Total synthesis of the (+,-)-biotols and approaches to the synthesis of (+,-)-isocomene

he first total syntheses of (;Reduction of the latter with lithium/ammonia gave dimethyl 3-hydroxy-6-oxo-4,4-exo-8-trimethyl-cis-bicyclo (3.3.0) oct-2-ene-1,2-dicarboxylate. Selective reduction of the C-6 carbonyl group of the latter was achieved by its conversion to the enol acetate, reduction of the ketone with sodium borohydride followed by mild hydrolysis. Monodecarbomethoxylation gave methyl exo-6-hydroxy-3-oxo-4,4-exo-8-trimethyl-cis-bicyclo (3.3.0) -1-carboxylate, whose relative stereochemistry was established by X-ray crystallography, which also confirmed that it has an exo C-8 methyl group.;Treatment of the above with lithium acetylide in the presence of cerium(III) chloride and hydration of the resulting acetylenic bond, followed by acetylation and highly selective reductive removal of the C-3 acetoxyl group gave methyl exo-acetoxy-3-(1-oxoethyl)-4,4,exo-8-trimethyl-cis-bicyclo (3.3.0) octane-1-carboxylate. Hydrolysis of this followed by silylation and cyclization gave exo-6-t-butyldimethylsilyloxy-exo-2,6,6-trimethyltricyclo (5.3.1.0;Reduction of the latter with lithium aluminum hydride, followed by oxidation and hydrogenation gave exo-6-t-butyldimethylsilyloxy-exo-2,6,6-trimethyltricyclo- (5.3.1.0;Several approaches to the synthesis of 1,4-dimethyltricyclo (5.2.2.0;Analyses of the...