2-(Methoxycarbonyl)pyridine-3-carboxylic acid (3 g, 16.57 mmol) was dissolved in 50 mL of tert-butanol and triethylamine (4 mL) was added. After stirring at room temperature for 5 minutes, diphenylphosphoryl azide (3.6 mL, 16.57 mmol) was added and the reaction mixture was refluxed for 3 hours. Upon completion of the reaction, the mixture was concentrated and the residue was purified by fast column chromatography (silica gel) with ethyl acetate/cyclohexane (20% to 50% gradient) as eluent. The fraction containing the target product was collected and concentrated in vacuum to afford methyl 3-{[(tert-butoxy)carbonyl]amino}pyridine-2-carboxylate (1.6 g, 38.5% yield).
