Synthesis
GENERAL METHOD: Cesium carbonate (12.26 mmol) was added to a tetrahydrofuran (THF; 25 mL) solution of 5-nitroindazole (6.13 mmol) cooled at 0 °C. After stirring for 15 min at 0 °C, iodomethane or allyl bromide (6.13 mmol) was added dropwise. The reaction was monitored by thin layer chromatography (TLC) until the starting material disappeared. Subsequently, the reaction mixture was concentrated by evaporation. The crude product was dissolved in ethyl acetate (EtOAc; 50 mL), washed sequentially with water and brine, and dried over anhydrous magnesium sulfate (MgSO). After removal of the solvent under reduced pressure, the resulting residue was purified by silica gel column chromatography with ethyl acetate/hexane (3:7, v/v) as eluent to afford 1-alkyl-5-nitroindazole and 2-alkyl-5-nitroindazole, respectively.
References
[1] Synthetic Communications, 2015, vol. 45, # 17, p. 2005 - 2013
[2] Tetrahedron, 2008, vol. 64, # 28, p. 6711 - 6723
[3] Patent: US2014/371219, 2014, A1. Location in patent: Paragraph 0659; 0660; 0661
[4] Patent: WO2016/57834, 2016, A1. Location in patent: Paragraph 000406
