Convenient access to carbohydrates possessing an exo-methylene group adjacent to the ring oxygen at C-1 can be achieved by direct methylenation of aldonolactones with dicyclopentadienyidimethyltitanium.
TMSOTf-promoted glycosidation of acetate (α)-2 and acetate 7 donors with 1 equiv of primary 3 and secondary 5 sugar alcohols acceptors gave exclusively the corresponding α-d-ketodisaccharides 4a, 8a, 11a, and 12a in 60–73% yield. On the other hand glycosidation of the acetate 6 with the primary alcohol 3 under the above conditions afforded a mixture of α- and β-d-ketodisaccharides 9a and 10a in ca