Total synthesis of various elemanolides

Starting with a suitable substituted divinyl cyclohexanone, eleven naturally occurring 12.8-elemanolides bearing exo-methylene or methyl groups at C-11 and differing in substitution as well as in relative configuration, have been synthesized in racemic form. An approach to elemanolides with additional oxygen functionalities is principally possible by modification of the basic concept. Methods for the oxidative generation of terpenoid exo-methylene lactone and furan units are exemplified by synthesis of menthofuran and the p-menthenolides from isopulegols.