Potential intermediate, (±)-di-o-acetyl-3α-phenylselanyl-3,3a-dihydro-B-nor-6,7a-secolycorin-5-one for synthesis of the Amaryllidaceae alkaloid lycorine: formal and total syntheses of (±)-lycorine

Abstract

Formal and total syntheses of the Amaryllidaceae alkaloid, (±)-lycorine 1, were achieved by new synthetic routes via(±)-di-o-acetyl-3α-phenylselanyl-3,3a-dihydro-B-nor-6,7a-secolycorin-5-one 32. Namely, stereoselective intramolecular Diels–Alder reaction of triene ester 5 afforded, in good yield, the cis-lactone 6, which was converted into β(stereochemical)-hydroxy-γ-lactam 23. Oxidation of silyl ether 24 with m-chloroperbenzoic acid gave only β-(tert-butyldimethylsiloxy)-α-epoxide 25, the stereostructure of which was determined by its X-ray crystallographic analysis. Payne rearrangement of compound 25 and successive acetylation furnished α(stereochemical)-acetoxy-β(stereochemical)-epoxy γ-lactam 29, which was transformed into (±)-lycorine 1 by construction of the B ring. Formal total synthesis of(±)-lycorine 1 is also described.