Chemistry Letters 2001
1195
Chem. Soc., 119, 994 (1997). b) K. Mizuno, N. Ichinose,
and Y. Otsuji, J. Org. Chem., 57, 1855 (1992).
2
a) M. Abe and A. Oku, J. Chem. Soc., Chem. Commun.,
1994, 1673. b) M. Abe and A. Oku, J. Org. Chem., 60,
3065 (1995). c) A. Oku, T. Miki, M. Abe, M. Ohira, and T.
Kamada, Bull. Chem. Soc. Jpn., 72, 511 (1999).
3
4
A. Oku, H. Takahashi, and S. M. Asmus, J. Am. Chem.
Soc., 122, 7388 (2000).
a) K. Mizuno, M. Ikeda, and Y. Otsuji, Tetrahedron Lett.,
26, 461 (1985). b) K. Mizuno, M. Ikeda, and Y. Otsuji,
Chem. Lett., 1988, 1507.
5
All geometries were optimised and characterized as real
minima (via second derivative calculation) using Becke’s
hybrid density functional B3LYP method with the 6-
311+G(d,p) or 6-31G(d) basis sets. The orbital energies
were taken from a SCF-population analysis on the HF/6-
311++G(3df,2p) level of theory. All calculations were car-
ried out using the GAUSSIAN98 package of programs.15
Relative HOMO energies of substituted cyclopropanes vs
parents cyclopropane are [eV]: 0.475 for 1-H3SiO-, 0.846
for 1-H3SiCH2-, 1.079 for 1,1-(H3SiCH2)2-, 1.338 for (E)-
1,2-(H3SiCH2)2-cyclopropane.
Indeed, the photo-induced electron-transfer reaction (PET) of 3
with carbonyl compounds (Scheme 2, eq 2) enabled the bonding
with allylsilyl or homoallyl moieties (Scheme 1). Thus, the PET
reaction of 3 with benzophenone (13a) in the presence of Mg(II)
salt11 produced C–C bonded product 14 (18%) though in low
yield. To improve the yield, pyrene (0.1 equiv) which has been
known as a redox photocatalyst in PET reactions12 was added.
Consequently, the yield was improved (37%) together with the
increase in the yield of radical homodimer 16 (28%) of radical 5.
Hence, pyrene13 was used in every experiment thereafter.
Under the high dilution conditions, however, expected
improvement in the yield of 1414 was not observed. This indi-
cates that an initially formed radical ion pair in a cage [4 + ketyl
radical] may spontaneously collapse in a polar solvent to stabi-
lized solvent-separated radical ion pair [4] + [ketyl radical],
which, after the removal of silyl cation, finally undergoes the
coupling to give 14, 15 and 16 (Scheme 1). Therefore, product
ratios are more or less statistically controlled and not influenced
by the substrate concentration.
6
a) H. E. Simmons, T. L. Cairns, S. A. Valduchick, and C.
M. Hoiness, Org. React., 20, 1 (1972). b) S. E. Denmark
and J. P. Edwards, J. Org. Chem., 56, 6974 (1991).
T. Shioiri, T. Aoyama, and S. Mori, Org. Synth., 68, 1
(1989).
Similarly, 3 reacted with TCNE under non-irradiated con-
ditions to afford a five-membered [2+3]cycloadduct.
Sequential profile of the reaction was difficult to be proven
by the stereochemical analysis of the adduct.
7
8
9
Similar types of C–O and C–C bonded intermediates were
reported for the reaction of 1 (ref 2b).
10 Review: S. Danishefsky, Acc. Chem. Res., 14, 400 (1981).
11 Formation of complexes between excited carbonyl com-
pounds and Mg salts is reported to retard the back-electron
transfer (see refs 2b and 4).
The effect of Mg2+ is clear. With increase in the molar
equivalence of Mg2+ from 1 to 1.5, the yield of 14 increased
from 3 to 47%. This indicates that the concentration of
homoallyl radical 5 increases in parallel to that of ketyl radi-
cal–Mg2+ complex. The role of pyrene as a photocatalyst is
also evidenced. It functions as a redox catalyst to generate radi-
cal ion 4 (or radical 5) and the ketyl radical. Acetylbenzonitrile
(13b), diacetylbenzene (13c), N-methylphthalimide (13d), and
benzalacetone (13e) also underwent the similar C–C bond
forming reactions with 3 via the PET process. To be noted is
that these ketones reacted with 3 as effectively as benzophe-
none (13a) leading to the C–C bonded products.
In conclusion, the present study has unveiled that TMSCH2
group on a cyclopropane ring plays a role of endowing the ring
with donor character at both ground state and excited state reac-
tions, the effect being comparable to, or even more than that of
TMSO as predicted on theoretical basis. Further study on both
theoretical and experimental bases will widen the versatile pro-
file of the TMSCH2 group.
12 (a) C. Pac, A. Nakasone, and H. Sakurai, J. Am. Chem.
Soc.,99, 5806 (1977). (b) C. Pac and H. Sakurai, Yuki
Gosei Kagaku Kyokaishi, 41, 667 (1983).
13 Among aromatic hydrocarbons examined, pyrene was most
effective in comparison with phenanthrene and anthracene.
14 High dilution was effective in the PET reaction of 2 with
ketones (ref 3).
15 Gaussian 98, Revision A.5, M. J. Frisch, G. W. Trucks, H.
B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman,
V. G. Zakrzewski, J. A. Montgomery, Jr., R. E. Stratmann,
J. C. Burant, S. Dapprich, J. M. Millam, A. D. Daniels, K.
N. Kudin, M. C. Strain, O. Farkas, J. Tomasi, V. Barone,
M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo,
S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala, Q.
Cui, K. Morokuma, D. K. Malick, A. D. Rabuck, K.
Raghavachari, J. B. Foresman, J. Cioslowski, J. V. Ortiz,
B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I.
Komaromi, R. Gomperts, R. L. Martin, D. J. Fox, T. Keith,
M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C.
Gonzalez, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, J. L. Andres, C. Gonzalez, M. Head-
Gordon, E. S. Replogle, and J. A. Pople, Gaussian, Inc.,
Pittsburgh PA, 1998.
References and Notes
1
For example, see a) J. P. Dinnocenzo, H. Zuilhof, D. R.
Lieberman, T. R. Simpson, and M. W. McKeckney, J. Am.