Stereoselective Organocatalytic Fucosylation with Isothioureas

This letter describes a catalytic, α-selective glycosylation of fucosyl chloride donors mediated by a nucleophilic thiourea. This reaction is highly selective in forming both α-fucosyl and α-2-deoxy-2-azido-fucosylated glycosides, including sterically encumbered linkages. Both conformationally flexible and constrained donors participate, giving good to complete α selectivity without the need for directing groups or temperature control. Additionally, we have utilized the parent reaction to access a generalized intermediate for the synthesis of fucosyl lipids.