Approach to 3-Aminoindolin-2-ones via Oxime Ether Functionalized Carbamoylcyclohexadienes

O-Benzyloxime ether substituted amidocyclohexadienes were prepared in three steps in good yields
from 2-aminoacetophenone. EPR spectroscopic observations and product analyses showed that
peroxide-induced decompositions of model compounds led to indolin-2-ones with benzyloxyaminyl
substitution at their 3-positions. The cyclization steps were very rapid and took place regioselectively
at the C-atoms of the CN bonds, by 5-exo ring closures. An O-trityloxime ether analogue was also
prepared. The cyclohexadienyl intermediate smoothly yielded an alkoxylaminyl radical again by
rapid 5-exo-cyclization. However, ring closure was quickly followed by another β-scission step that
released the persistent trityl radical and a 3-nitrosoindolin-2-one derivative. EPR spectroscopic
evidence showed that the nitroso compound trapped other transient intermediates to afford a series
of nitroxides. GC−MS analyses of products formed in reactions including methyl thioglycolate
indicated that 1-benzyl-3-methyl-1,3-dihydro-2H-indol-2-one was derived from the indolinone moiety.