Synthesis of 4-benzoyl-4-methylcyclohexa-2,5-dienone and its benzoyl substituted derivatives: isolated 4-acylcyclohexa-2,5-dienones

Abstract

The syntheses are reported of 4-benzoyl-4-methylcyclohexa-2,5-dienone, and its 4-(4-chlorobenzoyl) and 4-(4-methoxybenzoyl) analogues. These are the first isolated 4-acylcyclohexa-2,5-dienones containing the dienone function in a monocyclic ring system. All are sensitive to nucleophilic attack at the benzoyl carbonyl group, being cleaved to 4-methylphenol and derivatives of the appropriate substituted benzoic acid. Treatment with acids failed to give the desired dienone–phenol rearrangement, with a [1,2] benzoyl migration from C-4 to C-3, but instead gave 4-methylphenyl benzoate or its derivatives, by a reversal of a Fries rearrangement with C-4 to O- aroyl migration.