V. BROMINATED CYCLOALKANONES FROM THE REACTION OF 2.2-DIBROMODIMEDONE WITH SODIUM ACETATE [I] H. DE POOTER(*) and N. SCHAMP By reaction with sodium acetate in hot glacial acetic acid, 2,2-dibromodimedone (VII) is transformed into a mixture of 2-broma-4,4-dimethyl-2-cyclopentenone (IX), 2,3-dibromo-4,4-dimethyl-2-cyclopentenone (X), 3-acetoxy-2-bromo-5,5-dirnethyl-2-cyclohexenone (XI), 2-bromodimedone (VIII), 2,4-dibromodimedone (XIII) and 3-bromo-6,6-dimethyl-1,2,4-cyclohexanetrione (XII). A mechanism is proposed, based on this " acetate reaction " with possible intermediates such as VI11, XIII, 2,2,4-tribromodimedone (XIV) and 2,4,4-tribromodimedone (XV). XIV and XV were prepared in high yield from the easily accessible 2,4-dibromodimedone (XIII) and 2,2,4,4-tetrabromodimedone (XXII).
Methods for the specific synthesis of cyclopentenones IX and X. cyclohexanetrione XI1 and new halogenated dimedones are described.
An earlier publication of this laboratory treated the reactions of 2,2-dichlorodimedone (I) with alcaline reagents [2,3]. It was found that chlorinated dimedones in these reaction circumstances exhibit other properties than those normally attributed to chloroketones. I was transformed into 2-chlorodimedone (11), 2,4-dichlorodimedone (III), 3-chlor0-6,6-dimethyl-1,2,4-cyclohexanetrione (IV), 2-chloro-4,4-dimethy1-2cyclopentenone (V) and 2-chloroxylorcinol (VI) when treated with sodium acetate in boiling glacial acetic acid [3]. As bromoketones generally have properties analogous with those of the corresponding chloroderivatives, but display a greater variety of reactions, it seemed interesting to investigate the behaviour of 2,2-dibromodimedone (VII) [4] towards sodium hydroxide, silver oxide and sodium acetate. Only the reaction with sodium acetate proved promising as VII was completely destroyed by sodium hydroxide, and was converted into 2-bromodimedone (VIII) by silver oxide.
Scope of the reaction
When heating 2,f-dibromodimedone (VII) with a large excess of sodium acetate in glacial acetic acid, a vigorous reaction occurs, under evolution of carbon monoxide, leading to a complex reaction mixture.
The neutral fraction was separated by sublimation into 2-bromo-4,4-dimethyl-2cyclopentenone (IX) and 2,3-dibromo-4,4-dimethyl-2-cyclopentenone (X) [41. If only one or two equivalents of sodium acetate are used, some 3-acetoxy-2-bromo-5,5-dimethyl-2-cyclohexenone (XI) is obtained by destillation of the sublimation residue.