Synthesis of propargyl C-glycosides using allenyltributylstannane

Protected propargyl C-glycosides have been prepared by activation of the anomeric centres of 2,3,4,6-tetra-O-benzyl- derivatives of d-glucose and d-galactose, followed by treatment with allenyltributylstannane in the presence of Lewis-acid. Activation was by formation of the anomeric acetates, trichloroacetimidates or fluorides; boron trifluoride etherate and trimethylsilyl trifluoromethanesulfonate were particularly effective Lewis-acids. Attempts to perform similar reactions on 1,2,3,4,6-penta-O-acetyl-d-glucose led to participation by the C-2 acetate group and formation of 3,4,6-tri-O-acetyl-1,2-O-[1-(prop-2-ynyl)ethylidene]-α-d-glucopyranose.