A Stereoselective Synthesis of α - and β-2′-Deoxy-2-thiouridine

A stereoselective glycosylation procedure is described for the synthesis of protected α- and β-2′-deoxy-2-thiouridine (dS2U) in 68% and 94% yield, respectively. Evidence is presented that suggests the reaction proceeds through a silylated thio-glycoside intermediate. This intermediate undergoes an efficient S2 → N1 rearrangement mediated by SnCl4. The phosphoramidite and phosphodiester synthons and a dS2U dinucleotide are also synthesized and the X-ray structure of β-dS2U is presented.