Novel access to cyclohexane-1,4-diones and 1,4-hydroquinones via radical 1,2-acyl rearrangement on 2-(halomethyl)cyclopentane-1,3-diones using cobaloxime-mediated electroreduction or tributyltin hydride

A new preparative access to synthetically useful cyclohexane-1,4-diones 2 and their oxidized analogues, hydroquinones 3, with the option of introducing alkyl and aryl substituents, was developed by radical 1.2-acyl rearrangement on 2(halomethyl)cyclopentane-1,3-diones 1, accessible from 1.2-bis(trimethylsiloxy)cyclobutene and alpha-bromo ketone dimethyl acetals. The electroreduction of monoacetals of I in the presence of cobaloxime as a catalyst afforded the cyclohexane-1.4-dione monoacetals in good yields. The Bu3SnH-reduction of 2-aryl I under refluxing in benzene effected the rearrangement, affording 2, and when the reaction was prolonged, aromatization to 3 proceeded in moderate yields. (C) 2002 Elsevier Science Ltd. All rights reserved.