J . Org. Chem. 2001, 66, 2183-2185
2183
Sch em e 1. Rea ction P a th w a ys of Im id oyl
Ra d ica ls
Im id oyl Ra d ica ls a s Syn th on s of Un sta ble
Acyl Ra d ica ls
Shin-ichi Fujiwara,*,† Takahiro Matsuya,‡
Hajime Maeda,‡,1 Tsutomu Shin-ike,†
Nobuaki Kambe,‡ and Noboru Sonoda*,§
Department of Chemistry, Osaka Dental University,
Hirakata, Osaka 573-1121, J apan, Department of Applied
Chemistry, Faculty of Engineering, Osaka University,
Suita, Osaka 565-0871, J apan, and Department of Applied
Chemistry, Faculty of Engineering, Kansai University,
Suita, Osaka 564-8680, J apan
fujiwara@cc.osaka-dent.ac.jp
Received December 4, 2000
imidoyl carbon as exemplified by hydrogen abstraction
with imidoyl radicals to give the corresponding aldimines
(Type 1). A second type is the addition to unsaturated
bonds which have been employed for the synthesis of
various heterocycles3a-c,6e-i,8 as well as natural products.4
The other two reactions are fragmentation of imidoyl
radicals, i.e., R-scission (Type 3) and â-scission (Type 4).
For example, imidoyl radicals 1 having a tert-butyl or
benzyl group on the nitrogen atom are prone to undergo
â-scission, giving nitriles and the corresponding carbon
radicals (R′ ) t-Bu, PhCH2).5 Although R-scission of
imidoyl radicals is much less common than decarbony-
lation of acyl radicals, Nanni et al. reported that an
imidoyl radical possessing a triphenylmethyl group on
the imidoyl carbon atom, derived by hydrogen abstraction
from the corresponding aldimine, underwent R-scission
to afford a triphenylmethyl radical (R ) Ph3C, R′ )
p-MeOC6H4).6i
Imidoyl radicals (RC˙ dNR′, 1), which have the isoelec-
tronic structures of acyl radicals, have been used as
important intermediates in organic synthesis. They can
be generated by the addition of carbon radicals to
isocyanides,2-5 by the abstraction of H, X, SeR, and TeR
groups from aldimines,6 imidoyl halides,7 selenoimidates,8
and telluroimidates,9 respectively, or by thermal decom-
position of appropriate azo compounds.10,11 Reactions of
imidoyl radicals can be classified into four types (Scheme
1). One is the atom2 or group12 transfer reaction onto the
† Osaka Dental University.
‡ Osaka University.
§ Kansai University.
(1) Present address: Department of Applied Chemistry, Graduate
School of Engineering, Osaka Prefecture University, Sakai, Osaka 599-
8531, J apan.
(2) Shono, T.; Kimura, M.; Ito, Y.; Nishida, K.; Oda, R. Bull. Chem.
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Tetrahedron 1995, 51, 9045-9062. (c) Camaggi, C. M.; Leardini, R.;
Nanni, D.; Zanardi, G. Tetrahedron 1998, 54, 5587-5598. (d) Leardini,
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We have developed a variety of transformations based
on the radical carbonylation methodology in which acyl
radicals, formed by reaction of carbon radicals with
carbon monoxide, play important roles as key intermedi-
ates.13 However, this methodology cannot be applied to
a system involving acyl radicals having radical-stabilizing
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10.1021/jo001701h CCC: $20.00 © 2001 American Chemical Society
Published on Web 02/28/2001