Enantioselective total synthesis and absolute configuration of the natural norsesquiterpene 7-demethyl-2-methoxycalamenene by a silane-terminated intramolecular Heck reaction

The total synthesis of the norsesquiterpene 7-demethyl-2-methoxycalamenene (1) by a newly developed enantioselective silane-terminated Heck reaction is described. The Pd-0-catalyzed transformation of the allylsilane 7, obtained from 3-(3-methoxyphenyl)propanol (2) in 7 steps, provides the tetralin 8 in 91 % yield and with 92 % ee in the presence of (R)-BINAP. Transformation of 8 via 14 and 15 gives 1. The absolute configuration of 1 which has previously not been known was deduced from a single-crystal X-ray analysis of 10, obtained from the cyclization product 8 by hydroboration and acylation with camphanic acid chloride.