Stereoselective template-directed C-glycosidation. Synthesis of 5-membered oxygen heterocycles via cation-mediated intramolecular cyclization reactions

Abstract Construction of 5-membered oxygen heterocycles by intramolecular template-directed C -glycosidation is described. Alkylation of thioglycoside 5 with enone 6 followed by enol etherification gave cyclization substrates 8 . Compound 8a underwent silver(I) trifluoromethanesulfonate-mediated ring-closure to give a 1.7:1 mixture of 9 α and 9 β; isomer 8s gave an 8.5:1 ratio. Some derivatization reactions of the bicyclic products are described.