Approach to 3-aminoindolin-2-ones via oxime ether functionalized carbamoylcyclohexadienes

Abstract

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 beta-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.