Tetrasubstituted C-Glycosylidenes and C-Glycosyl Compounds from Di- and Monobromo-Substituted exo-Glycals

Efficient methods for functionalization of readily available exo-glycals have been developed. Sequential palladium-catalysed cross-coupling of dibromo-substituted exo-glycals was first explored and allowed the formation of new disubstituted exo-glycals as single stereoisomers. Bromination of furano- and pyrano-methoxycarbonyl-exo-glycals led to a new series of monobrominated derivatives. These vinylic bromides were used in carbon-carbon bond formation through palladium-catalysed reactions, leading to a new series of previously unknown exo-glycals. Further chemical manipulation of the methoxycarbonyl functionalities and stereoselective hydrogenation of the exocyclic double bond led to C-glycosyl compounds with high stereocontrol.