Acetone → 1-(Tert-butoxycarbonyl)-4-[2,6-difluoro-4-(benzyloxycarbonyl)aminophenyl]piperazine

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To a solution of 4-(4-amino-2,6-difluoro-phenyl)-piperazine-1-carboxylic acid tert-butyl ester (Intermediate III) (25 g, 0.08 mol), in 1:1 acetone:water (300 mL) was added sodium bicarbonate (15.1 g, 0.18 mol). The resulting solution was cooled to 0° C. and benzyl chloroformate (40 mL, 0.24 mol, 50% solution in toluene) was added dropwise. The reaction mixture was stirred at r.t. and progress of the reaction was monitored by TLC. On completion, solvent was evaporated under reduced pressure and the residue was dissolved in ethyl acetate (500 mL). The organic layer was washed with water (2×50 mL), brine (100 mL), dried over anhydrous sodium sulphate and concentrated in vacuo. The residue was purified by column chromatography (silica gel, 2:3 ethyl acetate:Pet. ether) to provide title compound (32 g, 90%) as off white solid.

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