SYNTHESIS AND ABSOLUTE-CONFIGURATION OF THE C-12-TERPENOID DEHYDROGEOSMIN FROM THE FLOWER SCENTS OF REBUTIA-MARSONERI AND DOLICHOTHELE-SPHAERICA (CACTACEAE) - A NEW APPROACH TO BIS-ANGULARLY SUBSTITUTED TRANS-DECALINS

Optically ,4a,5,8,8a-octahydro-4,8a-dimethylnaphthalen-4a-ol ((+)-1; d ehydrogeosmin) is released from flower heads of the two cactaceae Rebu tia marsoneri and Dolichothele sphaerica. The absolute configuration o f (+)-1 is identical with that of the known microbial metabolite geosm in (-)-2. The key reactions of the synthesis of 1 are the kinetically controlled transesterification of the primary alcohol 4 using a lipase from Candida cyclindracea and the stereo- and regiospecific angular a lkylation of a cis-decalin skeleton by a Lewis -acid-assisted ring ope ning of the quaternary epoxy-alcohol 3 with MeMgBr/Cul. The sequence p rovides a new entry into the class of bis-angularly substituted trans -decalins.