Ethyl 2-((tert-butoxycarbonyl)amino)-3-nitrobenzoate

A mixture of ethyl 2-carboxy-3-nitrobenzoate(23.9 g) and thionyl chloride (12 ml) in benzene (150 ml) was heated under reflux for 3 hours. The reaction mixture was concentrated to dryness. The resultant acid chloride (26 g, quantitative) was dissolved in methylene chloride (20 ml). The solution was added dropwise to a mixture of sodium azide (9.75 g) in dimethylformamide(DMF) (20 ml) while stirring vigorously. The reaction mixture was poured into ether-hexane (3:1, 200 ml) and water (250 ml) to separate into two layers. The organic layer was washed with water and then dried, followed by evaporation of the solvent. The residue was dissolved in t-butanol (200 ml), and the solution was heated gradually with stirring, followed by heating under reflux for 2 hours. The reaction mixture was concentrated in vacuo to give an oily product Ethyl 2-((tert-butoxycarbonyl)amino)-3-nitrobenzoate (30 g).