Cannabinoid studies. IV. Stereoselective and regiospecific syntheses of (±)-Δ9-trans- and (±)-Δ9-cis-6a, 10a-Tetrahydrocannabinol

Abstract

Efficient syntheses of the title compounds are achieved through the intermediate alcohols (13) and (15), prepared by reaction of citral (10) with the lithiated olivetol dimethyl and di(methoxymethy1) ethers (4) and (6). Reaction of the alcohol (13) with boron tribromide yields (�)-∆9-trans-6a,10a- tetrahydrocannabinol (1) after regiospecific dehydrobromination of its hydrogen bromide adduct, whilst treatment of the alcohol (15) with trimethylsilyl bromide affords (�)-∆9-cis-6a,10a-tetra-hydrocannabinol(11). The complementary stereoselectivity of these reactions may provide insight into the nature of cannabinoid cyclization processes.