Step 33.3: Synthesis of 3-methylbenzo[d]isoxazol-5-amine
To a stirred solution of 3-methyl-5-nitrobenzo[d]isoxazole (1.8 g, 10.10 mmol) in acetic acid (40 mL) was slowly added a solution of tin(II) chloride dihydrate (6.84 g, 30.3 mmol) in hydrochloric acid (15 mL, 494 mmol). The reaction mixture was stirred at 100 °C for 1 h. After completion of the reaction, the reaction was quenched with saturated aqueous sodium bicarbonate solution. The reaction mixture was diluted with water and extracted with dichloromethane. The organic layers were combined, washed once with saturated aqueous ammonium chloride solution, dried over anhydrous sodium sulfate and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (eluent: hexane/ethyl acetate, 20:50) to afford the title compound (458 mg, 3.09 mmol, 31% yield) as a pink solid. Retention time (t R): 0.50 min (LC-MS 2); electrospray ionization mass spectrometry (ESI-MS): m/z 149 [M + H]+ (LC-MS 2); thin-layer chromatography Rf-value: 0.45 (Expanding agent: hexane/ethyl acetate, 1:1).
