The chemistry of thujone. III. Thujone as a chiral synthon for the preparation of sesquiterpenes. Synthesis of (+)-β-cyperone

Abstract

Robinson annelation of thujone (1) with methyl and ethyl vinyl ketones proceeds stereospecifically to afford the tricyclic enones 6 and 4 respectively. Enone 4 was converted to the glycol 13 which on treatment with 48% hydrobromic acid gave (+)-9-bromo-β-cyperone (14). Reduction with triphenyltin hydride yielded (+)-β-cyperone (3). Enone 6 was converted via standard means to the cyclopropyl alcohol 9, a potential precursor of (+)-junenol (10).