[N+:1]([C:4]1[CH:5]=[CH:6][C:7]([C:10]([OH:12])=[O:11])=[N:8][CH:9]=1)([O-:3])=[O:2].OS(O)(=O)=O.[CH3:18][CH2:19]O>CCOC(C)=O.C([O-])(O)=O.[Na+]>[CH2:18]([O:11][C:10]([C:7]1[CH:6]=[CH:5][C:4]([N+:1]([O-:3])=[O:2])=[CH:9][N:8]=1)=[O:12])[CH3:19]A mixture of 5-nitro-pyridine-2-carboxylic acid (Step 39.5) (5.74 g, 34.2 mmol), H2SO4 (1 mL) and EtOH (50 mL) was stirred for 1.5 h at reflux. The residue was diluted with EtOAc and saturated solution of NaHCO3. The aqueous layer was separated and extracted with EtOAc. The organic phase was washed with H2O and brine, dried (Na2SO4), filtered and concentrated to afford 6.1 g of the title compound as a white solid: ES-MS: 197.1 [M+H]+; tR=3.22 min (System 1).
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