The total synthesis of dihydrocrinine and related compounds

Abstract

Racemic dihydro-oxocrinine (XVIII) was synthesized from the keto-lactam (X) by a sequence of reactions including the Michael-type cyclization of the αβ-unsaturated keto-lactam (XI) by the use of toluene-p-sulphonic acid. The racemic ketone (XVIII) was resolved into optically active dihydro-oxocrinine (XIX) and dihydro-oxovittatine (XX). The former gave dihydrocrinine (II) or dihydroepicrinine (IV) when reduced by the Meerwein-Ponndorf reaction or by lithium aluminium hydride, respectively. The latter (XX) afforded dihydrovittatine (III) or dihydroepivittatine (V) when similarly reduced.