Synthesis
General procedure for the synthesis of 2-chloro-6-aminobenzothiazole from 2-chloro-6-nitrobenzothiazole: (B) Synthesis of 2-chloro-6-aminobenzothiazole (3) Compound 2 (1.96 g, 9.14 mmol) was dissolved in a solvent mixture of ethanol (150 mL) and purified water (100 mL), and anhydrous tin (II) chloride (20.7 g) was subsequently added to the solution (20.7 g, 91.7 mmol) was added to the solution. Next, a 4.8 mol/L hydrochloric acid solution (20 mL, 96 mmol) was added dropwise to the reaction mixture and the reaction was refluxed at 120 °C. The progress of the reaction was monitored by thin-layer chromatography (unfolding agent: dichloromethane), and after confirming the complete disappearance of the feedstock, the reaction mixture was alkalized with aqueous sodium hydroxide solution. The insoluble precipitate was removed by filtration and the filtrate was subsequently concentrated under reduced pressure. The residue was extracted three times with ethyl acetate, and the combined organic layers were washed with saturated brine, dried over anhydrous sodium sulfate, and finally concentrated under reduced pressure. The resulting crude product was purified by silica gel column chromatography (eluent: ethyl acetate/hexane = 1/1) to afford compound 3 in white solid form (1.02 g, 61% yield).1H-NMR (300 MHz, CDCl3) δ 3.85 (br, 2H), 6.81 (dd, 1H, J = 2.4, 8.7 Hz), 6.99 (d, 1H, J = 2.4 Hz), 7.70 (d, 1H, J = 8.7 Hz). ms (ESI+) m/z 185.0 [M + H]+.
References
[1] Patent: WO2004/37251, 2004, A1. Location in patent: Page/Page column 99; 100
[2] Journal of the American Chemical Society, 2010, vol. 132, # 39, p. 13586 - 13587
[3] Patent: US2007/155806, 2007, A1. Location in patent: Page/Page column 5
[4] Chemistry - An Asian Journal, 2011, vol. 6, # 7, p. 1800 - 1810
[5] Chemical Communications, 2013, vol. 49, # 77, p. 8644 - 8646
