Aromatic annulation on the p-menthane monoterpenes: enantiospecific synthesis of the trans and cis isomers of calamenene and 8-hydroxycalamenene

A new enantiospecific route to sesquiterpenes of the calamenene family is described. The synthetic pathway starts from easily available 3-oxygenated-p-menthane monoterpenes and affords the title compounds by a homologation-benzannulation sequence. The trans and cis isomers of the natural compounds calamenene and 8-hydroxycalamenene were obtained in enantiopure form starting from (-)-menthone and (+)-isomenthone, respectively.