Stereoselective synthesis of protected 3-amino-3,6-dideoxyaminosugars.

New syntheses of densely functionalized protected derivatives of 3-amino-3,6-dideoxyaminosugars have been accomplished in an efficient and straightforward manner. The key step of such approaches involves a highly stereoselective titanium-mediated aldol addition of a chiral α-bromo ketone, easily available from lactate esters, to crotonaldehyde. Further functional group transformations, including a new regioselective Staudinger-aza-Wittig reaction of an azidodiacetate, afford in a few steps and high yield the desired carbohydrates as advanced intermediates capable of participating in subsequent glycosylation reactions.