a
Table 1 Additive effect on 1-mediated reduction of acetophenone with NaBH4
Entry
1?24H2O (mmol)
Additive (mmol)
Temp. (uC)
Product (mmol)
TOF (h21
)
1
2
3
4
5
6
0
0
0
0
0
25
25
25
50
25
25
24
13
74
106
160
250
—
—
55
80
—
186
2.7 (c-CyD)b
1.34
1.34
0
(Me2N)2CH2 0.73
(Me2N)2CH2 0.73
EtONa 0.73
(Me2N)2CH2 3.5
EtONa 3.5
(Me2N)3CH 0.73
(Me2N)3CH 0.73
(Me2N)3CH 0.73
EtONa 0.73
(MeS)3CH 0.73
1.34
7
1.34
25
536
400
8
9
10
0
1.34
1.34
25
25
25
140
211
172
—
157
129
11
a
1.34
25
67
50
Condition: acetophenone (833.3 mmol), NaBH4 (131.5 mmol except for Entry 7, 650 mmol for Entry 7), DMSO (10% H2O) (2.7 mL), 1 h.
c-cyclodextrin (2.7 mmol) is used instead of 1.
b
allows for the preferential reduction of a CLC bond over a CLO or
absorbance of new band (lmax 1075 nm) due to
c-cyclodextrin-bicapped C60 monoanion (112) similarly to
TTC reduction (Fig. 2), suggesting that 2 serves as one
electron donor in the reaction.
CMN functionality. In control experiments, we confirm that 3 does
not reduce these substrates. Spectral change in the reaction of 2
(generated by diborate 3) with TTC (colourless) is shown in Fig. 2,
which indicates that the formation of deep red triphenylformazan
In the catalytic reduction of acetophenone, reversible formation
of 2 (lmax 950 nm) from 112 (lmax 1075 nm) was observed for 1 h
by spectroscopy. In the presence of O2, irreversible change takes
place. In the examination of the evolution of the reaction with time
under the entry 3 conditions, the product yield (mmol) was 0 at 0 h,
63 at 0.3 h, and 74 at 1 h.
(6, lmax 517 nm) and supramolecular C60 monoanion (112
,
lmax 1075 nm).
In conclusion, the supramolecular C60 dianion (2) is able to
reduce N–N+, CLC–EWG and CLO bonds to provide the
respective dihydro derivative. The 1-mediated reduction of
acetophenone with NaBH4 in the presence of (Me2N)2CH2 and
EtONa gives TOF (h21) of 400. Irradiation is not necessary for
this reaction.
The previous5 and present results should open the way to the
Based on the results, we examined the efficiency of 2 (generated
from NaBH4) in ketone reduction by comparison with reduction
by NaBH4 in DMSO–H2O (9:1, v/v) at 25 uC, where acetophenone,
a- and b-acetonaphthones and b-ionone were used as
substrates. The results demonstrated (1) that 2 is more
reduction of other triple, double and single bonds.
Financial support from the Japan Society for the Promotion of
Science (RFTF) and the Ministry of Education, Culture, Sports,
Science, and Technology, Japan is gratefully acknowledged.
efficient (several times) than NaBH4, and (2) that
2
functions as a catalyst.11 We investigated the effect of
additive on c-cyclodextrin-bicapped C60 (1)-mediated reduc-
tion of acetophenone with NaBH4 at 25 uC (or 50 uC) for
1 h. The results are summarized in Table 1. From the
Table 1, the catalytic effect of 2 is evident. Although the
additives (Entries 6, 7, 9 and 10) other than (MeS)3CH
(Entry 11) enhance the turn over frequency (TOF), it is
noteworthy that the dramatic increase in TOF is observed
when excess (Me2N)2CH2–EtONa (Entry 7) is added.
Although a detailed mechanistic study would be necessary
to elucidate the reason why additives, in particular,
(Me2N)2CH2–EtONa effectively increase TOF, it seems due
to the effective regeneration of 2 by NaBH4–(Me2N)2CH2–
EtONa. We have observed that a decrease in absorbance
(lmax 950 nm) of 2 is accompanied by an increase in
Shin-ichi Takekuma, Hideko Takekuma and Zen-ichi Yoshida*
Department of Applied Chemistry, Faculty of Science and Engineering,
Kinki University, 3-4-1, Kowakae, Higashi-Osaka, 577-8502, Japan.
E-mail: yoshida@chem.kindai.ac.jp; Fax: +81-6-6727-4301;
Tel: +81-6-6730-5880 ext. 4020 or +81-6-6721-2332 ext. 4020
Notes and references
1 C. A. Reed and R. D. Bolskar, Chem. Rev., 2000, 100, 1075.
2 (a) G. Schick, M. Levitus, L. Kvetko, B. A. Johnson, J. I. Lamparth,
R. Lunkwitz, B. Ma, S. I. Khan, M. A. Garcia-Garibay and Y. Rubin,
J. Am. Chem. Soc., 1999, 121, 3246; (b) K. Hutchison, J. Gao, G. Schick,
Y. Rubin and F. Wudl, J. Am. Chem. Soc., 1999, 121, 5611; (c)
E. Nakamura and H. Isobe, Acc. Chem. Res., 2003, 36, 807; (d)
Y. Murata, M. Murata and K. Komatsu, J. Am. Chem. Soc., 2003, 125,
7152.
3 (a) H. Tokuyama and E. Nakamura, J. Org. Chem., 1994, 59, 1135; (b)
M. Orfanopoulos and S. Kambourakis, Tetrahedron Lett., 1994, 35,
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Chem. Commun., 2005, 1628–1630 | 1629