Asymmetric synthesis and absolute stereochemistry of the alkaloies araliopsine, isoplatydesmine, and ribalinine. Dual mechanism for a dihydrofuroquinolone–dihydropyranoquinolone rearrangement

Abstract

(+)-Isoplatydesmine (4), (+)-araliopsine (3), and (-)-ribalinine (7) were obtained by asymmetric synthesis, and the absolute stereochemistry of each alkaloid was studied; reduction in optical purity in a rearrangement of dihydrofuro- into dihydropyrano-quinolones is attributed to competing reactions.