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RESEARCH PRODUCT

3.13 Carbohydrate Derived Auxiliaries: Amino Sugar and Glycosylamine Auxiliaries

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The stereodifferentiating potential of carbohydrate auxiliaries is illustrated by examples of oxazolidinones derived from amino sugars and aldimines of glycosylamines. Taking advantage of the bicyclic structure of amino sugar-derived oxazolidinones, reactions of their unsaturated or deprotonated N -acyl derivatives show an efficient exo - versus endo -differentiation. High diastereoselectivity is achieved in the syntheses of β -branched or α -substituted carboxylic acid derivatives. Imines of glycosylamines, in particular of 2,3,4,6-tetra- O -pivaloyl- β - d -galactopyranosylamine, are characterized by a conformation stabilized through the exo -anomeric effect and by their ability to coordinate Lewis acids. This results in the shielding of one of the diastereotopic imine faces. Numerous reactions of nucleophiles with N -glycosyl imines proceed with high diastereoselectivity, for example, Strecker and Ugi reactions, cycloaddition reactions, Mannich reactions, or aza-Sakurai reactions. Using these stereoselective CC-bond-forming processes and the influence of the carbohydrate auxiliaries on stereoselective protonation as well as regioselective deprotonation reactions, enantiomerically pure piperidine alkaloids were synthesized. In addition, amino sugar ligands and glycosylamine derivatives have been demonstrated to be very efficient ligands and organocatalysts in enantioselective catalysis.