Synthesis
General procedure for the synthesis of 4-chloro-1H-indazol-3-amine from 2-chloro-6-fluorobenzonitrile: To a solution of 2-chloro-6-fluorobenzonitrile (3 g, 19 mmol) in anhydrous ethanol (50 mL) was added hydrazine hydrate (3.74 mL, 77 mmol). The reaction mixture was heated to reflux at 90 °C for 3.5 h under nitrogen protection. Upon completion of the reaction, it was cooled to room temperature, acetone (20 mL) was added and allowed to stand for 19 hours. Subsequently, the mixture was concentrated under reduced pressure to give an orange to brown solid. The solid was extracted by partitioning between saturated aqueous sodium bicarbonate and dichloromethane. The organic layer was filtered through hydrophobic glass material and concentrated under reduced pressure to give a brown solid. This solid was adsorbed through Florisil (60-100 mesh), upsampled onto a 100 g silica SPE column, and purified using a Flashmaster II system with a gradient elution of 0-10% methanol in dichloromethane solution for 60 min. Fractions 24-29 were collected and the solvent was removed under reduced pressure to give the title compound 4-chloro-1H-indazol-3-amine as a yellow solid (2.14 g, 66% yield).LCMS (System B) analysis resulted in retention time (RT) = 1.58 min and electrosprayed positive ionization mode (ES+) m/z 168 ([M+H]+).
References
[1] Patent: US2010/216860, 2010, A1. Location in patent: Page/Page column 25
[2] Journal of Medicinal Chemistry, 2013, vol. 56, # 5, p. 1946 - 1960
[3] Journal of Organic Chemistry, 2006, vol. 71, # 21, p. 8166 - 8172
[4] Bioorganic and Medicinal Chemistry, 2011, vol. 19, # 1, p. 321 - 329
