 141.87 (2C), 141.40, 141.04 (5C), 140.87, 140.67, 138.95, 135.15,
3
125.84 (1C, aryl C), 124.25 (1C, aryl C), 123.22 (1C, aryl C), 69.45 (2C, sp -C of
-1
C ), 66.66 (2C), 55.09 (1C), 28.79 (1C); FT-IR ν/cm (KBr) 2921, 2849, 1515, 1466,
6
0
1
428, 1382, 1344, 1183, 1161, 1116, 847, 819, 769, 694, 574, 527; UV-vis (CHCl3)
−
λmax/nm 256, 305, 431; HRMS (MALDI-TOF) m/z: [M] Calcd for C H NS
68
11
8
73.0612; Found 873.0612.
Fulleropyrrolidine 4h: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 3h
6
0
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8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
o
(178 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 15 min afforded first unreacted
C (13.7 mg, 39%) and then 4h (22.9 mg, 52%, R = 0.25) as amorphous brown solid
6
0
f
1
with CS as the eluent: mp > 300 °C. 4h: H NMR (500 MHz, CS /DMSO-d ) δ
2
2
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
7.27-7.21 (m, 4H), 7.12 (t, J = 7.0 Hz, 1H), 4.38 (s, 4H), 3.06 (t, J = 7.1 Hz, 2H), 2.95
1
3
1
(
t, J = 7.1 Hz 2H), 2.24-2.19 (m, 2H); C{ H} NMR (125 MHz, CS /DMSO-d ) (all
2 6
4C unless indicated) δ 153.93, 146.00 (2C), 144.99, 144.95, 144.80, 144.46 (2C),
44.22, 144.02, 143.34, 141.87 (2C), 141.40, 141.05, 140.86, 140.67, 140.48 (1C,
1
aryl C), 138.96, 135.09, 127.62 (2C, aryl C), 127.52 (2C, aryl C), 125.03 (1C, aryl C),
3
69.46 (2C, sp -C of C ), 66.63 (2C), 52.69 (1C), 32.77 (1C), 29.59 (1C); FT-IR
6
0
-1
ν/cm (KBr) 2880, 1510, 1450, 1426, 1340, 1184, 1115, 897, 769, 745, 696, 597,
574, 527; UV-vis (CHCl ) λ /nm 256, 306, 431; HRMS (MALDI-TOF) m/z: [M]−
3
max
Calcd for C H N 881.1205; Found 881.1205.
7
1
15
Fulleropyrrolidine 4i: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 3i
6
0
o
(
109 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 20 min afforded first unreacted
C (20.6 mg, 57%) and then 4i (14.7 mg, 36%, R = 0.08) as amorphous brown solid
6
0
f
1
with CS /CH Cl as the eluent (V/V = 10/1): mp > 300 °C. 4i: H NMR (500 MHz,
2
2
2
CS /DMSO-d ) δ 4.46 (s, 4H), 3.86 (t, J = 5.2 Hz, 2H), 3.46 (s, 3H), 3.26 (t, J = 5.2
2
6
Hz, 2H); 13C{ H} NMR (125 MHz, CS /DMSO-d ) (all 4C unless indicated) δ
1
2
6
1
54.06, 146.03 (2C), 145.02 (8C), 144.83, 144.52 (2C), 144.25, 144.05, 143.38,
141.91 (2C), 141.43, 141.08, 140.90, 140.70, 138.98, 135.15, 71.30 (1C), 69.62 (2C,
3
-1
sp -C of C ), 67.46 (2C), 57.81 (1C), 53.36 (1C); FT-IR ν/cm (KBr) 2920, 1510,
6
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1428, 1383, 1341, 1182, 1117, 770, 670, 573, 527; UV-vis (CHCl ) λmax/nm 256, 306,
3
−
4
31; HRMS (MALDI-TOF) m/z: [M] Calcd for C H NO 821.0841; Found
6
5
11
8
21.0841.
Fulleropyrrolidine 4j: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 3j
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
6
0
o
(124 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 15 min afforded first unreacted
6
f
C (23.3 mg, 65%) and then 4j (8.6 mg, 21%, R = 0.4) as amorphous brown solid
6
0
f
with CS as the eluent: mp > 300 °C.
2
Fulleropyrrolidine 4k: According to the general synthetic procedure, the reaction
of C (36.0 mg, 0.05 mmol) with paraformaldehyde (22.5 mg, 0.75 mmol) and 3k
6
0
o
(237 μL, 1.25 mmol) in ODCB (6 mL) at 180 C for 15 min afforded first unreacted
C (14.9 mg, 41%) and then 4k (24.9 mg, 53%, R = 0.55) as amorphous brown solid
6
0
f
1
with CS as the eluent): mp > 300 °C. 4k: H NMR (500 MHz, CS /DMSO-d ) δ 7.41
2
2
6
(d, J = 7.5 Hz, 4H), 7.27 (t, J = 7.5 Hz, 4H), 7.15 (t, J = 7.3 Hz, 2H), 4.56 (t, J = 7.5
Hz, 1H), 4.39 (s, 4H), 3.71 (d, J = 7.5 Hz, 2H); 13C{ H} NMR (125 MHz,
CS /DMSO-d ) (all 4C unless indicated) δ 153.82, 145.96 (2C), 144.95, 144.91,
1
2
6
1
1
44.76, 144.42 (2C), 144.15, 143.98, 143.30, 142.13 (2C, aryl C), 141.81 (2C),
41.35, 140.99, 140.82, 140.61, 138.87, 135.02, 127.51 (aryl C), 127.40 (aryl C),
3
125.58 (2C, aryl C), 69.48 (2C, sp -C of C ), 66.63 (2C), 58.12 (1C), 49.43 (1C);
6
0
-1
FT-IR ν/cm (KBr) 2964, 2847, 1507, 1463, 1450, 1426, 1345, 1184, 1118, 1029,
893, 753, 736, 696, 574, 527; UV-vis (CHCl ) λmax/nm 257, 306, 431; HRMS
3
−
(
MALDI-TOF) m/z: [M] Calcd for C H N 943.1361; Found 943.1361.
7
6
17
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