Efficient cage-opening cascade process for the preparation of water-encapsulated [60]fullerene derivatives

Article abstract of DOI:10.1021/ol9009305

Cage-opened fullerenes with 18-membered-ring orifices have been prepared starting from fullerene-mixed peroxides. The key transformation Involves a cascade sequence Including a deketalization, a S_N2' epoxide opening reaction, and a formal 3,3-δ

Full text of DOI:10.1021/ol9009305

ORGANIC
LETTERS
2009
Vol. 11, No. 13
2772-2774
Efficient Cage-Opening Cascade
Process for the Preparation of
Water-Encapsulated [60]Fullerene
Derivatives
Qianyan Zhang,† Zhenshan Jia,† Shuming Liu,† Gang Zhang,† Zuo Xiao,‡
Dazhi Yang,‡ Liangbing Gan,*,†,‡ Zheming Wang,*,‡ and Yuliang Li†
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory for Organic
Solids, Institute of Chemistry, Chinese Academy of Science, Beijing 100080, China,
and Key Laboratory of Bioorganic Chemistry and Molecular Engineering of the
Ministry of Education, College of Chemistry and Molecular Engineering, Peking
UniVersity, Beijing 100871, China
gan@pku.edu.cn; zmw@pku.edu.cn
Received April 29, 2009
ABSTRACT
Cage-opened fullerenes with 18-membered-ring orifices have been prepared starting from fullerene-mixed peroxides. The key transformation
involves a cascade sequence including a deketalization, a SN2′ epoxide opening reaction, and a formal 3,3-σ rearrangement. The 18-membered-
ring orifice is big enough for water encapsulation under mild conditions. Single crystal X-ray structures were obtained for both the empty and
water-encapsulated fullerene derivatives.
Cage-opened fullerene derivatives with suitable orifice could
allow incorporation of atoms or small molecules inside the
cavity to form endohedral fullerene derivatives. Several
molecules such as He, H2, H2O, CO, NH3 and CH4 have
been incorporated into cage-opened fullerene derivatives.2-10
Pure H2@C60 has been prepared through the opening-
insertion-closing pathway (the molecular surgery method).11
To fully explore such a strategy, efficient cage-opening
methods are still needed. At present the number of known
cage-opened fullerene derivatives is quite limited, especially
those with an orifice large enough for encapsulation purposes.
We have been studying the chemistry of fullerene-mixed
peroxides and prepared several cage-opened fullerene deriva-
tives starting from the hexa-adduct C60(OOtBu)6.6a Here we
report the formation of new cage-opened derivatives 1 and
2 through an unexpected cascade process as the fullerene
† Chinese Academy of Science.
‡ Peking University.
(1) (a) Rubin, Y. Chem.sEur. J. 1997, 3, 1009. (b) Rubin, Y. Top. Curr.
Chem. 1999, 199, 67. (c) Murata, M.; Murata, Y.; Komatsu, K. Chem.
Commun. 2008, 6083.
(4) (a) Iwamatsu, S.-i.; Uozaki, T.; Kobayashi, K.; Re, S.; Nagase, S.;
Murata, S. J. Am. Chem. Soc. 2004, 126, 2668. (b) Iwamatsu, S.-i; Murata,
S. Synlett 2005, 14, 2117.
(2) Stanisky, C. M.; Cross, R. J.; Saunders, M.; Murata, M.; Murata,
Y.; Komatsu, K. J. Am. Chem. Soc. 2005, 127, 299
.
(3) Rubin, Y.; Jarrosson, T.; Wang, G.-W.; Bartberger, M. D.; Houk,
(5) Iwamatsu, S.-i.; Stanisky, C. M.; Cross, R. J.; Saunders, M.;
Mizorogi, N.; Nagase, S.; Murata, S. Angew. Chem., Int. Ed. 2006, 45,
5337.
K. N.; Schick, G.; Saunders, M.; Cross, R. J. Angew. Chem., Int. Ed. 2001,
40, 1543
.
10.1021/ol9009305 CCC: $40.75
Published on Web 06/03/2009
 2009 American Chemical Society

C-C bond cleavage steps. The orifices in these compounds
are suitable for the formation of water-encapsulated com-
plexes.
hemiketal fullerene carbon is slightly shifted to lower field
at 110.2 ppm compared with its precursor 5.
We have previously investigated the reaction between
fullerene diketones and anilines. The resulting fullerene
hemiketal amino-ketal derivatives were proved to be useful
precursors for cage-opened fullerene derivatives.6a However,
to our surprise, the reaction of 6 and aniline directly led to
the formation of two orifice-enlarged compounds 1a and 2a
(Scheme 2). In the formation of 1a, all three t-butoxyl groups
The oxahomofullerene 3 was prepared in three steps as
we reported previously.12 Treatment of 3 with AgClO4 and
water converted the chlorine atom into a hydroxyl group and
resulted in the formation of 4. The hemiketal hydroxyl group
in 4 could be selectively acylated with acetic anhydride to
form the diol 5, which was oxidized with diacetoxyliodo-
benzene (DIB) to give the corresponding diketone derivative
6 (Scheme 1). Protection of the hemiketal moiety was
Scheme 2. Cage-Opening by Cascade Process
Scheme 1. Preparation of Cage-Opened Precursor
in 6 were removed. The remaining t-butylperoxo group in
compound 2a could be reduced to the hydroxyl group in 1a
with CuBr in excellent yield. Further optimization showed
that isolation of 6 was not necessary before the addition of
aniline. The DIB oxidation and the amination could be
carried out in one pot with improved overall yield (54% for
2a). Other aniline derivatives such as the 4-bromo and
4-isopropyl anilines gave similar results with slightly dif-
ferent yields. The more electron rich 4-isopropyl aniline gave
relatively higher yield of the dihydroxyl derivative 1.
A possible mechanism for the amine-initiated cage-opening
process is shown in Scheme 3. The first step is the aminolysis
of the hemiketal ester to form the allyl anion intermediate
A with four carbonyl groups. Loss of t-butoxide ion from A
results in the formation of B with an epoxy moiety. Addition
of another amine molecule to B opens the epoxide through
the SN2′ mechanism. The resulting intermediate C undergoes
a formal 3,3-σ rearrangement process to cleave another
fullerene C-C bond to form intermediate D. This step is
probably driven mainly by ring strain. Cleavage of the
fullerene C-C bond in this step allows the central pentagon
to be lifted up from the spherical surface and become
completely planar (see crystal structure of 1a below). In the
final step, a third amine molecule reacts with the less
hindered carbonyl group on the lifted pentagon to form
compound 2. Activation of this carbonyl group by H-bond
from the adjacent OH group must play a key role for the
observed selective imination besides steric preference.
necessary for oxidation with DIB. Direct oxidation of 4 gave
complicated mixture of products.
The structure of compound 3 was previously confirmed
by single crystal X-ray analysis.12 Compounds 4 and 5 are
analogous to 3. Their NMR spectra show similar pattern.
The unique hemiketal fullerene carbon appears at 108.0,
107.8, and 107.7 ppm on the 13C NMR spectrum for
compounds 3, 4, and 5, respectively. The diketone derivative
6 showed two carbonyl groups at 194.6 and 192.0 ppm. Its
(6) (a) Xiao, Z.; Yao, J. Y.; Yang, D. Z.; Wang, F. D.; Huang, S. H.;
Gan, L. B.; Jia, Z. S.; Jiang, Z. P.; Yang, X. B.; Zheng, B.; Yuan, G.;
Zhang, S. W.; Wang, Z. M. J. Am. Chem. Soc. 2007, 129, 16149. (b)
Pankewitz, T.; Klopper, W. Chem. Phys. Lett. 2008, 465, 48.
(7) Whitener, K. E., Jr.; Frunzi, M.; Iwamatsu, S. -i.; Murata, S.; Cross,
R. J.; Saunders, M. J. Am. Chem. Soc. 2008, 130, 13996.
(8) Stanisky, C. M.; Cross, R. J.; Saunders, M. J. Am. Chem. Soc. 2009,
131, 3392.
(9) Wang, G. W.; Wu, P.; Tian, Z. G. Eur. J. Org. Chem. 2009, 7, 1032.
(10) Whitener; Jr, K. E.; Cross, R. J.; Saunders, M; Iwamatsu, S. -i;
Murata, S.; Mizorogi, N.; Nagase, S. J. Am. Chem. Soc. 2009, 131, 6338.
(11) (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) Matsuo, Y.; Isobe, H.; Tanaka, T.; Murata, Y.; Murata, M.;
Komatsu, K.; Nakamura, E. J. Am. Chem. Soc. 2005, 127, 17148. (d) Murata,
Y.; Maeda, S.; Murata, M.; Komatsu, K. J. Am. Chem. Soc. 2008, 130,
6702.
(12) Huang, S. H.; Xiao, Z.; Wang, F. D.; Zhou, J.; Yuan, G.; Zhang,
S. W.; Chen, Z. F.; Thiel, W.; Schleyer, P. R.; Zhang, X.; Hu, X. Q.; Chen,
B. C.; Gan, L. B. Chem.sEur. J. 2005, 11, 5449.
Org. Lett., Vol. 11, No. 13, 2009
2773

Scheme 3. Possible Pathway for the Formation of 2
Figure 1. Molecular structures of 1a (left) and H2O@1a (right).
The oxygen atom of the encapsulated water molecule was drawn
as the spacefill model. For clarity only the hydrogen atoms of the
OH groups were shown. Color scheme: gray, C; red, O; blue, N;
green, H.
of 1a and H2O@1a, with the H-bond of O-H···N geometry:
2.71 to 2.78 Å and 131 to 133°. The encapsulated water
molecule does not have noticeable effect on the cage
structure. Water content was estimated to be 38% as
determined from the refined occupancy in the structure
refinement, which is close to the 1H NMR determined value
(40%) for the same sample. This sample was obtained by
heating the solution of 1a in toluene/water for 5 h. Further
heating for 24 h could increase the water content up to 87%.
In summary, fullerene-mixed peroxides have been con-
verted to cage-opened fullerenes with an 18-membered
orifice, suitable for water encapsulation. The key transforma-
tion involves a cascade sequence including a deketalization,
a SN2′ epoxide opening reaction, and a formal 3,3-σ
rearrangement. Work is in progress to further modify the
orifice and to incorporate other atoms or molecules into the
cavity of the cage-opened fullerene derivatives.
In agreement with the above explanation for the selectivity
of the last step, the 1H NMR spectra of compounds 1 and 2
indicate a strong intramolecular H-bond between the imino
and OH groups. Their chemical shifts (7.9 ppm for 1a and
7.6 ppm for 2a) appear at a much lower field than those of
OH groups attached to a normal fullerene carbon such as
the vicinal diol moiety of 4 and 5 which are less than 6 ppm.
The 13C NMR spectra of compounds 1 and 2 showed the
expected number of carbonyl signals. But resolution of the
IR spectrum is not high enough, and just one intense band
around 1745 cm-1 was observed for the four carbonyl groups.
Crystals of 1a and H2O@1a were obtained by slow
evaporation of their CS2/EtOH solution. Their X-ray struc-
tures are essentially the same in terms of the unit cell
parameters and the molecular geometries (Figure 1). The
intramolecular H-bonds between the imino and the hydroxyl
groups are clearly observed from the single crystal structures
Acknowledgment. Financial support is provided by
NNSFC (Grants 20632010, 20772004, and 20821062) and
MOST (2006CB806201).
Supporting Information Available: Experimental pro-
cedure and spectroscopic data for all new compounds and
cif files for compounds 1a and H2O@1a with lattice solvents,
1.2 CS2 and 0.3 EtOH. This material is available free of
charge via the Internet at http://pubs.acs.org.
OL9009305
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Org. Lett., Vol. 11, No. 13, 2009