New reactions of 2-substituted indoles

Abstract

2-Alkyl (or aryl) indoles react readily with phenylhydrazine in hydrochloric–acetic acid to give o-aminophenylpyrazoles 7, if the 2-substituent is of small or moderate size, or else 3-aminoindoles, if the 2-substituent is sufficiently bulky. The 3-aminoindoles readily undergo oxidative dimerization to indolylidene aminoindoles [Formula: see text] Evidence is provided for the mechanisms of formation of these two kinds of products.