6-N-Benzoyladenine (11.02 g.; 46.1 mmol) was dried in vacuo overnight. 1,2-Di-O-acetyl-3-O-benzyl-4-C-methanesulfonyloxymethyl-5-O-methanesulfonyl-D-ribofuranose (19.6 g.; 38.4 mmol) (3) was coevaporated in anh. acetonitrile (3×50 mL) and dried in vacuo overnight. 3 was redissolved in anh. 1,2-dichloroethane (stored over molecular sieves) (175 mL), 6-N-Benzoyladenine was added followed by N,O-bistrimethylsilylacetamide (25.1 mL; 101.3 mmol). The mixture was refluxed for 1 h and cooled to rt. TMS-triflate (13.9 mL; 76.8 mmol) was added and the mixture was refluxed for 5h, stirred overnight at rt, refluxed for further 24 h (red-brown solution) and cooled to rt. The solution was poured into an ice-cold saturated aqueous solution of NaHCO3 (200 mL) and stirred for 0.5 h. The precipitate was filtered off, the phases were separated and the organic phase was washed with a saturated aqueous solution. of NaHCO3 (3×150 mL), dried (Na2SO4) and evaporated. Purification by silica gel column chromatography (1-1.5% MeOH in CH2Cl2) gave 4D as a slightly yellow solid in 68% yield (18.0 g.). NMR was consistent with the data reported in an earlier patent.
