Synthesis and structure of 4-O,6-O-glycosylidene glycosides

Interglycosidic spiro ortho esters (9-20) were efficiently prepared from me thyl 2,6-di-O-benzylgluco-or galactopyranoside and various sugar lactones i n the presence of methoxytrimethylsilane and a catalytic amount of trimethy lsilyl triflate; All of the prepared sugar ortho esters possess perhydrospi ro[2H-pyran-2,2'-pyrano[3,2-d] [1,3]dioxin] ring systems commonly in their molecules and, remarkably, were afforded as single isomers. The configurati ons of the spiro centers in their molecules were determined or estimated by X-ray single crystallographic analysis and molecular modeling studies. By comparing the conformations of prepared ortho esters, we revealed that the difference in the stability between two possible isomers was principally ca used from that between the spiro ring systems in their molecules in each ca se.