Mechanisms of nucleophilic reactions of 4-benzoyl-4-methylcyclohexa-2,5-dienone and its benzoyl substituted derivatives

Abstract

Studies have been made of the reactions with nucleophiles of 4-benzoyl-4-methylcyclohexa-2,5-dienone and its 4-chlorobenzoyl- and 4-methoxybenzoyl- analogues. Water effects hydrolysis to 4-methylphenol and the appropriate substituted benzoic acid. Kinetic measurements give a log k_obsvs. pH profile with slopes close to –1.0, 0, and 1.0, indicating proton, water, and hydroxide ion catalysis, respectively. The results suggest a mechanistic pattern similar to that found for the cleavage of benzaldehyde hemiacetals. Alcohols and alkoxides effect analogous cleavage to 4-methylphenol and the alkyl benzoates. Reaction of the 4-benzoyl-4-methylcyclohexa-2,5-dienone with dialkyl amines gives varying proportions of 4-methylphenyl benzoate and 4-methylphenol with N,N-dialkylbenzamide. An initial amine-induced rearrangement of the dienone to 4-methylphenyl benzoate is followed by cleavage by the amine to give the phenol and amide.