Asymmetric routes toward polyhydroxylated pyrrolidines: Synthesis of 1,4-dideoxy-1,4-imino-d-galactitol and 1,4-dideoxy-1,4-imino-d-glucitol.

Herein the total synthesis of the pyrrolidine alkaloids 1,4-dideoxy-1,4-imino-d-galactitol and its diastereoisomer 1,4-dideoxy-1,4-imino-d-glucitol is described, starting from a common optically active precursor. The key step in our approach was the double diastereoselection in the asymmetric dihydroxylation of chiral vinyl azido alcohols, obtained by means of two different regio- and stereoselective nucleophilic openings of the corresponding chiral vinyl epoxide.