Selective Deoxygenation via Regioselective Thioacylation of Non-protected Glycopyranosides by the Dibutyltin Oxide Method

Regioselective thioacylation of some non-protected glycopyranosides (Me α-D-Glc, Me β-D-Glc, Me α-D-Xyl, Me β-D-Xy1) was examined by the dibutyltin oxide method, using phenoxythiocarbonyl chloride as the thioacylating agent. This method gave the mono-thionocarbonates regioselectively in high yields. Acetylation of these thionocarbonates followed by deoxygenation with tributyltin hydride smoothly gave the corresponding deoxy derivatives, except for the primary thionocarbonates. Similar treatment of the pyranosides that have a cis-vicinal glycol (Me α-D-Gal, Me β-D-Gal, Me β-L-Ara, and Ph α-L-Ara) led to the formation of cyclic thionocarbonates, which on acetylation followed by olefination with trimethyl phosphite afforded the unsaturated derivatives in satisfactory yields. On deacetylation and subsequent hydrogenation over platinic oxide, they gave the corresponding dideoxy derivatives quantitatively. The compounds thus prepared were identified by analyses of their proton and carbon-13 nuclear magnetic resonance spectra.