Sodium hydride (0.494 g, 12.3 mmol) was added to a stirred solution of 1-tritylpyrimidine-2,4(1H,3H)-dione (1.75 g, 4.9 mmol) in dry THF (75 mL) at RT. After stirring the mixture at RT for 45 min, 2,4,6-triisopropylbenzene-1-sulfonyl chloride (2.99 g, 9.9 mmol) was added and stirring continued at RT for 2 h. The reaction mixture was poured into a stirred mixture of EtOAc and saturated ammonium chloride solution. The organic layer was dried (MgSO4), concentrated and the residue was subjected to flash chromatography (silica gel/hexane-EtOAc 100:0 to 0:100 gradient) to afford 2-oxo-1-trityl-1,2-dihydropyrimidin-4-yl 2,4,6-triisopropylbenzenesulfonate 4A (1.6 g, 52% yield) as a white solid.
