Jacob Herzig

Selective deacetylation of anomeric sugar acetates with tin alkoxides

There are three main categories of methods for synthesising glucosides and glucuronides (1 + 2 + 3), namely, (a) the Koenigs-Knorr reaction (1, where Y = halogen) and its modifications2, (6) reactions catalysed by Lewis acids3 (1, Y = OAc), and (c) reactions where HO-1 of the starting derivative is unsubstituted (1, Y = OH). Category (c) includes methods in which HO-1 is initially converted into a more reactive species 4a-g, and those which involve a Lewis acid catalyst’S4h. Direct coupling is attractive since it avoids the preparation of reactive, unstable, and readily hydrolysable derivatives of 1 with Y = Br, OCNHCC&, OCNHNHR, etc. The need for simple methods for the preparation of sugar derivatives with HO-1 unsubstituted is further exemplified by conversions into glycosyl fluorides which are useful in stereoselective glycosidations’. + R3-OH __L1

Methanolysis of acetylated sugars and glycosides in the presence of tin oxides and alkoxides

Abstract A simple, regioselective O -deacetylation procedure is described which involves ⩽0.5 equiv. of Bu 3 SnOMe or Bu 2 SnO in methanol. Anomeric acetates are considerably more reactive than primary and secondary acetates, thereby enabling selective removal, to give ∼70% of products with HO-1 unsubstituted. Prolonged reaction resulted in complete deacetylation. Secondary acetates were removed faster than primary acetates and the overall rates of reaction were influenced greatly by the anomeric substituent in the order of OAc OH ⪢ OMe. No acyl migration took place under the reaction conditions.