Extended alkenyl glycosides by ruthenium-catalyzed cross-metathesis reaction and application toward novel C-linked pseudodisaccharides

Grubbs's ruthenium benzylidene catalyst (3) has been successfully applied toward the cross-metathesis reactions of allyl alpha-D-galactopyranoside derivative (4) with a number of olefins. Terminal alkenes possessing a wide range of protecting groups were used as cross-metathetic partners to allow syntheses of glycosides having extended spacers and functionality in the aglycon moieties. The reaction is quite general and the cross-metathesis products (14-21) were obtained in high yields. The strategy has also been applied toward the synthesis of some C-linked pseudodisaccharides from allyl alpha-C-galactoside derivatives (23, 26, and 28) in good yields. In almost all cases, trans-stereoselectivity was found to be good to excellent.