Stereoselective C-alkynylation, allenylation, and prop-2-ynylation leading to sugar glycosides

Carbohydrates have been recognized and utilized for a long time as the starting materials for target-oriented syntheses toward optically active compounds. C-Glycosides are often employed for this purpose because they have much potential for the introduction of new stereogenic centers to the side chain. We describe herein various methods for the introduction of carbon chains to the sugar rings under acidic conditions, particularly in the form of alkynyl, allenyl, or prop-2-ynyl group at the anomeric position with high stereoselectivity.