ENANTIOSPECIFIC SYNTHESIS OF (-(1S,2R,6S)-1,2-DIMETHYLBICYCLO[4.3.0]NONAN-8-ONE AND (-)-7-EPIBAKKENOLIDE-A())

Synthesis of the chiral bicyclic ketone mentioned in the title startin g from R-carvone, and its elaboration to 7-epibakkenolide-A is describ ed. Conjugate addition of dimethyl copperlithium to R-carvone followed by alkylation of the intermediate enolate generated the allylated com pound 6, which was transformed into the diketone 12 via a sequence of reactions comprising regiospecific Wacker oxidation, ozonation-Criegee rearrangement as key reactions. Intramolecular aldol condensation fol lowed by catalytic hydrogenation converted the diketone 12 into the bi cyclic ketone (+)-3, the optical antipode of the compound derived from the sesquiterpenes bakkenolide-A and fukinone. A 5-exo-dig radical cy clisation based strategy transformed the bicyclic ketone 3 into chiral 7-epibakkenolide-A. (C) 1998 Elsevier Science Ltd. All rights reserve d.