β-Enolization in α-phenyl-α,α′,α′-trimethylcycloalkanones

Abstract

Ring expansion through β-proton abstraction from α-methyl groups has been observed for the α-phenyl-α,α′,α′,-tri-methyl derivatives of cyclopentanone and cyclohexanone upon treatment with t-BuO−/t-BuOH/185 °C. This contrasts with the lack of rearrangement found for the α,α,α′,α′-tetramethyl derivatives but is analogous to the behavior of some α-phenyl acyclic ketones. However, this process is reversible in the cyclic systems, but irreversible in the acyclic cases. For all of these α-phenyl substituted ketones, rearrangement is in competition with Haller–Bauer type cleavage. In the cyclic systems, a minor process was observed whereby some of the ring-expanded product is reduced to the corresponding secondary alcohol but there was no evidence of rearrangement through γ-enolate formation involving phenyl proton abstraction, which is a minor process in the α-phenyl acyclic systems.