Carbohydrates as Stereodifferentiating Auxiliaries

Carbohydrates are inexpensive natural products. Although they contain numerous functional groups and stereogenic centers in one molecule, carbohydrates were recognized as stereodifferentiating auxiliaries much later than other classes of natural products as for example amino acids or terpenes. Apart from their polyfunctional nature carbohydrates are characterized by the anomeric and exo-anomeric effects which have distinct influence of the spatial orientation of substituents linked to the anomeric position. Based on these stereochemical properties carbohydrates were used as stereodifferentiating auxiliaries in numerous diastereoselective reactions, such as aldol addition, alkylation reactions, conjugate addition, and cycloaddition reactions with dienes, ketenes, or carbenes. Furthermore, dipolar cycloaddition reactions proceeded with high diastereoselectivity affording heterocycles.