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.

•Synthesis of pyranoid glycals using Zn/NH4Cl system.•High yields and short reaction time.•Simple operation and broad functional group compatibility.•Efficient synthesis of glucal in gram-scale amount.A simple and efficient procedure was designed for the preparation of pyranoid glycals. In a novel fashion, a series of protected glycopyranosyl bromides underwent reductive elimination in the presence of zinc dust and ammonium chloride in CH3CN at 30–60 °C. The corresponding glycals were obtained with excellent isolated yields (72–96%) in a short time (20–50 min). Furthermore, the transformation was compatible with different protection patterns and conveniently scalable (86% for 45 g acetobromoglucose) which made it very applicable in organic synthesis.

Commercially available zinc dust in the presence of ammonium chloride in acetonitrile at reflux removes the 2,2,2-trichloroethyl (TCE) group at anomeric centers with excellent yields (>95%) in short reaction times. This present method is easily implemented on substrates containing acyl and benzyl groups and large-scale reactions also proceed in high yield.

Sulfuric acid immobilized on silica gel is designed as a very useful catalyst for synthesis of 2,3-unsaturated glycopyranosides. This handy, metal-free, environment friendly transformation provides high yields and α-stereoselectivities in a very few amount (<0.02 eq.) of catalyst and in short reaction times (<10 min).