Copper sulfate pentahydrate (0.08 g; 0.33 mmol; 0.06 eq.) was added to a solution of tert-butyl-3-ethynyl-5-methyl-1H-indazole-1-carboxylate (1.55 g; 6.03 mmol; 1.0 eq.), methyl 4-azidobenzoate (prepared as described in JOC (2006), 71(15), 5822-5825; 1.20 g; 6.77 mmol; 1.1 eq.) and D-(−)-isoascorbic acid sodium salt (0.24 g; 1.22 mmol; 0.20 eq.) in DMF (15 mL) and water (0.50 mL). The reaction suspension was heated in MW at 80° C. for 45 min then poured into HCl (0.1 N solution) and extracted with EtOAc. Combined organic phases were washed with brine, dried over magnesium sulfate, filtered and concentrated. The crude was purified by flash chromatography on silica (n-heptane/EtOAc, gradient from 90:10 to 60:40) to give the title compound as a yellow solid. 1H NMR (300 MHz, DMSO) δ 9.66 (s, 1H), 8.35-8.25 (m, 3H), 8.20 (d, J=8.8 Hz, 2H), 8.05 (d, J=8.7 Hz, 1H), 7.54 (dd, J=1.5, 8.7 Hz, 1H), 3.91 (s, 3H), 2.53 (s, 3H), 1.69 (s, 9H). HPLC (Condition A): Rt 5.07 min (purity 96.8%). MS (ESI+): 434.4.
