Synthesis and reactions of 2-bis(methylthio)methylene-1-methyl-3-oxoindole: a facile access to benzo- and heterocyclo-fused carbazoles and indoles

Abstract

The synthesis and reactions of 2-bis(methylthio)methylene-1-methyl-3-oxoindole 5 as a novel 3-carbon 1,3-bielectrophilic component are described. Thus cycloaromatization of 5 with allyl, methallyl and crotyl Grignard reagents affords substituted carbazoles 12a-c in good yields. Cycloaromatization of 5 with various anions derived from aryl / heteroaryl acetonitriles and antipyrine gives novel benzo[c]- (16), naphtho[1,2-c]- (19), indolo[3,2-a]- (21), thieno[2,3-c]- (23), pyrrolo[2,3-c]- (25) and pyrazolo[4,3-b]- (29) carbazole ring systems in good yields. Similarly heterocyclo[b]-fused indoles like pyrido[3,4-b]- (36), pyrido[3,2-b]- (39) indoles and indolo[3,2-b]quinolizinium salt 42 were synthesized by cyclization of 5 with lithioacetonitrile, lithioaminocrotonitrile, and 2-picolyl lithium respectively via our heteroaromatic annelation protocol.