Carbohydrates as Chiral Templates: Stereoselective Tandem Mannich‐Michael Reactions for the Synthesis of Piperidine Alkaloids

Abstract

Pure diastereomers in high yields can be obtained by the reaction sequence shown below followed by crystallization or chromatography. The stereochemical course of the reaction is shown for R = n-propyl, p-chlorophenyl, and 2-furyl. Compound 1, R = 3-pyridyl, requires two equivalents of ZnCl2 for catalysis and reacts stereochemically in the opposite fashion. This reaction can be used to obtain enantiomerically pure (S)-coniine and (S)-anabasine .