Concise asymmetric total syntheses of (−)-nuciferol, (−)-nuciferal, and (−)-dihydrocurcumene via Rh(I)-catalyzed boronic acid addition

Abstract

A general catalytic asymmetric total synthesis of aromatic bisabolane sesquiterpenes, (−)-nuciferol (ent-1c), (−)-nuciferal (ent-1d), and (−)-dihydrocurcumene (ent-1h) have been achieved in 5–6 steps in high chemical yields from commercially available (E)-ethylcrotonate. A key catalytic enantioselective boronic acid addition onto (E)-crotonate in the presence of Rh(I)-(S)-BINAP afforded enantioenriched product with benzylic stereogenic center in 93% yield with up to >99% ee.