Synthetic experiments in the eremophilane sesquiterpene group. Synthesis of (±)-7-epi-nootkatone and partial synthesis of valerianol. The structure of nardostachone

Abstract

Although the Robinson annelation of cis-4-isopropenyl-2-methylcyclohexanone with trans-pent-3-en-2-one affords (±)-nootkatone [4βH,5α-eremophila-1(10),11-dien-2-one] in low yield, the major product is (±)-7-epi-nootkatone. The stereochemical composition of the product appears to be very sensitive to the reaction conditions. A partial synthesis of natural (+)-valerianol [4βH,5α-eremophil-1(10)-en-11-ol] from (+)-nootkatone is described. The structure (15) assigned to nardostachone must be revised, since 4βH,5α-eremophila-1(10),8-dien-2-one (15) synthesised unequivocally from natural nootkatone is not identical with the natural material.