Base-induced Reactions of 2-Substituted 2-Bromodimedones

Abstract The reactions of 2-substituted 2-bromodimedones with various bases were studied. The behavior of the dimedones changed with the base and substituent attached to the dimedones. Treatment of 2-alkyl-2-bromodimedones (1a and 1b) with a weak nucleophilic base such as sodium acetate afforded 2-alkyl-4,4-dimethyl-2-cyclopenten-1-ones (2a and 2b), 2-alkyl-5,5-dimethyl-3-oxo-1-cyclopentene-1-carboxylic acids (3a and 3b), 2-alkyl-5,5-dimethylcyclohexane-1,3-diones (4a and 4b) and carbon monoxide. A similar treatment of 2,2-dibromodimedone (7) with the weak nucleophilic base gave 2,3-dibromo-4,4-dimethyl-2-cyclopenten-1-one (8), 2-bromo-5,5-dimethylcyclohexane-1,3,4-trione (9) and 2-bromodimedone (10). However, the reactions of 1a and 7 with a strong nucleophilic base such as sodium ethoxide gave mainly the open-chain products, ethyl 3,3-dimethyl-5-oxoheptanoate (5a) and diethyl 3,3-dimethylglutarate (11). On treatment of 1a with silver acetate, a debrominative dimerization occurred to produce the dimer 6. The mechanisms of these reactions were discussed.