Stereospecific Furanosylations Catalyzed by Bis-thiourea Hydrogen-Bond Donors.

We report a new method for stereoselective O-furanosylation reactions promoted by a precisely tailored bis-thiourea hydrogen-bond-donor catalyst. Furanosyl donors outfitted with an anomeric dialkylphosphate leaving group undergo substitution with high anomeric selectivity, providing access to the challenging 1,2-cis substitution pattern with a range of alcohol acceptors. A variety of stereochemically distinct, benzyl-protected glycosyl donors were engaged successfully as substrates. Mechanistic studies support a stereospecific mechanism in which rate-determining substitution occurs from a catalyst-donor resting-state complex.