Improving the stereoselectivity of one-carbon atom homologation of hexoses at the terminal position

A number of modifications of the original Grignard C1 homologation of hexoses was examined, e.g. reactions of protected hexodialdo-1,5-pyranosides with benzyloxymethyllithium, transmetalation, precomplexation of the aldehydes. Some of the modifications, e.g. benzyloxymethyl Grignard addition in the presence of tert amines showed good to very good stereoselectivity of the heptoside formation.