A. General procedure for the synthesis of methyl 1-tert-butoxycarbonyl-1H-indazole-6-carboxylate: methyl 1H-indazole-6-carboxylate (502 mg, 2.84 mmol), 4-dimethylaminopyridine (DMAP, 69 mg, 0.57 mmol), and triethylamine (Et3N, 431 mg, 4.26 mmol) were dissolved in tetrahydrofuran (THF) under cooling in an ice bath (THF, 10 mL). Subsequently, di-tert-butyl dicarbonate (Boc2O, 743 mg, 3.41 mmol) was slowly added to this solution. The reaction mixture was stirred overnight at room temperature. After completion of the reaction, the mixture was concentrated and the residue was extracted with ethyl acetate. The organic phases were combined, concentrated and purified by silica gel column chromatography to afford methyl 1-tert-butoxycarbonyl-1H-indazole-6-carboxylate (797 mg, 100% yield). The product was characterized by 1H NMR (400 MHz, CDCl3): δ 1.74 (9H, s), 3.97 (3H, s), 7.77 (1H, dd, J = 0.4 Hz, J = 8.4 Hz), 7.95 (1H, dd, J = 1.2 Hz, J = 8.4 Hz), 8.21 (1H, d, J = 0.8 Hz), 8.90 (1H s). Mass spectral analysis: calculated value of [M + H]+ (C14H16N2O4) was 277.118 and measured value was 221.
