Novel carbohydrate-based mono- and bidentate oligosilyl ethers

Regioselective one-pot O-silylation reactions of 1,2-O-isopropylidene- α-D-glucofuranose and 1,2-O-isopropylidene-β-D-fructopyranose using bulky oligosilyl groups are described. Some new silylating reagents (oligosilyl bistriflates), which were generated in situ from readily available phenylsilanes, resulted in 5,6-O-(glucofuranose) and 4,5-O-bridged (fructopyranose) carbohydrates with favoured seven- and eight-membered rings. In these cyclic oligosilyl diethers, three and four ring atoms, respectively, are Si atoms. It is noteworthy, that the seven-membered ring of 5,6-O-[2,4- bis(trimethylsilyl)-1,1,1,3,3,5,5,5-octamethylpentasilan-2,4-diyl]-1, 2-O-isopropylidene-α-D-glucofuranose was expanded to an eight-membered ring by regioselective insertion of aerial oxygen into one of the Si-Si bonds. X-ray analyses of some derivatives are presented.