Step 6a. ethyl 1-methyl-1H-imidazole-2-carboxylate (2.0 g, 13 mmol) was dissolved in 8 mL of concentrated H2SO4, followed by the slow addition of 8 mL of concentrated HNO3. The reaction mixture was stirred at 70 °C for 3 h. The reaction mixture was then extracted with dichloromethane (DCM). After completion of the reaction, the solution was diluted with H2O and the pH was adjusted to 7-8 with aqueous Na2CO3. The reaction mixture was extracted with dichloromethane (DCM) and the organic layers were combined and concentrated. Purification by silica gel column chromatography (eluent: ethyl acetate/petroleum ether) afforded the target compound 1-methyl-5-nitro-1H-imidazole-2-carboxylic acid ethyl ester as a yellow solid (0.9 g, 34.7% yield).ESI-MS m/z = 200.20 [M + H]+.
