General procedure for the synthesis of 2-methyl-1H-imidazole-5-carboxylic acid from 2-methyl-1H-imidazole-5-carboxaldehyde: To a solution of 2-methyl-1H-imidazole-5-carboxaldehyde (10 g, 91 mmol) in acetonitrile (ACN, 60 mL) was added sulfamic acid (11 g, 120 mmol) at 0 °C and the reaction solution was stirred for 5 min. Subsequently, 2-methyl-2-butene (13 mL, 120 mmol) was added. An aqueous solution of sodium chlorite (11 g, 120 mmol) was slowly added dropwise to the reaction mixture, and after completion of the dropwise addition, the reaction system was brought to room temperature and stirring was continued for 4 hours. After completion of the reaction, acetonitrile (MeCN) was removed by distillation under reduced pressure. The reaction was quenched with 1.5 N hydrochloric acid (HCl) and subsequently extracted with ethyl acetate (EtOAc, 250 mL x 3). The organic phases were combined, washed with brine (200 mL), dried over anhydrous sodium sulfate (Na2SO4), filtered and concentrated under reduced pressure to afford the target product 2-methyl-1H-imidazole-5-carboxylic acid (9.0 g, 71 mmol, 79% yield). The product was characterized by 1H NMR (300 MHz, DMSO-d6): δ 11.94 (brs, 1H), 9.61 (s, 1H), 7.88 (s, 1H), 1.91 (s, 3H).
