Study of the Fischer cyclization of diarylhydrazones and related secondary hydrazones I. Relative orienting capacity of the p-methyl and p-methoxy groups of diarylhydrazines

Abstract

A mixture of isomeric N-arylindoles is formed in the Fischer cyclization of N,N-diphenyllydrazones variously substituted in the para position by CH3 or CH3O groups. The intramolecular competition method makes it possible to form a judgment regarding the relative orienting capacity of the substituents in the aromatic ring in the step involving rearrangement of the enamine form of the hydrazone; in this case the effect of the rate of protonation and tautomerization of the hydrazone is excluded. It was established that the rate of rearrangement increases for the para substituents in the order H< CH3< CH3O.