New Olefinic Cyclizations by Oxymetallation. Conversion of (−)-elemol to (−)-selina-4α, 11-diol (cryptomeridiol) and (−)-guai-1 (10)-ene-4α, 11-diol

Acetoxythallation of (?)-elemol acetate ( 1b ) yields a diacetate 2b which after treatment with lithium aluminium hydride gives (?)-guai-1 (10)-ene-4α, 11-diol ( 2a ). (?)-Elemol ( 1a ) is converted to (?)-selina-4α, 11-diol ( 9 , cryptomeridiol) by hydroxymercuration followed by reductive demercuration. (+)-γg-Elemene ( 5 ) similarly yields (+)-selin-7(11)-en-4α-ol ( 11 , juniper camphor). The stereochemistry and mechanism of these metal salt-induced olefinic cyclization and their biogenetic implication are discussed.