Wolfrom

We shall describe a specific synthetic example for each protective group given above. Regiosdective proteaion is generally only possible if there are hydroxyl groups of different sterical hindrance (prim < sec < tert equatorial < axial). Acetylation has usually been effected with acetic anhydride. The acetylation of less reactive hydroxyl groups is catalyzed by DMAP (see p.l44f.). Acetates are stable toward oxidation with chromium trioxide in pyridine and have been used, for example, for protection of steroids (H.J.E. Loewenthal, 1959), carbohydrates (M.L. Wolfrom, 1963 J.M. Williams, 1967), and nucleosides (A.M. Micbelson, 1963). The most common deacetylation procedures are ammonolysis with NH in CH OH and methanolysis with KjCO, or sodium methoxide. 

Trifluoroacetamides are more stable toward nucleophiles than the corresponding esters and are easily formed from trifluoroacetic anhydride and the amine. The trifluoroacetyl group (Tfac) is slowly cleaved by aqueous or methanolic HQ, NH, or Ba(OH)2 solutions as well as by NaBHj in methanol (M.L. Wolfrom, 1967). 

R. L. Whisder and M. L. Wolfrom, ed.. Methods in Carbohydrate Chemisty, Vol. Analysis and Preparation of Sugars, Academic Press, New York, 1962. M. Dubois and co-workers, Chem. 28, 350 (1956). 

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