Synthetic studies on terpenoids. Part 7. Synthetic studies leading to the total synthesis of eudesmane sesquiterpenes

Abstract

The synthesis of two naturally occurring sesquiterpenes, (±)-junenol (1) and (±)-acolamone (2), from the bicyclic ketone (3) is described. The introduction of an isopropyl chain at C-7 of the bicyclic ketone was attempted by three different procedures and yielded ketone (5) which, on reduction with sodium and ethanol, gave the alcohol (12). This, on oxidation with lead tetra-acetate and iodine in cyclohexane, yielded the cyclic ether (13) and regenerated the ketone (5). Oxidation of compound (13) with chromium(VI) oxide in acetic acid afforded the keto-acid (15) which, on oxidative decarboxylation with lead tetra-acetate, furnished acolamone which was reduced with sodium borohydride in ethanol to (±)-junenol.