Regioselective [5,5]-sigmatropic rearrangement reactions of aryl hydrazides.

[reaction: see text] N,N'-Aryl hydrazides with substituents at the ortho or meta positions undergo highly regioselective [5,5]-sigmatropic rearrangement reactions to furnish benzidines in good to excellent isolated yields. The presence of single substituent at either the ortho or meta position provides sufficient bias, effectively suppressing the formation of diphenylene, the major byproduct of the conventional benzidine rearrangement reaction.