Stereoselective Route towards 2,5-Disubstituted Piperidine Alkaloids. Synthesis of (+)-Pseudoconhydrine and (±)-epi-Pseudoconhydrine

This paper describes a new general approach towards functionalized piperidine alkaloids, based on the stereo- and regioselective palladium(0)-catalyzed nucleophilic ring-opening of vinyl epoxides by nitrogen nucleophiles. The latter reaction provides access to stereodefined anti and syn aminoalcohol derivatives, 1-benzyloxy-5-(p-toluenesulfonamido)-3-alken-2-ols (5), which were transformed to (+)-pseudoconhydrine (3) and (±)-epi-pseudoconhydrine (9), respectively, via protection (silyl ether), hydrogenation, debenzylation and cyclization. Detosylation–deprotection gave the final products in good yields and high stereoisomeric purity.