Abstract
Cyclohexane-1, 3-dicarboxylic anhydrides (IVa-c), prepared from isophthalic acids in several steps, were treated with diethyl magnesiomalonate and triethylamine to give 3-di (ethoxycarbonyl) -acetylcyclohexanecarboxylic acids (Va-c) in good yields. Compounds Va-c were converted into methyl 3-acetylcyclohexanecarboxylates (VIa-c) by decarboxylation and esterification. Cyclization of VIa-c to bicyclo [3.3.1] nonane-2, 4-diones (I) was performed by refluxing a mixture of VI and potassium hydride in xylene. In the case of VIb, two products (Id and Ie) were obtained. Compounds Ic and Ie were hydrolyzed to Ib and Ig, respectively, by treatment with p-toluenesulfonic acid in acetone and phosphorus tribromide. The 7α-hydroxy β-diketone (If) was obtained from Ib-triketal in three steps via reduction of Ib-2, 4-diketal with lithium aluminum hydride. The keto-enol equilibrium of these β-diketones (Ia-f) and 9-substituted bicyclo [3.3.1] -nonane-2, 4-diones (Xa-b) in deuteriochloroform is also described.
