Asymmetric Total Synthesis of (+)-6-epi-Castanospermine by the Stereoselective Formation of a syn,anti Acetylenic 2-Amino-1,3-diol Stereotriad

The asymmetric total synthesis of (+)-6-epi-castanospermine (1) is described herein. In this synthesis the diastereoselective addition of a racemic allenylzinc reagent to an enantiopure α-alkoxy-tert-butylsulfinylimine is the key step and is followed by the formation of a piperidine ring by ring-closing metathesis and subsequent syn-dihydroxylation of an alkene.