Stereoselective Template-Directed C-Glycosidation. Synthesis of 5- Membered Oxygen Heterocycles via Cation-Mediated Intramolecular Cyclization Reactions.

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 9α and 9β; isomer 8s gave an 8.5:1 ratio. Some derivatization reactions of the bicyclic products are described.