TMSOTf mediated stereoselective synthesis of α-C-glycosides from unactivated aryl acetylenes.

A metal free and highly stereoselective procedure for the synthesis of 2,3-unsaturated-C-glycosides has been developed between glycals and unactivated aryl acetylenes in the presence of TMSOTf through a triflated C-vinyl glycosides intermediate. The flexibility of the procedure was tested by a wide variety of glycals and unactivated aryl acetylenes (20 examples). The corresponding alkynyl C-glycosides were obtained in good yields with completely α-selectivity in a short time (<25 min). And a plausible mechanism for the synthesis of alkynyl C-glycosides was depicted.