Electronic factors in the C-glycosidation with silylacetylene

Two kinds of electronic factors have been clarified to control the reactivi ty in alkynylation of glycals with silylacetylenes. One is that the reactiv ity of nucleophile silylpropargyl alcohol derivative largely depends on the protecting group. The second factor is found in the similar electrophiles as oxocarbenium intermediates that were generated from glucals or galactals . Diminished reactivity was found with the 4-axial substituents such as ace toxy or methoxy group.