2-Substituted and 1,2-disubstituted indoles react with m-chloroperbenzoic a
cid and hydrogen peroxide in the presence of acid or calcium chloride affor
ding 2- and 3-(3-oxoindol-2-yl)indoles; whereas 2,3-disubstituted indoles,
reacting with the same oxidants, lead to the formation of products typical
of pentaatomic ring opening. The reaction mechanisms are discussed in terms
of electron transfer processes based on the redox potentials of the reagen
ts, the Marcus theory and the reaction products distribution. The reactions
of 1-hydroxy-2-phenylindole, which yield 2-phenylisatogen (2-phenyl-3-oxo-
3H-indole 1-oxide), bisnitrone and 3-(3-oxoindol-2-yl)indole are also expla
ined by an electron transfer mechanism depending on the oxidant and on the
conditions of the reaction, The structures of 2- and 3-(3-oxoindol-2-yl)ind
oles have been elucidated by X-ray analysis.