A general method for the synthesis of 2,2-[60]fullerenoalkanals: The reaction of [60]fullerene with 2-bromoenol silyl ethers

Article abstract of DOI:10.1055/s-0030-1258112

Five kinds of 2,2-[60]fullerenoalkanals were synthesized by the fluoride ion-mediated reaction of [60]fullerene with 2-bromoenol silyl ethers, which were easily prepared by 2-bromination of the corresponding enol silyl ethers. The reactivity differed significantly depending on the stability of the 2-bromoenol silyl ethers. High yield and selectivity were achieved for the reaction of 2-bromoenol trimethylsilyl ethers under mild conditions (KF/18-crown-6-ether). The reaction of stable 2-bromoenol tert-butyldimethylsilyl ethers, on the other hand, required the use of more reactive tetrabutylammonium fluoride as a fluoride ion source. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-0030-1258112

LETTER
1811
A General Method for the Synthesis of 2,2-[60]Fullerenoalkanals:
The Reaction of [60]Fullerene with 2-Bromoenol Silyl Ethers
S
ynthesis of 2,2-[
6
i
0]Fulle
r
renoalk
o
nals shi Ito, Yusuke Kishi, Yohei Nishikawa, Tomonori Tada, Yasuhiro Ishida, Kazuhiko Saigo*,1
Department of Chemistry and Biotechnology, Graduated School of Engineering, The University of Tokyo,
Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
Fax +81(887)572520; E-mail: saigo.kazuhiko@kochi-tech.ac.jp
Received 22 February 2010
very high reactivity in the reaction. On the basis of these
results, we considered that 2,2-[60]fullerenoalkanals
could be directly synthesized by the reaction of
[60]fullerene with alkanal-derived 2-halogenated enol
Abstract: Five kinds of 2,2-[60]fullerenoalkanals were synthesized
by the fluoride ion-mediated reaction of [60]fullerene with 2-bro-
moenol silyl ethers, which were easily prepared by 2-bromination
of the corresponding enol silyl ethers. The reactivity differed signif-
icantly depending on the stability of the 2-bromoenol silyl ethers. silyl ethers. Herein, we report details of the synthesis of
High yield and selectivity were achieved for the reaction of 2-bro-
2,2-[60]-fullerenoalkanals by the enol silyl ether (ESE)
moenol trimethylsilyl ethers under mild conditions (KF/18-crown-
method.
6-ether). The reaction of stable 2-bromoenol tert-butyldimethylsilyl
ethers, on the other hand, required the use of more reactive tetra-
butylammonium fluoride as a fluoride ion source.
O
O
Cl
R
Ph
Key words: fullerenes, cyclopropanation, silyl enol ethers, alde-
hydes, bromine
R
C60
+
Ph
+ F–
R
OTMS
Ph
– Cl–
– TMSF
Cl
The introduction of a reactive functional group on a
fullerene surface enables the construction of sophisticated
fullerene-based functionalized molecules by functional
group transformations.2–4 Considering the high impor-
tance of a formyl group in organic synthesis, 2,2-
(R = H, Me)
Scheme 1 Synthesis of 2,2-[60]fullerenoalkanones by the ESE me-
thod
[60]fullerenoalkanals
(formylmethano[60]fullerenes),
which have a formyl group at the bridgehead carbon of
methano[60]fullerenes, would be a class of fundamental
importance in fullerene chemistry. We have recently
reported the synthesis5 and application6 of 2,2-
The preparation of 2-brominated enol silyl ethers (2-
BrESEs) is summarized in Scheme 2. Among several
methods available for the synthesis of 2-halogenated
ESEs reported so far, the most convenient method was the
one-pot reaction of enol silyl ethers with bromine fol-
lowed by the elimination of hydrogen bromide by triethy-
lamine to afford 2-BrESEs, because of the accessibility
from commercially available starting materials.9 Accord-
ing to this method, we synthesized several kinds of
2-BrESEs 1a–e from enol trimethylsilyl ethers.10 The
2-BrESEs 1a–e were purified by distillation to afford E/Z
mixtures in moderate yields; the E/Z ratios were 10:90 to
5:>95 (by 1H NMR). The 2-bromoenol tert-butyldimeth-
ylsilyl ethers 1c¢ and 1d¢ were synthesized in a similar
manner.11,12 The compounds 1c¢ and 2d¢ were relatively
stable compared to 1c and 1d and could be purified by
silica-gel column chromatography, although the yields
were rather low.
[60]fullerenoalkanals;
the
cyclopropanation
of
[60]fullerene with a-formyl sulfonium ylides was found
to be a fascinating method for the synthesis of 2,2-
[60]fullerenoalkanals. However, this sulfonium ylide
method has a fatal flaw: 2,2-[60]fullerenoalkanals even
with simple groups, such as a benzyl group, at the bridge-
head carbon could not be synthesized by this method,5 al-
though the reason is not clear at present. Moreover, Wang
et al. have recently reported the synthesis of 2,2-
[60]fullerenoalkanals through the rearrangement of
[60]fullerene-fused tetrahydrofurans bearing an acetal
moiety by BF3 at 110 °C.7 This rearrangement method en-
ables the introduction of many kinds of substituents, in-
cluding sterically large groups, at the bridgehead carbon.
On the other hand, we have reported the synthesis of 2,2-
[60]fullereno-1-phenylalkanones by the fluoride ion-
mediated cyclopropanation of [60]fullerene with 2-halo-
genated 1-phenyl-1-alkenyl trimethylsilyl ethers
(Scheme 1); 8 the 2-halogenated enol silyl ethers showed
The 2-BrESEs were applied to the cyclopropanation of
[60]fullerene (Scheme 3, Table 1).13 At first, the reaction
conditions were optimized by using 1a. When tetrabutyl-
ammonium fluoride (TBAF; 1 M solution in THF) was
used as a fluoride ion source, the reactions took place
smoothly (entries 1 and 2); the reaction of [60]fullerene
with three equivalents of 1a and TBAF afforded the de-
sired 2,2-[60]fullerenoalkanal 2a in moderate yield with
acceptable selectivity14 that was comparable to those ob-
SYNLETT 2010, No. 12, pp 1811–1814
x
x
.x
x
.2
0
1
0
Advanced online publication: 30.06.2010
DOI: 10.1055/s-0030-1258112; Art ID: U01110ST
© Georg Thieme Verlag Stuttgart · New York

1812
H. Ito et al.
LETTER
OTMS
OTMS
H
O
i)
R
R
R
H
H
H
Br
R
OSi
4a: R = Et
1a 70%
1b 57%
1c 88%
1d 13%
1e 56%
C60, F–
toluene, r.t.
4b: R = n-C10H21
4c: R = Bn
4d: R = Ph
4e: R = H
Br
H
1a–e (Si = TMS)
1c',d' (Si = TBDMS)
2a–e
O
OTBDMS
H
OTBDMS
H
ii)
i)
Scheme 3 Synthesis of 2,2-[60]fullerenoalkanals 2a–e. F–: TBAF
(1.0 M solution in THF) or KF/18-crown-6.
R
R
R
H
H
Br
3c: R = Bn
3d: R = Ph
4c' 45%
4d' 51%
1c' 13%
1d' 6%
TBAF as the fluoride ion source in the present reaction. A
further improvement in selectivity without lowering the
yield was achieved by decreasing the amount of 18-
crown-6-ether; the reaction of [60]fullerene with one
equivalent of 1a in the presence of one equivalent of KF
and 0.2 equivalents of 18-crown-6-ether, resulted in good
yield with high selectivity (entry 6).
Scheme 2 Synthesis of the 2-bromoenol silyl ethers 1a–e, 1c¢ and
1d¢. Reagents and conditions: (i) Br2 (1.0 equiv), Et3N (1.5 equiv),
CH2Cl2, –78 °C to r.t., 3 h; (ii) TBDMSOTf (1.25 equiv), Et3N (2.5
equiv), THF, 0 °C to r.t.
tained by the sulfonium ylide method. When an equimolar
amount of KF/18-crown-6 was used as a fluoride ion
source, on the other hand, higher yields and selectivities
were achieved, although a considerably prolonged reac-
tion time was required to complete the reaction (entry 3).
Thus, KF/18-crown-6 was found to be more suitable than
We next carried out the synthesis of several kinds of 2,2-
[60]fullerenoalkanals under the optimized reaction condi-
tions (entries 7–14). All of the 2,2-[60]fullerenoalkanals
2b–e were obtained in moderate yields by the reaction of
[60]fullerene with the 2-BrESEs 1b–e. It is noteworthy
Table 1 Synthesis of the 2,2-[60]Fullerenoalkanals 2a–e
Entry
1
SEE (equiv)
1a (1.0)
1a (3.0)
1a (1.0)
1a (3.0)
1a (1.0)
1a (1.0)
1b (1.0)
1b (3.0)
1c (1.0)
1c (1.0)
1d (1.0)
1d (1.0)
1e (1.0)
1e (1.0)
1c¢ (1.0)
1c¢ (1.5)
1d¢ (1.0)
1d¢ (1.0)
1d¢ (1.5)
F– (equiv)
Time (h)
3
Yield (%)
20
Selectivity (%)a
TBAF (1.0)
39
45
71
30
97
85
95
69
>99
79
94
87
>99
>99
–
2
TBAF (3.0)
3
37
3
KF (1.0), 18-crown-6 (1.0)
KF (3.0), 18-crown-6 (3.0)
KF (1.0), 18-crown-6 (0.2)
KF (1.0), 18-crown-6 (0.2)
KF (1.0), 18-crown-6 (0.2)
KF (3.0), 18-crown-6 (0.2)
KF (1.0), 18-crown-6 (0.2)
KF (1.0), 18-crown-6 (0.2)
KF (1.0), 18-crown-6 (0.2)
KF (1.0), 18-crown-6 (0.2)
KF (1.0), 18-crown-6 (0.2)
KF (1.0), 18-crown-6 (0.2)
KF (1.0), 18-crown-6 (0.2)
TBAF (1.5)
24
24
42
72
42
42
42
72
24
42
42
48
72
3
47
4
26
5
38
6
47
7
19
8
45
9
24
10
11
12
13
14
15
16
17
18
19
54
51
54
2
17
N.D.b
37
49
–
KF (1.0), 18-crown-6 (0.2)
TBAF (1.0)
72
3
N.D.b
30
47
48
TBAF (1.5)
3
33
a Yield based on consumed [60]fullerene.
b Not detected.
Synlett 2010, No. 12, 1811–1814 © Thieme Stuttgart · New York

LETTER
Synthesis of 2,2-[60]Fullerenoalkanals
1813
that it was possible to introduce a benzyl group at the
bridgehead carbon of a 2,2-[60]fullerenoalkanal, which
was impossible by using the sulfonium ylide method.
References and Notes
(1) Present address: School of Environmental Science and
Technology, Koch University of Technology, Miyanokuchi,
Tosayamada-cho, Kami-shi, Kochi 782-8502, Japan
(2) (a) Guldi, D.; Martin, N. Fullerenes: From Synthesis to
Optoelectronic Properties, 1st ed.; Springer: Berlin, 2002.
(b) Hirsch, A.; Brettreich, M. Fullerenes: Chemistry and
Reactions, 1st ed.; Wiley-VCH: Weinheim, 2005.
(3) (a) Wudl, F. Acc. Chem. Res. 1992, 25, 157. (b) Bingel, C.
Chem. Ber. 1993, 126, 1957. (c) Maggini, M.; Scorrano, G.;
Prato, M. J. Am. Chem. Soc. 1993, 115, 9798.
The 2-BrESEs 1c¢ and 1d¢, on the other hand, required sur-
prisingly long reaction times when KF/18-crown-6 was
used as the fluoride ion source (entries 15 and 17). In con-
trast, when TBAF was applied as a fluoride ion source, the
yields reached almost maximum values within a few
hours after the addition of TBAF, to afford 2c and 2d in
moderate yields with acceptable selectivities (entries 16,
18, and 19).
(d) Ganapathi, P. S.; Rubin, Y. J. Org. Chem. 1995, 60,
2954. (e) Sawamura M., Iikura H., Nakamura E.; J. Am.
Chem. Soc.; 1996, 118: 12850.
These results would indicate that the slow generation of
enolates by the reaction of the 2-BrESEs with fluoride
ions is essential because [60]fullerene and the enolates
have highly electron-accepting and electron-donating
properties, respectively. As a result, an electron transfer
from the enolates to [60]fullerene takes place easily to
cause the formation of unidentified by-products (low se-
lectivity). In the case of the enol trimethylsilyl ethers 1a–
e, the fluoride ion would be able to easily attack the silicon
atom to generate the corresponding enolates in a very
short reaction time; the reaction using 0.2 equivalents of
18-crown-6 (entry 6) gave a better result than that using
1.0 equivalent of the crown ether (entry 3) and even that
using TBAF (entry 2), although the reaction required a
more prolonged reaction time. In contrast, in the case of
the enol tert-butyldimethylsilyl ethers 1c¢ and 1d¢, the at-
tack of a fluoride ion on the silicon atom becomes very
slow due to the steric congestion caused by the tert-butyl
and dimethyl groups on the silicon atom. Therefore, the
reaction of [60]fullerene would require fluoride ions in a
concentration that is clearly higher than those generated
from 1.0 equivalents of KF and 0.2 equivalents of the
crown ether.
(4) For selected examples of recent methods for the preparation
of functionalized [60]fullerenes, see: (a) Chen, Z.;Wang, G.
J. Org. Chem. 2005, 70, 2380. (b) Wang, G.; Li, F.; Zhang,
T. Org. Lett. 2006, 8, 1355. (c) Li, F.; Liu, T.; Wang, G.
J. Org. Chem. 2008, 73, 6417. (d) Tzirakis, M. D.;
Orfanopoulos, M. J. Am. Chem. Soc. 2009, 131, 4063.
(5) Hamada, M.; Hino, T.; Kinbara, K.; Saigo, K. Tetrahedron
Lett. 2001, 42, 5069.
(6) (a) Ito, H.; Ishida, Y.; Saigo, K. Tetrahedron Lett. 2005, 46,
8757. (b) Ito, H.; Ishida, Y.; Saigo, K. Tetrahedron Lett.
2006, 47, 3095. (c) Ito, H.; Ishida, Y.; Saigo, K. J. Org.
Chem. 2006, 71, 4759.
(7) Wang, G.; Lu, Y.; Chen, Z.; Wu, S. J. Org. Chem. 2009, 74,
4841.
(8) Hino, T.; Kinbara, K.; Saigo, K. Tetrahedron Lett. 2001, 42,
5065.
(9) Zembayashi, M.; Tamao, K.; Kumada, M. Synthesis 1977,
422.
(10) General procedure for the synthesis 2-bromoenol trimethyl-
silyl ethers 1a–e. Bromine (1.9 mL, 37 mmol) and triethyl-
amine (7.7 mL, 55 mmol) were successively added dropwise
to a solution of 1-trimethylsiloxy-1-alkene (37 mmol) in
CH2Cl2 (28 mL) at –78 °C, and the mixture was stirred at r.t.
for 3 h. Then, hexane (30 mL) was added to the mixture, and
the resultant white precipitates were filtered off. The filtrate
was washed with saturated NaHCO3 (100 mL), H2O (100
mL) and brine (100 mL), successively. The organic layer
was dried over sodium sulfonate and filtered, and the solvent
was removed under reduced pressure. The residue was
purified by distillation under reduced pressure to afford the
corresponding 2-BrESE (E/Z mixture) as a clear liquid.
2-Bromo-1-trimethylsiloxy-1-butene (1a): Ratio major/
minor = 89:11 (determined by 1H NMR). Bp 63–73 °C/15
mmHg. IR (neat): 2969, 2937, 2917, 2876, 2804, 1656,
1457, 1336, 1317, 1255, 1191, 1129, 1106, 1068, 1041, 942,
924, 867, 846, 754 cm–1. 1H NMR (300 MHz, CDCl3):
d (major) = 6.47 (t, J = 0.6 Hz, 1 H), 2.5–2.4 (m, 2 H), 1.1–
1.0 (m, 3 H), 0.3–0.2 (m, 9 H); d (minor) = 6.15 (t, J = 0.6
Hz, 1 H), 2.5–2.4 (m, 2 H), 1.1–1.0 (m, 3 H), 0.3–0.2 (m,
9 H). 13C NMR (75 MHz, CDCl3): d = 135.28, 111.51,
29.24, 14.38, –0.02. MS (EI): m/z (%) = 222 (100), 224
(100).
The 2-bromoenol silyl ethers 1a–e were thermally unsta-
ble, which sometimes resulted in their decomposition dur-
ing distillation. This means that the use of 1a–e without
purification by distillation is desirable. To this end, we
conducted the reaction of [60]fullerene with 1a prepared
in situ. As a typical example, the use of five equivalents of
4a for the one-pot reaction gave 2a in 46% yield.15 Thus,
the reaction of [60]fullerene with 1 prepared in situ was
also found to proceed smoothly.
In conclusion, various types of 2,2-[60]fullerenoalkanals
were directly synthesized by the fluoride ion-mediated cy-
clopropanation of [60]fullerene with 2-brominated ESEs.
This general and reliable reaction for the synthesis of 2,2-
[60]fullerenoalkanals in a few steps should contribute to
the development of new types of [60]fullerene-containing
materials. The transformation of 2,2-[60]fullerenoalkan-
als thus obtained is now in progress.
2-Bromo-1-trimethylsiloxy-1-dodecene (1b): Ratio major/
minor = 92:8 (determined by 1H NMR). Bp ~124 °C/1
mmHg. IR (neat): 2956, 2925, 2854, 1730, 1657, 1465,
1254, 1195, 870, 848, 756 cm–1. 1H NMR (300 MHz,
CDCl3): d (major) = 6.44 (s, 1 H), 2.43 (t, J = 6.9 Hz, 2 H),
1.89 (br, 2 H), 1.26 (br, 16 H), 0.3–0.2 (m, 9 H); d (minor) =
6.50 (s, 1 H), 2.43 (t, J = 6.9 Hz, 2 H), 1.89 (br, 2 H), 1.26
(br, 16 H), 0.3–0.2 (m, 9 H). 13C NMR (75 MHz, CDCl3):
d = 135.84, 35.49, 32.25, 29.94, 29.88, 29.81, 29.67, 29.63,
28.68, 28.56, 23.03, 14.47, –0.02. MS (EI): m/z (%) = 334
(100), 336 (100).
Acknowledgment
This work was supported in part by a Grant-in-Aid for challenging
Exploratory Research (19655039) from the Japan Society for the
Promotion of Science.
Synlett 2010, No. 12, 1811–1814 © Thieme Stuttgart · New York

1814
H. Ito et al.
LETTER
2-Bromo-3-phenyl-1-trimethylsiloxy-1-propene (1c):
Ratio major/minor = 89:11 (determined by 1H NMR). Bp
~112 °C/1.5 mmHg. IR (neat): 3029, 2958, 2900, 1731,
1659, 1603, 1495, 1454, 1419, 1333, 1254, 1210, 1172, 868,
849, 748, 698 cm–1. 1H NMR (300 MHz, CDCl3): d (major)
= 7.3–7.2 (m, 5 H), 6.59 (t, J = 0.9 Hz, 1 H), 3.64 (s, 2 H),
0.3–0.2 (m, 9 H); d (minor) = 7.3–7.2 (m, 5 H), 6.64 (t,
J = 0.9 Hz, 1 H), 3.80 (s, 2 H), 0.3–0.2 (m, 9 H). 13C NMR
(75 Hz, CDCl3): d = 138.31, 137.19, 128.62, 128.36, 126.63,
107.44, 41.49, –0.34. MS (EI): m/z (%) = 284 (100), 226
(100).
2-Bromo-2-phenyl-1-(trimethylsiloxy)ethene (1d): Ratio
major/minor = 90:10 (determined by 1H NMR). Bp ~78 °C/
1 mmHg. IR (neat): 3060, 3031, 2958, 1727, 1636, 1491,
1443, 1255, 1167, 935, 758, 694 cm–1. 1H NMR (300 MHz,
CDCl3): d (major) = 7.5–7.2 (m, 4 H), 6.96 (s, 1 H), 0.30 (s,
9 H); d (minor) = 6.50, 7.5–7.2 (m, 4 H), 6.90 (s, 1 H), 0.24
(s, 9 H). 13C NMR (75 MHz, CDCl3): d = 138.50, 129.25,
129.04, 128.32, 127.62, 127.37, –0.27. MS (EI): m/z
(%) = 270 (100), 272 (100).
(EI): m/z (%) = 312(100), 314(100). Minor isomer: IR(neat):
2955, 2929, 2858, 1617, 1259, 1228, 1136, 827 cm–1. 1H
NMR (300 MHz, CDCl3): d = 7.8–7.7 (m, 2 H), 7.4–7.1 (m,
3 H), 6.91 (s, 1 H), 0.91 (s, 9 H), 0.19 (s, 6 H). 13C NMR (75
MHz, CDCl3): d = 140.24, 135.50, 128.99, 127.74, 127.31,
106.93, 25.44, 18.07, –5.30. MS (EI): m/z (%) = 312 (100),
314 (100)
(13) General procedure for the synthesis of 2,2-[60]fullereno-
alkanals. The KF/18-crown-6 method: KF (5.8 mg, 0.10
mmol) and an 18-crown-6 solution in toluene (0.10 M, 0.20
mL, 0.020 mmol) were added to a solution of [60]fullerene
(72 mg, 0.10 mmol) and 2-BrESE (0.10 mmol) in toluene
(72 mL). After the mixture was stirred at r.t. for 72 h, the
solvent was evaporated to dryness. The residue was purified
by preparative thin layer chromatography (SiO2, CS2) to
afford the corresponding 2,2-[60]fullerenoalkanal as a dark-
brown solid.
The TBAF method: A TBAF solution (1 M in THF, 0.30
mL, 0.30 mmol) was added to a solution of [60]fullerene (72
mg, 0.10 mmol) and 2-BrESE (0.10 mmol) in toluene (72
mL). After the mixture was stirred at r.t. for 3 h, the solvent
was evaporated to dryness. The residue was purified by
column chromatography [SiO2; hexane–toluene, 9:1 to 2:1
(v/v)] to afford the corresponding 2,2-[60]fullerenoalkanal
as a dark-brown solid.
2-Bromo-1-trimethylsiloxyethene (1e): Bp ~74 °C/52
mmHg. IR (neat): 3106, 3010, 2960, 2901, 1636, 1329,
1255, 1241, 1166, 1094, 878, 849, 757, 708, 655, 605 cm–1.
1H NMR (300 MHz, CDCl3): d = 6.73 (d, J = 3.9 Hz, 1 H),
5.24 (d, J = 3.9 Hz, 1 H), 0.24 (s, 9 H). 13C NMR (75 MHz,
CDCl3): d = 141.41, 87.37, –0.43. MS (EI): m/z (%) = 194
(100), 196 (100)
2,2-[60]Fullerenobutanal (2a): See ref. 5.
2,2-[60]Fullerenododecanal (2b): IR (KBr): 2921, 2849,
1719, 1461, 1428, 1186, 578, 555, 526 cm–1. 1H NMR (300
MHz, CDCl3): d = 10.57 (s, 1 H), 2.79 (t, J = 8.1 Hz, 2 H),
2.02–1.85 (m, 2 H), 1.66–1.18 (m, 14 H), 0.89 (t, J = 6.6 Hz,
3 H). 13C NMR [125 MHz, CDCl3/CS2, 1:1 (v/v)]: d =
194.24, 146.84, 145.79, 145.26, 145.25, 145.23, 145.16,
145.13, 144.97, 144.70, 144.64, 144.62, 144.60, 144.40,
143.76, 143.69, 143.19, 143.08, 143.01, 142.94, 142.92,
142.91, 142.05, 141.98, 141.97, 141.57, 141.10, 141.04,
137.96, 137.83, 75.17, 50.23, 31.99, 30.05, 29.71, 29.69,
29.55, 29.46, 27.70, 25.87, 22.84, 14.23. MS (MALDI-
TOF): m/z [M]·+ calcd for C72H22O: 902.17; found: 902.11.
2,2-[60]Fullereno-3-phenylpropanal (2c): IR (KBr): 2922,
2850, 1718, 1494, 1427, 1260, 1186, 1073, 1030, 732, 706,
576, 555, 526 cm–1. 1H NMR (300 MHz, CDCl3): d = 10.55
(s, 1 H), 7.58 (d, J = 7.4 Hz, 2 H), 7.38 (dd, J = 7.4, 7.4 Hz,
2 H), 7.30 (d, J = 7.4 Hz, 1 H), 4.23 (s, 2 H). 13C NMR [125
MHz, CDCl3/CS2, 1:1 (v/v)]: d = 193.83, 146.85, 145.61,
145.38, 145.35, 145.28, 145.27, 144.98, 144.82, 144.81,
144.80, 144.78, 144.76, 144.58, 143.88, 143.78, 143.20,
143.18, 143.06, 143.01, 142.17, 142.10, 142.07, 141.62,
141.24, 138.15, 138.12, 136.77, 129.40, 128.95, 127.25,
74.98, 50.15, 31.56; three peaks are overlapped. MS
(MALDI-TOF): m/z [M]·+ calcd for C69H8O: 852.06; found:
851.80.
(11) The enol tert-butyldimethylsilyl ethers 4c¢ and 4d¢ were
synthesized according to a method in the literature,16 and
was purified by silica gel column chromatography.
1-tert-Butyldimethylsilyloxy-3-phenylpropene (4c¢):
IR(neat): 3029, 2955, 2929, 2858, 1655, 1255, 1115, 838
cm–1. 1H NMR (300 MHz, CDCl3): d = 7.4–7.1 (m, 5 H),
6.30 (dt, J = 5.7, 1.5 Hz, 1 H), 4.67 (dt, J = 5.7, 7.2 Hz, 1 H),
3.45 (dd, J = 1.5, 7.2 Hz, 2 H), 0.94 (s, 9 H), 0.15 (s, 6 H).
13C NMR (75 MHz, CDCl3): d = 141.97, 139.10, 128.32,
128.25, 125.58, 109.08, 29.92, 25.63, 18.26, –5.33. MS (EI):
m/z = 248.
1-tert-Butyldimethylsilyloxy-2-phenylethene (4d¢): Ratio
major/minor = 52:48 (determined by 1H NMR). IR (neat):
3030, 2955, 2930, 2885, 2858, 1645, 1471, 889, 838, 783,
692 cm–1. 1H NMR (300 MHz, CDCl3): d (major) = 7.3–7.1
(m, 5 H), 7.00 (d, J = 12.3 Hz, 1 H), 6.03 (d, J = 12.3 Hz,
1 H), 0.96 (s, 9 H), 0.21 (s, 6 H); d (minor) = 7.7–7.6 (m,
2 H), 7.3–7.1 (m, 3 H), 6.42 (d, J = 6.6 Hz, 1 H), 5.30 (d,
J = 6.6 Hz, 1 H), 0.98 (s, 9 H), 0.22 (s, 6 H). 13C NMR (75
MHz, CDCl3): d = 142.23, 140.51, 136.47, 136.19, 128.49,
128.18, 128.07, 125.73, 125.63, 125.12, 112.82, 108.84,
25.68, 25.62, 18.32, 18.21, –5.18, –5.38. MS (EI): m/z = 234
(12) The 2-bromoenol tert-butyldimethylsilyl ethers 1c¢ and 1d¢
were synthesized in a similar manner to that used for the
preparation of the 2-boromoenol trimethylsilyl ethers. The
crude products were purified by column chromatography
[SiO2; hexane–CH2Cl2, 10:0 to 8:2 (v/v)].
2,2-[60]Fullereno-2-phenylethanal (2d): See ref. 7.
2,2-[60]Fullerenoethanal (2e): See ref. 7.
(14) [60]Fullerene derivatives having two or more alkanal
moieties were obtained as by-products.
2-Bromo-1-tert-butyldimethylsilyloxy-3-phenylpropene
(1c¢): IR(neat): 3029, 2954, 2929, 2858, 1659, 1254, 1211,
1171, 838 cm–1. 1H NMR (300 MHz, CDCl3): d = 7.4–7.2
(m, 5 H), 6.61 (s, 1 H), 3.64 (s, 2 H), 0.96 (s, 1 H), 0.19 (s,
1 H). 13C NMR (75 MHz, CDCl3): d = 138.38, 137.72,
128.63, 128.34, 126.61, 106.92, 441.42, 25.51, 18.27, –5.17.
MS (EI): m/z (%) = 326 (100), 328 (100).
2-Bromo-1-tert-butyldimethylsilyloxy-2-phenylethene
(1d¢): Ratio major/minor = 65:35 (determined by 1H NMR).
Major isomer: IR (neat): 2954, 2929, 2858, 1635, 1261,
1168, 828 cm–1. 1H NMR (300 MHz, CDCl3): d = 7.5–7.4
(m, 2 H), 7.4–7.2 (m, 3 H), 6.98 (s, 1 H), 0.99 (s, 1 H), 0.24
(s, 1 H). 13C NMR (75 MHz, CDCl3): d = 138.91, 137.11,
128.31, 127.53, 127.32, 106.74, 25.50, 18.26, –5.11. MS
(15) Br2 (0.40 M in CH2Cl2, 1.25 mL, 0.50 mmol) and Et3N (1.5
M in CH2Cl2, 0.50 mL, 0.75 mmol) were successively added
dropwise to a solution of 1-trimethylsilyloxy-1-butene (4a;
72 mg, 0.50 mmol) in CH2Cl2 (7.5 mL) at –78 °C, and the
mixture was stirred at r.t. for 3 h. A solution of [60]fullerene
(0.10 mM in toluene, 72 mL), KF (29 mg, 0.50 mmol), and
18-crown-6 (26 mg, 0.10 mmol) were successively added to
the mixture. After the mixture was stirred at r.t. for 42 h, the
solvent was evaporated to dryness. The residue was purified
by preparative thin layer chromatography (SiO2, CS2) to
afford 2,2-[60]fullerenobutanal 1a (36 mg, 0.46 mmol, 46%
yield) as a dark-brown solid
(16) Jung, M. E.; Nishimura, N. Org. Lett. 2001, 3, 2113.
Synlett 2010, No. 12, 1811–1814 © Thieme Stuttgart · New York

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