Transition metal catalyzed neoglycoconjugate syntheses*

Carbohydrate-containing clusters of various valency were synthesized using transition metal-catalyzed reactions. Thus, Grubbs’ ruthenium benzylidene catalyst was used successfully in olefin self-and cross-metathesis reactions from both O-and C-alkenyl glycopyranosides. The reaction was also used to generate C-linked pseudodisaccharides. Oxidative dimerization of terminal alkynes such as 2-propynyl glycopyranosides was accomplished with palladium and copper-catalyzed homo-and cross-coupling reactions. Sonogashira-type cross coupling between 2-propynyl and 4-iodophenyl mannopyranosides afforded novel sugar-rods useful in studying carbohydrate–protein interactions. Cyclotrimerization of terminal as well as symmetrical alkyne derivatives with dicobalt octacarbonyl allowed access to trimers and hexamers, respectively.