Dienone–phenol rearrangements of bicyclic cyclohexa-2,5-dien-1-ones; kinetic studies of the importance of a multistage mechanism

Abstract

Kinetic measurements allow the relative importance of pathways for dienone–phenol rearrangements of two bicyclic cyclohexadienones to be assessed. For 3,4a-dimethyl-5,6,7,8-tetrahydronaphthalen-2(4aH)-one (1) the rearrangement rates in aqueous sulphuric acids were apportioned to three pathways. For the analogous 1,4a-dimethyltetrahydronaphthalenone (2) the rates were apportioned to two pathways, both of which allow the angular methyl group to migrate to sites meta to the oxygen function. The indirect path for this process, which involves three separate migration steps, is about as fast as the commonly accepted ‘1,2-migration’ of the methyl group. Comparisons are made with the analogous 4a-methyl-, and 4a,8-dimethyl-5,6,7,8-tetrahydronaphthalenones.