Short total syntheses of natural glycosides (ellagitannins) were performed through sequential and regioselective functionalization of the hydroxy groups of unprotected glucose. The key reactions are β-selective glycosidation of a gallic acid derivative by using unprotected glucose as a glycosyl donor and catalyst-controlled regioselective introduction of a galloyl group into the inherently less reactive hydroxy group of the glucoside.

Short total syntheses of natural glycosides (ellagitannins) were performed through sequential and regioselective functionalization of the hydroxy groups of unprotected glucose.T he key reactions are b-selective glycosidation of ag allic acid derivative by using unprotected glucose as ag lycosyl donor and catalyst-controlled regioselective introduction of ag alloylg roup into the inherently less reactive hydroxy group of the glucoside. Angewandte Chemie 6275

An S N 2 mechanism was proposed for highly stereoselective glycosylation of benzoic acid with unprotected α-Dglucose under Mitsunobu conditions in dioxane, while an S N 1 mechanism was indicated for nonstereoselective glycosylation in DMF. The S N 2-type stereoselective Mitsunobu glycosylation is generally applicable to various unprotected pyranoses as glycosyl donors in combination with a wide range of acidic glycosyl acceptors such as carboxylic acids, phenols, and imides, retaining its high stereoselectivity (33 examples). Glycosylation of a carboxylic acid with unprotected α-D-mannose proceeded also in an S N 2 manner to directly afford a usually less accessible 1,2-cis-mannoside. One-or two-step total syntheses of five simple natural glycosides were performed using the glycosylation strategy presented here using unprotected α-D-glucose.