The chemistry of thujone .20. New enantioselective syntheses of Ambrox and epi-Ambrox

The development of a new synthetic approach to (-)-Ambrox(R) (37) and epi-Ambrox(R) (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 beta-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(R) (18).