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 pure(+)‐(4 S , 4a S , 8a S )‐1,2,3,4,4a,5,8,8a‐octahydro‐4,8a‐dimethylnaphthalen‐4a‐ol((+)‐ 1 ; dehydrogeosmin) is released from flower heads of the two cactaceae Rebutia marsoneri and Dolichothele spharica . The absolute configuration of (+)‐ 1 is identical with that of the known microbial metabolial geosmin (−)‐ 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 alkylation of a cis ‐decalin skeleton by a Lewis ‐acid‐assisted ring opening of the quaternary epoxy‐alcohol 3 with MeMgBr/Cul. The sequence provides a new entry into the class of bis‐angularly substituted trans ‐decalins.