Synthetic studies on terpenoids. Part 6. Synthesis of (±)-4,13-dimethyl-13-vinylpodocarp-8(14)-en-4α- and -4β-ols

Abstract

The podocarpa-8,11,13-trien-4-one (6) was converted into the corresponding 4-methylpodocarpatrien-4-ol (7) with MeLi. Birch reduction of the alcohol (7) with Li–liquid NH₃ yielded the podocarpenone (8) and the podocarpadienones (9) and (10). Condensation of (8) with ethyl cyanoacetate followed by conjugate addition of Me₂CuLi afforded the 13-cyano(ethoxycarbonyl)methyl ester (12) which on alkaline hydrolysis, esterification and reduction with LiAIH₄ afforded the corresponding 13-hydroxyethyl compound. Conversion of the latter, into its tosylate and elimination of the resulting tosylate by alumina gave 4,13-dimethyl-13-vinylpodocarp-8(14)-en-4β-ol (1). Dehydration of 13-methoxycarbonylmethyl-4,13-dimethylpodocarp-8(14)-en-4-ol furnished the 4-methylene compound (16) which on epoxidation and then reduction with LiAIH₄ produced alcoholic material whose transformation to the tosylate followed by its elimination with alumina yielded the 4,13-dimethyl-13-vinylpodocarp-8(14)-en-4α-ol (2). Hydrolysis of compounds (1) and (2) with PtO₂ in ethanol afforded the corresponding 13-ethyl compounds (3) and (4) respectively.