Highly Selective Formation of a .beta.-C-Glucosidic Bond in the Reactions of ArSCl-Glucal Adducts with Silicon-Containing Nucleophiles

2-(Arylthio)-2-deoxyglucosyl chlorides, which are easily prepared as a mixture of stereoisomers upon the Ad(E) reaction of ArSCl with tri-O-benzyl-D-glucal, upon treatment with a Lewis acid catalyst can be transformed into cationoid intermediates, presumably episulfonium ions. The latter were shown to be efficient electrophiles capable of alkylating various Si-containing nucleophiles such as TMSCN, allyltrimethylsilane, TMS; enol ethers, and ketene acetals with formation of the corresponding. 2-deoxy-2-(arylthio)-C-glucosides in-preparatively acceptable yields. The final outcome of the reaction corresponds to a net trans-addition of ArS and carbon nucleophile moieties across the double bond of the starting glucal. The stereofacial selectivity of this addition is sensitive to variations in the reaction conditions but generally a below-plane attack is preferable. A highly selective formation of the beta-C-glucosidic bond (ratio of beta-gluco:alpha-manno isomers up to 19:1) can be achieved if the coupling is carried out in CH2Cl2 solution. Thus, the reaction might serve as a convenient method for the synthesis of diverse 2-deoxy-2-(arylthio)-beta-C-glucosides containing aliphatic, cycloaliphatic, or aromatic residues and functional groups like carbonyl, carboxyl, or the double bond.