An alternative type of fullerene products from the reaction of [60]fullerene with alkoxides and subsequent derivatization

Article abstract of DOI:10.1021/jo9005848

(Chemical Equation Presented) Reaction of [60]fullerene with freshly prepared RCH₂CH₂ONa/RCH₂CH₂OH (R ) H, Me, Et, Ph) in anhydrous toluene in the presence of air unexpectedly afforded fullerene products with a

Full text of DOI:10.1021/jo9005848

An Alternative Type of Fullerene Products from the Reaction of
[60]Fullerene with Alkoxides and Subsequent Derivatization
Guan-Wu Wang,*,†,‡ Yong-Ming Lu,† Zhong-Xiu Chen,† and Shi-Hui Wu§
Hefei National Laboratory for Physical Sciences at Microscale and Department of Chemistry, UniVersity
of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China, State Key
Laboratory of Applied Organic Chemistry, Lanzhou UniVersity, Lanzhou,
Gansu 730000, People’s Republic of China, and Department of Chemistry, Fudan UniVersity,
Shanghai 200433, People’s Republic of China
gwang@ustc.edu.cn
ReceiVed March 17, 2009
Reaction of [60]fullerene with freshly prepared RCH2CH2ONa/RCH2CH2OH (R ) H, Me, Et, Ph) in
anhydrous toluene in the presence of air unexpectedly afforded fullerene products with a C60-fused
tetrahydrofuran ring skeleton and an acetal moiety, which could be further transformed into C60-fused
dihydrofurans, tolyl-substituted C60-fused tetrahydrofuran, and methanofullerenes bearing a formyl group
by boron trifluoride etherate. Possible reaction mechanisms are proposed to explain the formation of
different fullerene products.
Introduction
groups determined by mass spectroscopy).2 Similar result was
obtained from the reaction of C60Fn with MeONa/MeOH.3
Reaction of C60Cl6 with ArOH/KOH gave benzo[b]furano-
[2,′3′:1,2][60]fullerene derivatives along with other products
arising from substitution/elimination occurring across the 1,2-
positions of the hexachloro precursor and nucleophilic replace-
ment of some of the other chloro addends in the precursor by
arenoxy groups.4 Isolation of pure C60(OR)5Cl was achieved
by the reaction of C60Cl6 with RONa/ROH (R ) Me, Et).5
Various types of reactions to functionalize fullerenes have
been described.1 Among them nucleophilic addition is one of
the first examined reactions. Grignard reagents, organolithium
reagents, and amines have been widely employed to synthesize
fullerene derivatives.1 However, the reaction of [60]fullerene
(C60) with alkoxides has been scarcely investigated. Olah et al.
were the first to treat fullerene derivatives C60Cln with MeOH/
KOH or MeONa/MeOH and observed the formation of a
mixture of polymethoxylated C60(OMe)n (up to 26 methoxy
(2) Olah, G. A.; Bucsi, I.; Lambert, C.; Aniszfeld, R.; Trivedi, N. J.;
Sensharma, D. K.; Prakash, G. K. S. J. Am. Chem. Soc. 1991, 113, 9385.
(3) Taylor, R.; Holloway, J. H.; Hope, E. G.; Avent, A. G.; Langley, G. J.;
Dennis, T. J.; Hare, J. P.; Kroto, H. W.; Walton, D. R. M. J. Chem. Soc., Chem.
Commun. 1992, 665.
(4) Avent, A. G.; Birkett, P. R.; Darwish, A. D.; Houlton, S.; Taylor, R.;
Thomson, K. S. T.; Wei, X.-W. J. Chem. Soc., Perkin Trans. 2 2001, 782.
(5) Darwish, A. D.; Avent, A. G.; Kroto, H. W.; Taylor, R.; Walton, D. R. M.
J. Chem. Soc., Perkin Trans. 2 1999, 1983.
† University of Science and Technology of China.
‡ Lanzhou University.
§ Fudan University.
(1) For reviews, see: (a) Taylor, R.; Walton, D. R. M. Nature 1993, 363,
685. (b) Hirsch, A. Synthesis 1995, 895. (c) Diederich, F.; Thilgen, C. Science
1996, 271, 317. (d) Yurovskaya, M. A.; Trushkov, I. V. Russ. Chem. Bull., Int.
Ed. 2002, 51, 367. (e) Thilgen, C.; Diederich, F. Chem. ReV. 2006, 106, 5049.
10.1021/jo9005848 CCC: $40.75  2009 American Chemical Society
Published on Web 06/08/2009
J. Org. Chem. 2009, 74, 4841–4848 4841

Wang et al.
a similar acetal moiety.10,11 The two CH2O protons were
nonequivalent. One proton as a dq multiplet was located at 4.32
ppm (J ) 9.5, 7.1 Hz), and another proton with the same
splitting pattern was embedded in 3.88-3.99 ppm. In the 13C
NMR spectrum of compound 2, there were 43 peaks with some
overlapping ones in the range of 134-156 ppm for the 58 sp2-
carbons of the fullerene skeleton, consistent with its molecular
structure with C1 symmetry. The two sp3-carbons of the C60
cage were located at 66.71 and 98.41 ppm, while the acetal
carbon appeared at 102.68 ppm. The chemical shifts for the
sp3-carbons of the C60 skeleton connecting the oxygen atom and
the acetal carbon in compound 2 were close to those in
compound 19 and other similar compounds.11 The structure
assignment of product 2 was further confirmed by its HMQC
and HMBC spectra, which clearly demonstrated that the two
nonequivalent protons (∼3.9 and 4.32 ppm) were bound to the
CH2O carbon (63.00 ppm) and that the proton at 6.15 ppm was
connected to the acetal carbon (102.68 ppm) and showed a three-
bond correlation with the sp3-carbon of the C60 skeleton at 98.41
ppm. The UV-vis spectrum of product 2 showed a peak at
427 nm, which is the characteristic peak for a 1,2-adduct of
C60.11
FIGURE 1. Structure of compound 1.
FIGURE 2. Structure of compound 2.
Nucleophilic addition of MeONa/MeOH to fullerene compounds
bearing an epoxy group and/or tert-butylperoxy groups gave
methoxylated derivatives.6 On the other hand, Wilson and Wu
reported that the addition of a MeONa/MeOH solution to C60
-
itself in toluene led to formation of C60(OMe)n (n ) 1, 3, 5,
7) as major anions as well as a product derived from coupling
and oxidation with toluene, C60O2(CH2C6H5)-.7 Nevertheless,
attempts to isolate these products from the reaction mixture were
not successful, and the adducts were only detected by ESI-MS.
The anion C60(OMe)- was also detected by mass and vis-near-
IR spectroscopies from the reaction mixture of C60 and MeO-
in benzonitrile.8 In 1995, we described the preparation of a C60-
fused 1,3-dioxolane derivative 1 (Figure 1) by the reaction of
C60 with PhCH2ONa/PhCH2OH.9 Even though we also con-
ducted the reaction of C60 with EtONa/EtOH and isolated an
adduct, we could not solve the structure of the product at that
time. Herein we report the unexpected structure of the ethoxide-
C60 adduct, and a systematic study on the novel reaction of C60
with other sodium alkoxides and subsequent functionalization
of the obtained fullerene products.
Further investigation revealed that alkoxide/alcohol mixtures
prepared from primary alcohols bearing ꢀ-hydrogen could react
with C60, and afforded fullerene derivatives with a structure
similar to compound 2 rather than compound 1. The reaction
n
n
of C60 with 10 equiv of PrONa/nPrOH, BuONa/nBuOH, and
PhCH2CH2ONa/PhCH2CH2OH in anhydrous toluene in the
presence of air gave products 3, 4, and 5, respectively (Scheme
1).
For products 3-5, there existed two (cis and trans) isomers,
depending on the orientations of the R and RCH2CH2O groups.
These two isomers could be separated by flash column chro-
matography over silica gel with carbon disulfide as the eluent.
The reaction times, product yields, and cis/trans isomeric
ratios along with recovered C60 for the reaction of C60 with 10
equiv of alkoxides at room temperature affording products 2-5
are listed in Table 1. It should be pointed out that the reaction
of C60 with ethoxide gave lower product yield (14%) and less
recovered C60 (9%) compared with the reaction of C60 with other
alkoxide. When the reaction time for the mixture of C60 and
ethoxide was shortened from 3 to 1.5 h, product 2 was obtained
in slightly lower yield (9%) but with much higher recovery of
C60 (62%). These results may hint that ethoxide is more reactive
than other alkoxide. Some unidentified byproducts, which may
contain multiadducts as detected by ESI-MS for the reaction of
C60 with methoxide,7 were observed in the reaction of C60 with
alkoxides.
Results and Discussion
The reaction of C60 with 10 equiv of EtONa/EtOH (freshly
prepared by treating ethanol with sodium) in anhydrous toluene
under aerobic conditions for 3 h afforded an ethoxide-C60 adduct,
which was not a C60-fused 1,3-dioxolane derivative with a
structure similar to compound 1 but instead turned out to be a
fullerene product containing a C60-fused tetrahydrofuran ring
skeleton and an acetal moiety, i.e., compound 2 (Figure 2).
The identity of compound 2 was fully established by its
1
HRMS, H NMR, 13C NMR, HMQC, HMBC, UV-vis, and
IR spectra. The HRMS (ESI) of product 2 gave a peak at
831.0416 for C64H8NaO2+, corresponding to the [M + Na]+
ionic peak. In its 1H NMR spectrum, the acetal proton appeared
as a double doublet at 6.15 ppm, split by the adjacent methylene
protons. The observed small coupling constants (J ) 3.3, 1.2
Hz) have precedents in tetrahydrofuran derivatives containing
Products cis-3, trans-3, cis-4, trans-4, cis-5, and trans-5 were
1
fully characterized by HRMS, H NMR, 13C NMR, UV-vis,
and IR spectra. It is noteworthy that in the 1H NMR spectra of
the cis and trans isomers of products 3-5, the coupling
constants 3JHH between the adjacent methine protons were small
(∼4 Hz) for the cis isomers and diminished to zero for the trans
isomers.10,11 The assignments for the cis and trans isomers were
further confirmed by the calculated coupling constants by
modified Karplus equation. For example, the calculated coupling
constants for the cis and trans isomers of 3 were 6.5 and 2.5
(6) Huang, S.; Xiao, Z.; Wang, F.; Gan, L.; Zhang, X.; Hu, X.; Zhang, S.;
Lu, M.; Pan, Q.; Xu, L. J. Org. Chem. 2004, 69, 2442.
(7) Wilson, S. R.; Wu, Y. J. Am. Chem. Soc. 1993, 115, 10334.
(8) Fukuzumi, S.; Nakanishi, I.; Maruta, J.; Yorisue, T.; Suenobu, T.; Itoh,
S.; Arakawa, R.; Kadish, K. M. J. Am. Chem. Soc. 1998, 120, 6673.
(9) Wang, G.-W.; Shu, L.-H.; Wu, S.-H.; Wu, H.-M.; Lao, X.-F. J. Chem.
Soc., Chem. Commun. 1995, 1071.
(10) Coles, B. F.; Smith, J. R. L. J. Chem. Soc., Perkin Trans. 1979, 1, 2664.
(11) (a) Wang, G.-W.; Li, F.-B.; Xu, Y. J. Org. Chem. 2007, 72, 4774. (b)
Wang, G.-W.; Li, F.-B.; Chen, Z.-X.; Wu, P.; Cheng, B.; Xu, Y. J. Org. Chem.
2007, 72, 4779.
(12) The HLA (4 substituents) equation as modified Karplus equation
implemented in the free available MestReJ program was employed to calculate
coupling constants. The input dihedral angels of 19.5° and 114.6° for cis-3 and
trans-3, respectively, were obtained from the AM1-optimized structures.
4842 J. Org. Chem. Vol. 74, No. 13, 2009

AlternatiVe Type of Fullerene Products
SCHEME 1. Reaction of C60 with Alkoxides
SCHEME 2. Reaction of C60 with Alkoxides and Aldehydes
TABLE 1. Reaction Times, Yields, cis/trans Ratios, and Recovered
C60 for the Reaction of C60 with Alkoxides
TABLE 2. Reaction Times, Yields, cis/trans Ratios, and Recovered
C60 for the Reaction of C60 with Alkoxides and Aldehydes
reaction
time (h)
cis/trans
ratio
recovered
C60 (%)
reaction
time (h)
recovered
C60 (%)
product
yield (%)a
product
yield (%)a
cis/trans
2
3
4
5
3
3
3
6
14
40
22
20
9
39
62
47
2b
3
4
0.5
2
2
22
43
28
25
63
52
47
38
21/19
16/6
9/11
25/18
20/8
12/13
5
6
a Total yield for the cis and trans isomers of 3, 4, and 5.
a Total yield for the cis and trans isomers of 3, 4, and 5. b Excess
gaseous acetaldehyde was slowly bubbled into the reaction mixture of
C60 and EtONa/EtOH.
Hz (∆ ) 4.0 Hz),12 which correlate well with their observed
3.9 and 0.0 Hz (∆ ) 3.9 Hz), respectively. In the 13C NMR
spectra of products 3-5, the two sp3-carbons of C60 skeletons
and the acetal carbon were located at 70.96-73.35, 98.09-99.41,
and 104.04-109.78 ppm, respectively. These data were close
to those in compound 2 and other similar compounds.11
Furthermore, the 13C NMR chemical shifts of the acetal carbons
in the cis isomers (104.04-105.51 ppm) were shifted upfield
about 4-5 ppm relative to those in the trans isomers
(107.90-109.78 ppm). The same phenomenon has been ob-
served previously by us.11b
We found that even though the alkoxide/alcohol mixtures
prepared from 1-propanol and 2-phenylethanol reacted with C60,
those from the isomeric secondary alcohols, i.e., 2-propanol and
1-phenylethanol, failed to react with C60 to give the desired
products. In addition, no corresponding fullerene product could
be isolated from the reaction of C60 with the alkoxide/alcohol
mixture made from a tertiary alcohol such as tert-butanol. These
results implied that alkoxide/alcohol mixtures prepared only
from primary alcohols bearing ꢀ-hydrogen could react with C60
to give fullerene products with a C60-fused tetrahydrofuran ring
skeleton and an acetal moiety.
ratios along with recovered C60 for the reaction of C60 with 10
equiv of alkoxides and 1 equiv of aldehydes at room temperature
affording products 2-5 are listed in Table 2.
It is interesting to observe that reactions of PhCH2ONa/
PhCH2OH and PhCH2CH2ONa/PhCH2CH2OH with C60 gave
different types of products, i.e., adduct 1 and adduct 5,
respectively. It should be also emphasized that only one
molecule of PhCH2O- was incorporated into adduct 1, whereas
apparently two molecules of RCH2CH2O- were integrated into
products 2-5. Obviously, the reaction pathways to generate
product 1 and products 2-5 were completely different. No
reaction occurred when oxygen was excluded from the reaction
mixture of C60 and RCH2CH2ONa/RCH2CH2OH (R ) H, Me,
Et, Ph). Therefore, oxygen played a crucial role in the success
of the above reactions to give products 2-5. Although how
alkoxides RCH2CH2ONa were oxidized to aldehydes RCH2CHO
under our reaction conditions is difficult to know now, their
formation might first involve the electron transfer between C60
7,8
and RCH2CH2O- to give C60 and RCH2CH2O•.
The
-•
R-hydrogen of the alkoxy radical RCH2CH2O• is abstracted by
C60 radical anion or other radical species including another
-•
alkoxyl radical to give aldehydes RCH2CHO,13 as shown in
Scheme 3. The increase in reaction rates and product yields
after purposive addition of aldehydes to the reaction mixtures
of C60 and alkoxides suggested the involvement of aldehydes
in the reactions. One possible mechanism, i.e., path (i) in Scheme
3, for the formation of products 2-5 from the reaction of C60
with alkoxides is the same as that for the reaction of C60 with
aldehydes and alkoxides and had been presented in our previous
report.11b In short, path (i) proceeds through the nucleophilic
attack of the carbanion generated by deprotonation at the
R-carbon of the aldehyde to C60, subsequent oxidation and
addition of the alkoxide to the carbonyl group on the side chain
We recently reported that the reaction of C60 with aldehydes/
ketones and alkoxides gave fullerene products with a skeleton
similar to that of products 2-5.11b We surmised that the same
reaction mechanism might be operated for the reaction of C60
with alkoxides affording products 2-5 if the corresponding
aldehydes could be formed in situ from the RCH2CH2ONa/
RCH2CH2OH mixtures under our experimental conditions. To
our delight, we found that the reaction of C60 with RCH2CH2ONa/
RCH2CH2OH (R ) H, Me, Et, Ph) and the corresponding
aldehyde RCH2CHO (R ) H, Me, Et, Ph) indeed gave products
2-5 (Scheme 2) with nearly the same cis/trans isomeric ratios,
but the reaction was faster and the yield was higher compared
with the reaction of C60 with RCH2CH2ONa/RCH2CH2OH
alone. The reaction times, product yields, cis/trans isomeric
(13) Gray, P.; Williams, A. Chem. ReV. 1959, 59, 239.
J. Org. Chem. Vol. 74, No. 13, 2009 4843

Wang et al.
SCHEME 3. Possible Reaction Mechanism for the
Formation of Products 2-5
SCHEME 4. Conversion of 3-5 to 6-8 Promoted by
BF3 ·Et2O at 50 °C
which undergoes intramolecular cyclization and oxidation to
afford intermediate K. Hydrogen abstraction presumably by
RCH2CH2O• at the methylene moiety next to the oxygen atom
of intermediate K produces radical L, which then couples with
RCH2CH2O• to generate products 2-5. The suggested six steps
giving products 2-5 in path (ii) are similar to the first six steps
affording intermediate K in path (iii). The failure to observe
and isolate intermediate K from the reaction of C60 with
alkoxides at the early stage as well as at the end of reaction
indicates that the reaction of C60 with alkoxides should proceed
through path (i) rather than path (ii) and path (iii). Furthermore,
the stronger nucleophilicity for a carboanion than that for an
oxygen nucleophile such as an alkoxide or hemiacetal anion in
nonprotonic solvents (toluene in the current work) also supports
that the reaction preferably occurs via path (i).
Further transformation of fullerene products gains more and
more attention for the preparation of new fullerene deriva-
tives.1-6,11a,14 Significantly, the challenging synthesis of H2@C60
and H2@C70 was achieved by Komatsu, Murata, and co-workers
who closed the 13-membered ring orifice of the corresponding
hydrogen-encapsulated open-cage fullerenes by four-step organic
reactions.14a-c The Gan group prepared azafullerene derivatives
with peroxide addends by addition of hydroxyl amine to cage-
opened fullerene derivatives, subsequent PCl5-induced rear-
rangement, and final treatment with basic alumina or amines.14d
We therefore investigated the subsequent derivatization of
products 2-5 in order to obtain other valuable fullerene
derivatives.
After extensive screening of the reaction conditions, it was
found that boron trifluoride etherate (BF3 ·Et2O) could efficiently
convert compounds cis-3, trans-3, cis-4, trans-4, cis-5, and
trans-5 to C60-fused dihydrofuran derivatives 6-8 with the
apparent loss of RCH2CH2OH at 50 °C (Scheme 4).
The reaction times and yields for the reaction of both cis
and trans isomers of compounds 3-5 with 100 equiv of
BF3 ·Et2O at 50 °C affording products 6-8 are listed in Table
3. As can be seen from Table 3, the stereochemistry of the
reactants had little influence on the product yields; both cis and
trans isomers gave the identical product in nearly the same
of the formed radical species, and final ring closure via an
intramolecular nucleophilic addition and oxidation.11b Alterna-
tively, the reaction might occur through path (ii) to generate
products 2-5. The hemiacetal intermediate, formed by the
addition of the alkoxide to the corresponding aldehyde, reacts
with C60 to afford fullerenyl anion A. Oxidation of intermediate
A gives fullerenyl radical B, and subsequent intramolecular
hydrogen abstraction and deprotonation generates radical anion
D. Intramolecular cyclization of intermediate D and oxidation
afford the final products 2-5. The third possible mechanism
for the formation of products 2-5 involving alkoxides but no
aldehydes is shown as path (iii) in Scheme 3. Nucleophilic
addition of the alkoxide to C60 followed by oxidation furnishes
fullerenyl radical G. Intramolecular hydrogen abstraction of
radical G and subsequent deprotonation give radical anion I,
(14) For other recent representative examples, see: (a) Komatsu, K.; Murata,
M.; Murata, Y. Science 2005, 307, 238. (b) Murata, M.; Murata, Y.; Komatsu,
K. J. Am. Chem. Soc. 2006, 128, 8024. (c) Murata, M.; Maeda, S.; Morinaka,
Y.; Murata, Y.; Komatsu, K. J. Am. Chem. Soc. 2008, 130, 15800. (d) Zhang,
G.; Huang, S.; Xiao, Z.; Chen, Q.; Gan, L.; Wang, Z. J. Am. Chem. Soc. 2008,
130, 12614. (e) Chen, Z.-X.; Wang, G.-W. J. Org. Chem. 2005, 70, 2380. (f)
Tajima, Y.; Hara, T.; Honma, T.; Matsumoto, S.; Takeuchi, K. Org. Lett. 2006,
8, 3203. (g) Chuang, S.-C.; Clemente, F. R.; Khan, S. I.; Houk, K. N.; Rubin,
Y. Org. Lett. 2006, 8, 4525. (h) Altable, M.; Filippone, S.; Mart´ın-Domenech,
A.; Gu¨ell, M.; Sola`, M.; Mart´ın, N. Org. Lett. 2006, 8, 5959. (i) Tada, T.; Ishida,
Y.; Saigo, K. Org. Lett. 2007, 9, 2083. (j) Thayumanavan, R.; Hawkins, B. C.;
Keller, P. A.; Pyne, S. G.; Ball, G. E. Org. Lett. 2008, 10, 1315. (k) Kokubo,
K.; Tochika, S.; Kato, M.; Sol, Y.; Oshima, T. Org. Lett. 2008, 10, 3335. (l)
Matsuo, Y.; Iwashita, A.; Abe, Y.; Li, C.-Z.; Matsuo, K.; Hashiguchi, M.;
Nakamura, E. J. Am. Chem. Soc. 2008, 130, 15429. (m) Tsuruoka, R.; Nagamachi,
T.; Murakami, Y.; Komatsu, M.; Minakata, S. J. Org. Chem. 2009, 74, 1691.
(n) Wang, G.-W.; Lu, Y.-M.; Chen, Z.-X. Org. Lett. 2009, 11, 1507.
4844 J. Org. Chem. Vol. 74, No. 13, 2009

AlternatiVe Type of Fullerene Products
TABLE 3. Reaction Times and Yields for the Conversion of 3-5
to 6-8 Promoted by BF3 ·Et2O at 50 °C
SCHEME 6. Conversion of 2-5 to 11-14 Promoted by
BF3 ·Et2O at 110 °C
substrate
reaction time (h)
product
yield (%)
cis-3
trans-3
cis-4
trans-4
cis-5
trans-5
1
1
1
1
3
3
6
6
7
7
8
8
81
79
84
83
80
81
SCHEME 5. Conversion of 2 to 9 Promoted by BF3 ·Et2O at
50 °C
TABLE 4. Reaction Times and Yields for the Conversion of 2-5
to 11-14 Promoted by BF3 ·Et2O at 110 °C
substrate
reaction time (h)
product
yield (%)
2
cis-3
trans-3
cis-4
trans-4
cis-5
1
1
1
1
1
3
3
11
12
12
13
13
14
14
33
84
74
82
79
33
28
trans-5
68.31 and 97.88 ppm for 9) indicates that the skeleton of product
1
9 is the same as that of its precursor 2. However, in the H
NMR spectrum of product 9 the methine proton on the
tetrahydrofuran ring showed much larger coupling constants
(11.4 and 3.9 Hz) due to the lack of the acetal moiety,
dramatically larger than the corresponding values (3.3 and 1.2
Hz) in compound 2.
Interestingly, when the reaction temperature was increased
to the refluxing temperature of toluene, the reaction of com-
pounds 2-5 with BF3 ·Et2O gave another type of products, that
is, methanofullerenes 11-14 (Scheme 6).
The reaction times and yields for the reaction of 2, cis-3,
trans-3, cis-4, trans-4, cis-5, and trans-5 with 200 equiv of
BF3 · Et2O at 110 °C affording products 11-14 are listed in
Table 4.
yields (79-84%). For example, the cis-3 and trans-3 afforded
product 6 in 81% and 79% yields, respectively.
Products 6 and 8 are known compounds, and their identities
were confirmed by comparison of their spectral data with the
reported ones.11a Product 7 showed 13C NMR and UV-vis
spectra similar to those of products 6 and 8.11a In the 13C NMR
spectrum of product 7, there were 29 lines including two half-
intensity ones in the 134-148 ppm range for the 58 sp2-carbons
of the C60 skeleton and two peaks (74.61 and 100.50 ppm) for
the two sp3-carbons of the C60 moiety, consistent with its Cs
molecular symmetry.
A carbonyl group was usually attached to the olefinic carbons
in the reported C60-fused dihydrofurans, which were commonly
prepared from the reaction of C60 with ꢀ-keto esters or
ꢀ-diketones in the presence of a base15 or a metal oxidant.16
However, alkyl- or aryl-substituted C60-fused dihydrofurans have
been much less investigated in the literature.11a,16b Our current
protocol of synthesizing the 3-alky- and 3-aryl-substituted C60-
fused dihydrofurans requires two steps starting from C60,
complementing our previous methodology, which demanded
three steps beginning with C60 via the synthesis of C60-fused
lactones,17 followed by reduction with DIBAL and then acid-
promoted dehydration.11a
Both cis and trans isomers gave the same product in nearly
the same yields. For example, the cis-4 and trans-4 isomers
afforded product 13 in 82% and 79% yields, respectively. It
should be noted that the competing product 9 was also isolated
in 48% yield from the reaction of 2 with BF3 ·Et2O at 110 °C.
Products 6-8 were also formed from the reaction of cis-3, trans-
3, cis-4, trans-4, cis-5, and trans-5 with BF3 ·Et2O and isolated
in 14%, 15%, 14%, 16%, 65%, and 68% yields, respectively.
The yields for products 11-14 could not be improved by
increasing the reaction temperature or prolonging the reaction
time for the reaction of compounds 2-5 with BF3 · Et2O at
110 °C.
To our surprise, treatment of compound 2 with BF3 ·Et2O in
toluene produced tolyl-substituted tetrahydrofuran 9, rather than
the corresponding C60-fused dihydrofuran product 10 (Scheme
5).
Full spectral characterization including HRMS, 1H NMR, 13
C
NMR, UV-vis, and IR spectra had also been carried out for
methanofullerenes 11-14. The δH at ca. 10 ppm, δC at ca. 190
ppm, and IR absorption at ca. 1720 cm-1 clearly demonstrated
the existence of the formyl group. The observation of no more
than 27 peaks for the 58 sp2-carbons of the C60 skeleton and
one peak at ca. 75 ppm for the two sp3-carbons of the C60 cage
agrees well with its Cs molecular symmetry.
The similarity of the 13C NMR patterns in the 134-155 ppm
range for the sp2-carbons of the C60 moiety between product 2
and product 9 together with the close chemical shifts for the
two sp3-carbons of the C60 cage (66.71 and 98.41 ppm for 2 vs
(15) (a) Ohno, M.; Yashiro, A.; Eguchi, S. Chem. Commun. 1996, 291. (b)
Jensen, A. W.; Khong, A.; Saunders, M.; Wilson, S. R.; Schuster, D. I. J. Am.
Chem. Soc. 1997, 119, 7303. (c) Wang, G.-W.; Zhang, T.-H.; Li, Y.-J.; Lu, P.;
Zhan, H.; Liu, Y.-C.; Murata, Y.; Komatsu, K. Tetrahedron Lett. 2003, 44, 4407.
(d) Zhang, T.-H.; Wang, G.-W.; Lu, P.; Li, Y.-J.; Peng, R.-F.; Liu, Y.-C.; Murata,
Y.; Komatsu, K. Org. Biomol. Chem. 2004, 2, 1698.
Methanofullerenes 11-14 are expected to have wide applica-
tion in further transformations due to the formyl group.18 Product
13 has been prepared by the reaction of C60 with an R-formyl
sulfonium ylide.18a However, the attempted synthesis of a
(16) (a) Li, C.; Zhang, D.; Zhang, X.; Wu, S.; Gao, X. Org. Biomol. Chem.
2004, 2, 3464. (b) Wang, G.-W.; Li, F.-B. Org. Biomol. Chem. 2005, 3, 794. (c)
Chen, X.; Wang, G.-W.; Murata, Y.; Komatsu, K. Chin. Chem. Lett. 2005, 16,
1327.
(18) (a) Hamada, M.; Hino, T.; Kinbara, K.; Saigo, K. Tetrahedron Lett.
2001, 42, 5069. (b) Ito, H.; Ishida, Y.; Saigo, K. Tetrahedron Lett. 2005, 46,
8757. (c) Ito, H.; Ishida, Y.; Saigo, K. Tetrahedron Lett. 2006, 47, 3095. (d) Ito,
H.; Ishida, Y.; Saigo, K. J. Org. Chem. 2006, 71, 4759.
(17) Wang, G.-W.; Li, F.-B.; Zhang, T.-H. Org. Lett. 2006, 8, 1355.
J. Org. Chem. Vol. 74, No. 13, 2009 4845

Wang et al.
SCHEME 7. Plausible Reaction Mechanism for the
Formation of Products 6-9 and 11-14
10 having no substituent than products 6-8 bearing an alky or
aryl substituent. Experimentally, product 9 was obtained
exclusively at lower temperature and was still a major product
at higher temperature. The fact that the cis and trans stere-
ochemistries of cis-3, trans-3, cis-4, trans-4, cis-5, and trans-5
did not affect the formation rates and yields of products 6-8
and 12-14 strongly substantiated the generation of the same
carbocation N, of which the cationic carbon had a sp2-
hybridization and trigonal planar geometry and would not have
any influence on the subsequent steps.
Conclusion
The reaction of C60 with freshly prepared RCH2CH2ONa/
RCH2CH2OH (R ) H, Me, Et, Ph) in anhydrous toluene in the
presence of air unexpectedly afforded fullerene products 2-5,
which contained a C60-fused tetrahydrofuran ring skeleton and
an acetal moiety. This novel type of fullerene products is
different from that of our previously reported C60-fused 1,3-
dioxolane derivative that was generated from the reaction of
C60 with PhCH2ONa/PhCH2OH, indicating that the reactions
with two different types of alkoxides proceeded in different
reaction pathways. Depending on the reaction conditions and
molecular structures, products 2-5 could be further converted
to C60-fused dihydrofurans 6-8, tolyl-substituted C60-fused
tetrahydrofuran 9, and methanofullerenes 11-14 bearing a
formyl group in the presence of boron trifluoride etherate.
Possible reaction mechanisms for the formation of these different
fullerene products 6-9 and 11-14 are proposed.
methanofullerene with the benzyl group replacing the ethyl
group in product 13 was unsuccessful. The failure was ascribed
to the steric repulsion between the C60 core and the benzyl group
and/or due to the formation of the less reactive dimethylsulfo-
nium enolate. In comparison, methanofullerene 14 having a
phenyl group, which should be more sterically demanding than
the benzyl group, could be obtained successfully by our protocol.
Even though the exact pathways for the formation of products
6-9 and 11-14 are not clear right now, a possible mechanism
for their formation is shown in Scheme 7.
Experimental Section
The BF3-induced C-O bond cleavage of the epoxy ring14f,19
and B(C6F5)3-induced O-O bond cleavage of the tert-butyl-
peroxy group20 are known in fullerene chemistry. Similarly, BF3
can complex with the oxygen atom of the RCH2CH2O moiety
(complex M) and then induce the C-O bond heterocleavage
to give cationic intermediate N. Proton elimination from
intermediate N via path (iv) (at a lower temperature of 50 °C)
results in C60-fused dihydrofurans 6-8. The C-O bond rupture
via path (v) (at a higher temperature of 110 °C) affords fullerenyl
cation O with a formyl group. Subsequent cyclization ac-
companied by the loss of H+ affords methanofullerenes 11-14.
Alternatively, methanofullerenes could also be generated by first
formation of C60-fused dihydrofurans, followed by BF3-induced
rearrangement. This possibility was evidenced by the fact that
the amount of formed C60-fused dihydrofurans at the early stage
of the reactions at 110 °C was significantly more than that at
the end of the reactions. This pathway was further supported
by a control experiment, which showed that C60-fused dihy-
drofuran 6 could be converted to methanofullerene 12 in the
presence of 200 equiv of BF3 ·Et2O at 110 °C. We believe that
the two parallel pathways leading to methanofullerenes 11-14
might operate at the same time. For R ) H, intermediate N
preferably reacts with toluene (the solvent) via path (vi) to give
product 9 rather than the corresponding C60-fused dihydrofuran
10. This phenomenon might be ascribed to the fact that toluene
can attack intermediate N much easier for R ) H because of
less steric hindrance and that it is more difficult to form product
Synthesis of Products 2-5 from the Reaction of C60 with
RCH2CH2ONa/RCH2CH2OH in the Presence of Air. A mixture
of C60 (50.4 mg, 0.07 mmol) and RCH2CH2ONa/RCH2OH (1.4 mL,
0.7 mmol RCH2CH2ONa, freshly prepared by treating 10 mL of
RCH2CH2OH with 115.0 mg of sodium) was completely dissolved
in anhydrous toluene (35 mL) with the aid of sonication. After
stirring at room temperature for the desired time, the reaction
mixture was filtered through a silica gel plug in order to remove
the unreacted sodium alkoxide and any other polar material. Then
the solvent was evaporated in vacuo, and the residue was separated
on a silica gel column with carbon disulfide as the eluent to give
unreacted C60 and compound 2 (cis-3, trans-3, cis-4, trans-4, cis-
5, trans-5).
2: 1H NMR (300 MHz, CS2/CDCl3) δ 1.45 (t, J ) 7.1 Hz, 3H),
3.88-3.99 (m, 3H), 4.32 (dq, J ) 9.5, 7.1 Hz, 1H), 6.15 (dd, J )
3.3, 1.2 Hz, 1H); 13C NMR (75 MHz, CS2/CDCl3 with Cr(acac)3
as relaxation reagent, all 1C unless indicated) δ 14.72, 48.22, 63.00,
66.71 (sp3-C of C60), 98.41 (sp3-C of C60), 102.68, 134.79, 136.51,
137.11, 137.31, 138.96, 139.12, 139.44, 139.53, 141.03, 141.12,
141.35, 141.46 (2C), 141.66 (4C), 141.77, 142.02 (2C), 142.08
(2C), 142.16 (2C), 142.40 (2C), 143.83, 144.13, 144.21 (2C), 144.59
(2C), 144.66 (3C), 144.70, 144.73, 144.77, 144.82 (2C), 145.11,
145.17, 145.38, 145.41, 145.51 (3C), 145.63, 145.74, 145.78,
145.83, 145.86, 146.86, 147.48, 148.32, 150.71, 154.93, 155.58;
FT-IR ν/cm-1 (KBr) 2968, 2920, 1511, 1463, 1430, 1367, 1315,
1211, 1170, 1101, 1038, 1017, 991, 937, 858, 766, 594, 575, 554,
526, 504, 477; UV-vis (CHCl3) λmax/nm (log ε) 253 (5.00), 314
(4.36), 427 (3.22), 696 (2.38); HRMS (ESI) calcd for C64H8NaO2
[M + Na]+ 831.0422, found 831.0416.
1
cis-3: H NMR (300 MHz, CDCl3) δ 1.12 (t, J ) 7.5 Hz, 3H),
(19) Huang, S.; Xiao, Z.; Wang, F.; Zhou, J.; Yuan, G.; Zhang, S.; Chen,
Z.; Thiel, W.; Schleyer, P. R.; Zhang, X.; Hu, X.; Chen, B.; Gan, L. Chem.sEur.
J. 2005, 11, 5449.
(20) Wang, F.; Xiao, Z.; Yao, Z.; Jia, Z.; Huang, S.; Gan, L.; Zhou, J.; Yuan,
G.; Zhang, S. J. Org. Chem. 2006, 71, 4374.
1.80-1.92 (m, 2H), 1.89 (d, J ) 7.0 Hz, 3H) 3.82 (dt, J ) 9.5, 6.5
Hz, 1H), 4.09 (dq, J ) 7.0, 3.9 Hz, 1H), 4.28 (dt, J ) 9.5, 6.5 Hz,
1H), 5.97 (d, J ) 3.9 Hz, 1H); 13C NMR (75 MHz, CDCl3 with
Cr(acac)3 as relaxation reagent, all 1C unless indicated) δ 11.03,
4846 J. Org. Chem. Vol. 74, No. 13, 2009

AlternatiVe Type of Fullerene Products
12.94, 23.07, 53.37, 69.83, 71.66 (sp3-C of C60), 99.41 (sp3-C of
C60), 105.51, 135.29, 137.87, 138.07, 138.18, 139.64, 139.74,
139.87, 140.25, 141.67, 141.71, 142.00, 142.15, 142.21, 142.38
(2C), 142.40 (2C), 142.50, 142.55, 142.76, 142.79 (2C), 142.85
(2C), 143.06, 143.10, 144.45, 144.86 (2C), 144.99, 145.22,
145.30 (2C), 145.37 (3C), 145.39, 145.55, 145.78, 145.81, 146.05
(2C), 146.11, 146.17, 146.20, 146.23, 146.38, 146.39, 146.48,
146.52, 146.55, 146.78, 147.53, 148.19, 148.99, 152.00, 153.35,
156.55; FT-IR ν/cm-1 (KBr) 2955, 2869, 1451, 1428, 1180, 1103,
1074, 998, 966, 943, 765, 592, 575, 553, 526, 499, 476; UV-vis
(CHCl3) λmax/nm (log ε) 256 (5.01), 313 (4.51), 427 (3.38), 696
(2.40); HRMS (ESI) calcd for C66H12NaO2 [M + Na]+ 859.0735,
found 859.0719.
8H), 7.76-7.79 (m, 2H); 13C NMR (75 MHz, CS2/CDCl3 with
Cr(acac)3 as relaxation reagent, all 1C unless indicated) δ 36.00,
64.43, 68.87, 71.96 (sp3-C of C60), 98.35 (sp3-C of C60), 104.40,
126.24, 127.86 (3C), 128.29 (2C), 128.77 (2C), 131.40 (2C), 133.45,
134.58, 137.32, 137.36, 137.41, 138.50, 139.09 (2C), 139.16,
139.43, 140.95, 141.27, 141.39, 141.62, 141.65, 141.74, 141.75,
141.78, 141.80, 141.93, 141.95, 141.99, 142.22 (4C), 142.42,
142.44, 143.82, 144.18, 144.23, 144.38, 144.51, 144.60, 144.77
(4C), 144.87, 145.08, 145.20, 145.31, 145.37, 145.45, 145.52,
145.63 (3C), 145.73, 145.78, 145.84, 145.93, 145.99 (2C), 146.91,
147.58, 148.32, 150.80, 152.10, 155.19; FT-IR ν/cm-1 (KBr) 2918,
2850, 1494, 1453, 1428, 1181, 1127, 1098, 996, 942, 860, 745,
696, 576, 553, 543, 526; UV-vis (CHCl3) λmax/nm (log ε) 256
(4.92), 314 (4.46), 427 (3.28), 693 (2.31); HRMS (ESI) calcd for
C76H16NaO2 [M + Na]+ 983.1048, found 983.1050.
1
trans-3: H NMR (300 MHz, CDCl3) δ 1.11 (t, J ) 7.4 Hz,
3H), 1.87 (sextet, J ) 7.1 Hz, 2H), 1.96 (d, J ) 7.2 Hz, 3H), 3.85
(dt, J ) 9.4, 6.7 Hz, 1H), 4.14 (q, J ) 7.2 Hz, 1H), 4.25 (dt, J )
9.4, 6.7 Hz, 1H), 5.84 (s, 1H); 13C NMR (75 MHz, CDCl3/CS2
with Cr(acac)3 as relaxation reagent, all 1C unless indicated) δ
10.50, 18.46, 22.60, 52.06, 69.57, 70.96 (sp3-C of C60), 98.09 (sp3-C
of C60), 109.78, 136.18, 136.46, 137.30, 137.91, 139.00, 139.07,
139.25, 139.39, 140.88, 141.03, 141.34, 141.37, 141.44, 141.62
(3C), 141.70, 141.72, 141.76, 142.00, 142.03, 142.08, 142.12,
142.18, 142.36, 142.43, 143.84, 144.14, 144.18 (2C), 144.51,
144.58, 144.60, 144.67 (3C), 144.70, 144.77, 144.92, 145.10
(2C), 145.33 (3C), 145.45, 145.49, 145.53, 145.55, 145.75 (2C),
145.85, 145.88, 146.86, 147.47, 148.95, 150.44, 152.99, 155.64;
FT-IR ν/cm-1 (KBr) 2921, 1452, 1426, 1174, 1102, 998, 953, 765,
596, 574, 524, 477; UV-vis (CHCl3) λmax/nm (log ε) 256 (5.00),
312 (4.51), 428 (3.36), 694 (2.38); HRMS (ESI) calcd for
C66H12NaO2 [M + Na]+ 859.0735, found 859.0723.
trans-5: 1H NMR (300 MHz, CS2/CDCl3) δ 3.13 (t, J ) 6.6 Hz,
2H), 4.10 (dt, J ) 9.3, 6.6 Hz, 1H), 4.55 (dt, J ) 9.3, 6.6 Hz, 1H),
5.22 (s, 1H), 6.13 (s, 1H), 7.13-7.36 (m, 6H), 7.45 (t, J ) 7.5 Hz,
2H), 7.86 (d, J ) 7.5 Hz, 2H); 13C NMR (75 MHz, CS2/CDCl3
with Cr(acac)3 as relaxation reagent, all 1C unless indicated) δ
36.38, 64.81, 69.03, 73.35 (sp3-C of C60), 99.11 (sp3-C of C60),
109.16, 126.66, 128.14, 128.64 (2C), 128.68 (2C), 129.26 (2C),
129.43 (2C), 136.72, 136.90, 137.81, 138.86, 138.92, 139.37,
139.50, 139.70, 139.73, 139.93, 141.57, 141.89 (3C), 142.04,
142.09, 142.23 (2C), 142.33, 142.37 (2C), 142.64, 142.69, 142.71,
142.76, 142.78, 142.90, 142.95, 144.40, 144.65, 144.77, 144.79,
145.03, 145.13 (2C), 145.18, 145.23, 145.24, 145.27, 145.30 (3C),
145.69, 145.77 (2C), 145.98, 146.01, 146.08, 146.15 (2C), 146.23,
146.39, 146.40, 146.51, 147.53, 148.12, 148.70, 150.48, 154.08,
155.76; FT-IR ν/cm-1 (KBr) 2918, 2862, 1512, 1493, 1452, 1428,
1355, 1186, 1169, 1093, 1054, 1013, 987, 939, 839, 746, 697, 575,
563, 553, 525, 490; UV-vis (CHCl3) λmax/nm (log ε) 256 (4.98),
314 (4.51), 427 (3.31), 693 (2.35); HRMS (ESI) calcd for
C76H16NaO2 [M + Na]+ 983.1048, found 983.1045.
Synthesis of Products 2-5 from the Reaction of C60 with
RCH2CH2ONa/RCH2CH2OH and RCH2CHO in the Presence of
Air. A mixture of C60 (50.4 mg, 0.07 mmol) and RCH2CH2ONa/
RCH2CH2OH (1.4 mL, 0.7 mmol RCH2CH2ONa, freshly prepared
by treating 10 mL of RCH2CH2OH with 115.0 mg of sodium) was
completely dissolved in anhydrous toluene (35 mL) with the aid
of sonication. Then RCH2CHO (0.07 mmol) was added. After
stirring at room temperature for the desired time, the same workup
as above gave the unreacted C60 and compound 2 (cis-3, trans-3,
cis-4, trans-4, cis-5, trans-5).
Conversion of Compounds 3-5 to Products 6-8 in the Pres-
ence of Boron Trifluoride Etherate at 50 °C. C60-fused tetrahy-
drofuran cis-3 (trans-3, cis-4, trans-4, cis-5, or trans-5) (0.015
mmol) was dissolved in toluene (7 mL) with the aid of sonication.
Then 1.5 mmol of boron trifluoride etherate was added. After
stirring at 50 °C for the desired time, the reaction mixture was
filtered through a silica gel plug. Then the solvent was evaporated
in vacuo, and the residue was separated on a silica gel column with
carbon disulfide as the eluent to give compound 6 (7 or 8).
7: 1H NMR (300 MHz, CS2/CDCl3) δ 1.54 (t, J ) 7.4 Hz, 3H),
2.75 (dq, J ) 7.2, 1.8 Hz, 2H), 6.96 (t, J ) 1.8 Hz, 1H); 13C NMR
(75 MHz, CS2/DMSO-d6 with Cr(acac)3 as relaxation reagent, all
2C unless indicated) δ 12.36 (1C), 19.21 (1C), 74.61 (1C, sp3-C
of C60), 100.50 (1C, sp3-C of C60), 117.04 (1C), 134.80, 135.82,
138.51 (1C), 138.61, 139.27, 140.42, 140.75, 140.94, 141.07,
141.11, 141.47, 141.50 (4C), 141.72, 143.17, 143.18, 143.84,
143.90, 144.00, 144.15, 144.41, 144.50, 144.68, 144.76, 144.86,
144.90, 144.94, 145.03, 146.07 (1C), 146.81 (1C), 147.95; FT-IR
ν/cm-1 (KBr) 2959, 2919, 1666, 1629, 1429, 1182, 1121, 1051,
1006, 980, 942, 901, 846, 767, 596, 574, 526; UV-vis (CHCl3)
1
cis-4: H NMR (300 MHz, CDCl3) δ 1.02 (t, J ) 7.4 Hz, 3H),
1.39 (t, J ) 7.4 Hz, 3H), 1.58 (sextet, J ) 7.4 Hz, 2H), 1.77-1.86
(m, 2H), 2.33-2.46 (m, 2H), 3.84-3.94 (m, 2H), 4.32 (dt, J )
9.6, 6.3 Hz, 1H), 6.07 (d, J ) 3.9 Hz, 1H); 13C NMR (75 MHz,
CDCl3 with Cr(acac)3 as relaxation reagent, all 1C unless indicated)
δ 12.88, 13.96, 19.41, 22.18, 31.59, 60.07, 67.75, 71.07 (sp3-C of
C60), 99.41 (sp3-C of C60), 104.04, 135.09, 137.62, 137.68, 137.79,
139.40, 139.50, 139.53, 139.90, 141.40, 141.45, 141.71, 141.90,
141.94, 142.13 (2C), 142.16 (2C), 142.25, 142.31, 142.52, 142.54
(2C), 142.61 (2C), 142.81, 142.87, 144.21, 144.62 (2C), 144.75,
144.97, 145.04, 145.08, 145.10 (2C), 145.12 (2C), 145.32, 145.60,
145.65, 145.80 (2C), 145.83, 145.92, 145.95, 145.97, 146.12,
146.15, 146.24, 146.26, 146.30, 146.46, 147.27, 147.93, 148.84,
151.70, 153.39, 156.36; FT-IR ν/cm-1 (KBr) 2955, 2925, 2868,
1459, 1428, 1377, 1341, 1304, 1177, 1152, 1137, 1104, 1082, 995,
946, 894, 766, 576, 563, 553, 527, 479; UV-vis (CHCl3) λmax/nm
(log ε) 257 (4.89), 313 (4.53), 428 (3.40), 695 (2.47); HRMS (ESI)
calcd for C68H16NaO2 [M + Na]+ 887.1048, found 887.1040.
1
trans-4: H NMR (300 MHz, CDCl3) δ 1.01 (t, J ) 7.4 Hz,
3H), 1.44 (t, J ) 7.4 Hz, 3H), 1.60 (sextet, J ) 7.2 Hz, 2H), 1.84
(penta, J ) 7.1 Hz, 2H), 2.42 (penta, J ) 7.3 Hz, 2H), 3.86-3.95
(m, 2H), 4.29 (dt, J ) 9.0, 7.2 Hz, 1H), 5.97 (s, 1H); 13C NMR
(75 MHz, CDCl3 with Cr(acac)3 as relaxation reagent, all 1C unless
indicated) δ 13.20, 13.91, 19.26, 26.54, 31.50, 59.61, 67.98, 71.52
(sp3-C of C60), 98.41 (sp3-C of C60), 107.90, 136.33, 136.71, 137.72,
138.31, 139.37, 139.40, 139.48, 139.70, 141.21, 141.37, 141.66,
141.69, 141.80, 141.96, 141.98, 142.02, 142.09 (3C), 142.37,
142.39, 142.45, 142.48, 142.55, 142.71, 142.80, 144.20, 144.51,
144.55 (2C), 144.84, 144.88, 145.00 (2C), 145.04 (2C), 145.13,
145.16, 145.22, 145.49, 145.62, 145.71 (3C), 145.84, 145.88 (2C),
145.90, 146.12, 146.15, 146.19, 146.25, 147.25, 147.86, 149.14,
150.87, 153.47, 156.32; FT-IR ν/cm-1 (KBr) 2955, 2925, 2866,
1459, 1428, 1378, 1358, 1171, 1109, 1094, 998, 944, 840, 766,
575, 556, 527, 480; UV-vis (CHCl3) λmax/nm (log ε) 259 (4.91),
313 (4.52), 428 (3.37), 691 (2.42); HRMS (ESI) calcd for
C68H16NaO2 [M + Na]+ 887.1048, found 887.1056.
λ
max/nm (log ε) 255 (5.02), 314 (4.51), 426 (3.35), 691 (2.35);
HRMS (ESI) calcd for C64H6NaO [M + Na]+ 813.0316, found
813.0308.
1
cis-5: H NMR (300 MHz, CS2/CDCl3) δ 3.19 (t, J ) 6.4 Hz,
2H), 4.16 (dt, J ) 9.4, 6.4 Hz, 1H), 4.69 (dt, J ) 9.4, 6.4 Hz, 1H),
5.10 (d, J ) 3.7 Hz, 1H), 6.14 (d, J ) 3.7 Hz, 1H), 7.19-7.37 (m,
Conversion of 2 to 9 Promoted by BF3 ·Et2O at 50 °C.
Compound 2 (12.4 mg, 0.015 mmol) was dissolved in toluene (7
J. Org. Chem. Vol. 74, No. 13, 2009 4847

Wang et al.
mL) with the aid of ultrasonication. Then boron trifluoride etherate
(200 µL, 1.5 mmol) was added. After stirring at 50 °C for 3 h, the
reaction mixture was filtered through a silica gel plug. Then the
solvent was evaporated in vacuo, and the residue was separated on
a silica gel column with carbon disulfide/toluene as the eluent to
give the crude product along with recovered compound 2 (1.5 mg,
12%). Further HPLC purification on a Cosmosil Buckyprep column
148.59, 190.71 (1C, CHO); FT-IR ν/cm-1 (KBr) 2921, 2850, 1718,
1540, 1460, 1428, 1315, 1184, 1116, 1063, 797, 709, 574, 526,
494; UV-vis (CHCl3) λmax/nm (log ε) 259 (5.09), 326 (4.54), 427
(3.37), 690 (2.17); HRMS (MALDI FT-ICR) calcd for C62H2O [M]-
762.0106, found 762.0098.
12: 1H NMR (300 MHz, CS2/C6D4Cl2) δ 2.20 (s, 3H), 10.42 (s,
1H); 13C NMR (75 MHz, CS2/C6D4Cl2 with Cr(acac)3 as relaxation
reagent, all 2C unless indicated) δ 11.70 (1C), 45.43 (1C), 76.18
(sp3-C of C60), 135.40, 135.41, 138.20, 138.44, 141.35, 141.45,
141.86, 142.39, 143.27 (6C), 143.34 (1C), 143.37, 143.48 (1C),
144.01, 144.08, 144.71, 144.88 (1C), 144.93 (6C), 144.97 (1C),
145.02, 145.33, 145.45, 145.49, 145.54 (4C), 145.56, 146.05,
147.09, 193.38 (1C, CHO); FT-IR ν/cm-1 (KBr) 2922, 2852, 1716,
1507, 1427, 1380, 1261, 1184, 1084, 1039, 951, 868, 797, 736,
706, 573, 557, 525; UV-vis (CHCl3) λmax/nm (log ε) 259 (5.09),
327 (4.56), 429 (3.40), 688 (2.26); HRMS (MALDI FT-ICR) calcd
for C63H4O [M]- 776.0262, found 776.0268.
1
(4.6 mm × 250 mm) gave pure compound 9 (9.3 mg, 72%). H
NMR (300 MHz, CS2/CDCl3) δ 2.47 (s, 3H), 3.83 (dd, J ) 12.0,
11.4 Hz, 1H), 4.10 (dd, J ) 12.0, 3.9 Hz, 1H), 6.24 (dd, J ) 11.4,
3.9 Hz, 1H), 7.34 (d, J ) 7.8 Hz, 2H), 7.75 (d, J ) 7.8 Hz, 2H);
13C NMR (75 MHz, CS2/CDCl3 with Cr(acac)3 as relaxation reagent,
all 1C unless indicated) δ 20.99, 50.46, 68.31 (sp3-C of C60), 78.27,
97.88 (sp3-C of C60), 126.13 (2C), 128.99 (2C), 134.48, 135.33,
136.07, 136.93, 137.48, 137.52, 138.91, 139.25, 139.39, 139.51,
140.66, 141.08, 141.14, 141.43, 141.48, 141.52 (2C), 141.54, 141.65
(2C), 141.84, 141.95, 141.98 (2C), 142.02, 142.06, 142.21, 142.25,
143.75, 143.93 (2C), 144.07, 144.20, 144.43, 144.49, 144.52 (2C),
144.55, 144.62 (3C), 144.77, 144.90, 145.18, 145.29, 145.38 (2C),
145.43 (2C), 145.56, 145.64 (2C), 145.66, 145.73, 146.73, 147.33,
148.15, 149.47, 154.22, 154.92; FT-IR ν/cm-1 (KBr) 2922, 2852,
1512, 1459, 1428, 1374, 1305, 1264, 1175, 1110, 1016, 995, 811,
770, 600, 565, 525; UV-vis (CHCl3) λmax/nm (log ε) 254 (5.08),
314 (4.61), 428 (3.45), 691 (2.36); HRMS (ESI) calcd for
C69H10NaO [M + Na]+ 877.0629, found 877.0617.
14: 1H NMR (300 MHz, CS2/CDCl3) δ 7.51-7.60 (m, 3H), 7.91
(d, J ) 7.5 Hz, 2H), 10.45 (s, 1H); 13C NMR (75 MHz, CS2/CDCl3
with Cr(acac)3 as relaxation reagent, all 2C unless indicated) δ 57.27
(1C), 74.11 (sp3-C of C60), 128.33, 128.74 (1C), 129.57 (1C),
131.98, 137.52, 137.90, 140.19, 140.38, 140.95, 141.07, 141.26,
141.35, 142.09, 142.15 (3C), 142.18, 142.26, 142.38 (1C), 142.90,
143.08, 143.63 (1C), 143.68, 143.78, 143.84, 143.91 (5C), 143.95,
144.32, 144.39 (4C), 144.42, 144.55, 144.59, 145.55, 189.08 (1C,
CHO); FT-IR ν/cm-1 (KBr) 2923, 2853, 1722, 1507, 1461, 1427,
1377, 1261, 1183, 1094, 1024, 801, 698, 575, 525; UV-vis (CHCl3)
Conversion of Compounds 2-5 to Products 11-14 in the
Presence of Boron Trifluoride Etherate at 110 °C. Compound 2
(cis-3, trans-3, cis-4, trans-4, cis-5, or trans-5) (0.015 mmol) was
dissolved in toluene (7 mL) with the aid of sonication. Then 3.0
mmol of boron trifluoride etherate was added. After stirring at the
refluxing temperature (with an oil bath of 120 °C) for the desired
time, the reaction mixture was filtered through a silica gel plug.
Then the solvent was evaporated in vacuo, and the residue was
separated on a silica gel column with carbon disulfide as the eluent
to give product 9 (6, 7, or 8) and then product 11 (12, 13, or 14).
λ
max/nm (log ε) 259 (5.09), 327 (4.58), 428 (3.38), 691 (2.29);
HRMS (MALDI FT-ICR) calcd for C68H6O [M]- 838.0419, found
838.0411.
Acknowledgment. The authors are grateful for the financial
support from the National Natural Science Foundation of China
(Nos. 20572105 and 20621061) and the National Basic Research
Program of China (2006CB922003).
1
11: H NMR (300 MHz, CS2/C6D4Cl2) δ 4.55 (d, J ) 5.0 Hz,
1H), 10.26 (d, J ) 5.0 Hz, 1H); 13C NMR (75 MHz, CS2/C6D4Cl2,
all 2C unless indicated) δ 44.96 (1C), 71.09 (sp3-C of C60), 137.19,
139.32, 141.78 (4C), 142.40, 142.61, 142.72, 143.02, 143.57 (8C),
143.71, 144.33, 144.42, 145.13 (1C), 145.18 (4C), 145.21 (1C),
145.25 (4C), 145.31, 145.44, 145.75, 145.82 (6C), 145.86, 146.03,
Supporting Information Available: NMR spectra of com-
pounds 2-9, 11-14. This material is available free of charge
via the Internet at http://pubs.acs.org.
JO9005848
4848 J. Org. Chem. Vol. 74, No. 13, 2009