Indoles

In a study of the Fischer cyclization of cyclohexanone mono-p-substituted α, α-diphenylhydrazones (in which the substituents were donor and acceptor groups) it was found that isomeric (formed during cyclization at the substituted and unsubstituted rings) indoles are formed in close ratios. The results were interpreted in terms of sigmatropic processes as a confirmation of the Fischer reaction via a scheme involving a sigmatropic shift.