Facile preparation of methyl 5-aryl-4-hydroxyhex-2(E)-enoate, chiral synthon of bisabolane-type sesquiterpenes, based on lipase-catalyzed kinetic resolution and rearrangement of an aryl group

The lipase-catalyzed enantioselective acetylation of racemic methyl (4S∗,5S∗)-4-aryl-5-hydroxyhex-2(E)-enoates 1a-h was performed and efficient resolutions were achieved (E >400) by using CAL-B. After brosylation of the obtained optically active 1a-h, solvolysis of brosylates 13a-h afforded the corresponding methyl (4S∗,5S∗)-5-aryl-4-hydroxyhex-2(E)-enoates 3a-h (26-94% yield). The yields of 3a and 3c on the solvolysis of the corresponding 13 were 92% and 40%, respectively, while solvolysis of the corresponding tosylate was reported at 70% and 17%, respectively. This procedure is a facile and practical route to the synthesis of bioactive and optically active bisabolane-type sesquiterpenes.