A catalytic amount of ammonium sulfate was added to a mixture of 6-chloropurine (0.56 grams, 3.62 mmol) and hexamethyldisilazane (15 mL), and the mixture was refluxed for 3 hours. The solvent was evaporated under reduced pressure, and the residue was co-evaporated with dry toluene (3×10 mL). The white solid residue was dissolved in dry methylene chloride (40 mL) and 1,2-di-O-acetyl-5-O-benzoyl-3-deoxy-ribofuranose, (1.00 g, 3.10 mmol) was added. After 10 minutes of stirring, trimethylsilyl triflate (0.8 mL) was added, and the solution stirred at room temperature for an additional 3 hours. A solution of cold, saturated sodium bicarbonate was added. After 5 minutes stirring, the organic layer was separated and the aqueous solution extracted with methylene chloride (2×30 mL). The organic layers were combined and dried over sodium sulfate, to give (5S,2R,3R)-2-(6-chloropurin-9-yl)-5-(phenylcarbonyloxymethyl)oxolan-3-yl acetate, which was purified by crystallization from methanol. The mother liquor was chromatographed on a Chromatotron, to provide additional product.
