Synthesis of α-2-deoxyglycosides by acid-mediated conjugate addition

A new method for the synthesis of alpha-2-deoxyglycosides from hex-1-en-3-uloses is reported. Several acids were surveyed for their ability to mediate the conjugate addition of cyclohexanol to a glucal derived alpha,beta-unsaturated ketone. Although several acids successfully afforded the alpha-2-deoxy-3-uloside as a single anomer, Ph3P (.) HBr in benzene afforded the highest yield of product. These conditions were then applied to other alcohol nucleophiles, and it was found that nonsterically hindered alcohols readily undergo conjugate addition. Finally, the stereoselectivity of reduction of the resulting alpha-2-deoxy-3-uloside was determined for several hydride-reducing agents.