Stereoselective rearrangement of trichloroacetimidates: application to the synthesis of alpha-glycosyl ureas.

A new method for the stereoselective synthesis of alpha-glycosyl ureas, via nickel-catalyzed [1,3]-rearrangement of glycosyl trichloroacetimidates, has been developed. The alpha-stereoselectivity at the anomeric carbon of the resulting trichloroacetamides depends on the nature of the cationic nickel catalyst. This method is applicable to a number of trichloroacetimidate substrates. The alpha-glycosyl trichloroacetamides can be directly converted into alpha-glycosyl ureas in the presence of amines. In all cases, the stereochemical integrity at the urea linkages remains intact.