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Free keywords:
glycosides; glycosylations; glycosyl phosphites; metal perchlorates; LiClO4-solvent mixtures;
Abstract:
Glycosyl phosphites 1-3 derived from glucose are activated under neutral conditions and without the addition of any further promoter in 1 M solutions of LiClO4, Mg(ClO4)(2) or Ba(ClO4)(2) in ether, CH2Cl2, or CH3CN and react under these conditions with the alcohols 5-9 to give the glycosides 10-14. The best results are obtained in the presence of Ba(ClO4)(2). In CH2Cl2 and ether the alpha-anomers predominate, in CH3CN the beta-isomers are formed in excess. Whereas the methyl phosphite 1 and the benzyl phosphite 3 deliver the desired glycosides in yields of 35-66%, the ethyl phosphite 2 is a more reactive glycosyl donor, giving the glycosides 10, 11 and 13 in 62-95% yield.
