Oxalyl chloride (10 mL) was added dropwise to a stirred solution of imidazo[1,2-a]pyridine-3-carboxylic acid (1) (3 g, 18.5 mmol) in dry dichloromethane (100 mL) and a few drops of DMF. The resulting solution was stirred at room temperature for 5 hours before it was evaporated to dryness and fresh dichloromethane was added to the resulting acid chloride to make a suspension. In a separate flask, tert-butyl 3-amino-4-methylphenylcarbamate (65) (4.5 g, 20.3 mmol) and DIEA (10 mL) was dissolved in dichloromethane (100 mL) and the above acid chloride solution was added slowly. The resulting solution was stirred overnight at room temperature. Saturated NH4Cl was added to the reaction solution and the phases were separated. The organic layer was dried over Na2SO4 and filtered. After evaporation, the residue was purified over silica gel column using hexane and EtOAc to give tert-butyl 3-(imidazo[1,2-a]pyridine-3-carboxamido)-4-methylphenylcarbamate (66) as a slightly yellow solid.
