Regio-and Stereoselective Terminal Allylic Carboxymethylation of gem-Dimethyl Olefins. Synthesis of Biologically Important Linear Degraded Terpenoids

gem-Dimethyl olefins (III) were transformed regiospecifically to the terminal β-methallyl sulfides (IV) bearing the methoxycarbonylmethyl substituent on the sulfur atom via (A) methoxycarbonylmethanesulfenyl chloride addition followed by dehydrochlorination or (B) allylic chlorination with SO2Cl2 followed by sulfenylation with methyl thioglycolate. Treatment of the sulfides (IV) with tert-BuOK or NaH in N, N-dimethylformamide or dimethyl sulfoxide at room temperature gave stereoselectively the sulfur-free esters (V) through a novel one-pot desulfurizative [2, 3]-sigmatropic rearrangement. By utilizing this method, biologically and pharmacologically important linear degraded terpenoids, a diol component (1) of the pheromonal secretion of the queen butterfly and several ω-quinoid acids (4, n=1, 2) and (5, n=1, 2), which are metabolites of polyisoprenoidquinones, were synthesized.