Asymmetric Total Syntheses of (−)-Lycoramine, (−)-Lycoraminone, (−)-Narwedine, and (−)-Galanthamine

Abstract

A concise asymmetric total synthesis of naturally occurring Amaryllidaceae alkaloids sharing dihydrobenzofuran scaffolds, (−)-galanthamine (1a), (−)-lycoramine (1b), (−)-narwedine (2a), and (−)-lycoraminone (2b), is reported. Orthoester Johnson–Claisen rearrangement of allyl alcohol (+)-9 (98% ee) in diisopropylethylamine furnished enantioenriched cyclohexene (+)-8 (97.4% ee) with a quaternary stereogenic center.