The chemistry of thujone. XX. New enantioselective syntheses of Ambrox and epi-Ambrox

Abstract

The development of a new synthetic approach to (-)-Ambrox® (37) and epi-Ambrox® (29) using thujone (1) as a chiral synthon, is presented. Thujone (1), a readily available starting material obtained from Western red cedar, can be efficiently converted to β-cyperone (2) and the latter is then chemically elaborated to the key intermediate, the enone 6. A carbonyl transposition of 6 to enone 9 also allows a formal synthesis of (-)-Polywood® (18).