A suspension of sodium 4-(4-pyridyl)benzoate (425 mg, 1.92 mmol) in methylene chloride was treated with oxalyl chloride (0.840 mL, 9.60 mmol), followed by dimethylformamide (0.01 mL). After 0.75 h, the mixture was concentrated in vacuo. The residue was then dissolved in methylene chloride and added dropwise to a solution of N4-(tert-butyloxycarbonyl)-3,4-pyridinediamine (400 mg, 1.92 mmol) and pyridine (0.31 mL) in methylene chloride (2 mL) and tetrahydrofuran (1 mL). After 16 h, the mixture was poured into ethyl acetate and 1 N aqueous sodium hydroxide. The organic layer was washed once with 1 N aqueous sodium hydroxide, once with saturated sodium chloride solution, dried (potassium carbonate), and filtered. The residue was purified by flash chromatography (silica gel, ethyl acetate/hexanes) to yield 75 mg (10%) of the title compound.
