Synthesis of Vinca Alkaloids and Related Compounds, 76.1Synthesis and Ring Transformations of Compounds with the Aspidospermane- and D-Noraspidospermane Skeleton. A Formal Synthesis Of (±)-12-Demethoxy-N(1)-Acetyl-Cylindrocarine

Reaction of compound (4) with (5) give a mixture of the isomers (7) and (8) through the intermediate (1). Further conversions led through the oxo- (9), (10) and thioxo (11), (12) derivatives to (±)-19-ethoxycarbonyl-19-demethylvincadifformine (3), and (±)-18-methoxycarbonyl-D(14)-norvincadifformine (13). The preparation of the former compound constitutes the formal synthesis of (±)-12-demethoxy-N(1)-acetylcylindrocarine (2). Oxidative ring transformation of the latter gave (±)-21-methoxycarbony 1-D(18)-norapovincamine (14).