To a solution of 5′-O-(tert-butyldiphenylsilyl)-3′-O-(3-tert-butylphenoxythiocarbonyl)-2′-O-(2-methoxyethyl)-5-methyluridine (15.0 g, 20.0 mmol) in 150 mL of benzene was added PhCH═CHSnBu3 (18.7 g, 50 mmol). The resulting solution was degassed three times with argon at rt and 45° C. After AIBN (1.0 g, 6.1 mmol) was added, the resulting solution was refluxed for 2 h. Another portion of AIBN (1.0 g, 6.1 mmol) was added after cooling to about 40° C. and refluxed for 2 h. This procedure was repeated until the starting material disappeared. The solvent was evaporated and the residue was purified by flash chromatography on a silica gel column using 10:1 and 5:1 hexanes-EtOAc as eluent to give 1.74 g of 5′-O-(tert-butyldiphenylsilyl)-3′-deoxy-2′-O-(2-methoxyethyl)-3′-(2-phenylethenyl)5-methyluridine as a white foam.
