Efficient stereoselective syntheses of piperidine, pyrrolidine, and indolizidine alkaloids

Recent advances in the diastereo- and enantioselective synthesis: of piperidine, pyrrolidine, and indolizidine alkaloids, based on the highly stereoselective 1,2-addition to the CN double bond of chiral aldehyde-SAMP/RAMP hydrazones, are described. The enantioselective syntheses of the pyrrolidine alkaloids bgugaine and (2S,12'R)-2-(12'-aminotridecyl)-pyrrolidine. a defense alkaloid of the Mexican bean beetle are reported. Furthermore, the SAMP/RAMP-hydrazone method was applied to the syntheses of two 5,8-disubstituted indolizidine alkaloids that have been extracted from neotropical poison-dart frogs. The alpha -alkylation of aldehyde-SAMP/RAMP hydrazones has been used in the enantioselective synthesis of two epimers of stenusine, a 3-substituted piperidine alkaloid and spreading reagent of the beetle Stenus comma.