Condensation between 2-chloro-3H-indol-3-one and phenols

Abstract

2-Chloro-3H-indol-3-one condenses with some phenols having only one reactive position to give quinonoid dyes of the type previously described by Friedlaender. Of the two possible tautomeric forms of these dyes, the quinonoid structure is preferred on the basis of u.v. and n.m.r. spectroscopy and the Michael addition reaction with acetone. The ortho-quinonid dyes show intramolecular hydrogen bonding and are decomposed by alkali to give anthranilic acid and a 2-hydroxybenzaldehyde. The aldehyde recovered from this reaction in deuterium oxide has the aldehydic hydrogen atom replaced by deuterium. The para-quinonoid dyes are protonated by strong acids on the quinonoid oxygen atom and reaction with alkali causes opening of the heterocyclic system to give a benzil, which rearranges.