Some Aspects of Regio—, Stereo—1 and Chemoselective Reactions in Carbohydrate Chemistry

Selective transformations in carbohydrate chemistry will be illustrated with examples chosen from three distinct areas: 1. Phase transfer reactions are useful in obtaining partially substituted carbohydrate intermediates. The substitution patterns frequently are quite different to those obtained in homogeneous phase. 2. Various reagent systems have been developed for the conversion of hyd roxy compounds to chlorodeoxy b romodeoxy and deoxyiod o compounds as well as to olefinic derivatives. A number of partial substitutions have been achieved starting from unsubstituted hexopyranosides providing easy access to some compounds of biological significance. 3. Benzylidene acetals, phenyl substituted derivatives of these and also 2—propenylidene acetals may be reductively cleaved in the presence of proton or Lewis acids to give partially substituted derivatives useful as intermediates in various synthetic work. The regioselectivity may be manipulated by change in reagent or solvent.