Approach Toward Reversal of Chemoselectivity in Catalytic Silylation of Pyranosides

It is widely recognized that primary hydroxy groups show much higher reactivity than the secondary ones, especially in trialkylsilylation. Actually, DMAP-catalyzed silylation of unprotected pyranosides gave the 6-O-silylate exclusively by silylation of the primary C(6)-OH. On the other hand, catalyst ent-C1 overcame the general tendency of silylation, and enabled the selective silylation of the secondary C(3)-OH of two beta-glucopyranosides and a beta-galactopyranoside. Although the yields of the silylation are poor at this stage, this is the first example of selective silylation of the secondary hydroxy group in the presence of the free primary C(6)-OH of pyranosides under the catalyst-controlled conditions.