Regioselective Manipulation of Carbohydrate-Hydroxyl Groups (Selective Activation of a Hydroxyl Group by Tin Compounds)

Abstract

The specific hydroxyl groups of glycosides are selectively activated on treatment with dibutyltin oxide or bistributyltin oxide. These activated species were easily transformable to the products by the action of a variety of reagents, thus achieving regioselective manipulations of hydroxyl groups without protecting other hydroxyl groups in the carbohydrate molecule. Such methods of regioselective manipulation of carbohydrate-hydroxyl groups using tin reagents, for acylation, alkylation, thioacylation, sulfonylation, and oxidation, particularly focusing for preparation of thio-sugars, oxo-sugars, and amino-sugars, are discussed. The products obtained thereby are good precursors in the syntheses of modified carbohydrates. For example, mono-tosylates prepared by the regioselective sulfonylation gave branched furanosides through ring contraction reaction after treatment with metalate complexes such as lithium aluminum hydride. Thioacyl derivatives are smoothly convertible to deoxy sugars by deoxygenation with tin hydrides. The cyclic O, O-thionocarbontes formed by thioacylation with thiophosgene gave O-S rearrangement products, O, S-thiolcarbonates, when treated with a catalytic amount of tin hydride; the products are convertible to thio-sugars upon hydrolysis. Treatment of glycosides with bis (tributyltin) oxide followed by bromine gave single mono-oxo glycosides usually in good yields. These are otherwise hardly accessible compounds and were converted to amino-sugars by oximation followed by stereoselective reduction.