Synthesis
The general procedure for the synthesis of 1H-indazole-6-carbaldehyde from 1H-indazole-6-methanol was as follows: 1H-indazole-6-methanol (278.0 mg, 1.876 mmol) was dissolved in 10.0 mL of dichloromethane (CH2Cl2) and manganese dioxide (MnO2, 816.0 mg, 9.38 mmol) was added. The reaction mixture was stirred at room temperature overnight. After completion of the reaction, the mixture was filtered and the solids were washed with dichloromethane (2 x 25 mL). The combined filtrates were washed sequentially with water and saturated saline and dried over anhydrous magnesium sulfate (MgSO4). After filtration to remove the desiccant, the solvent was evaporated under reduced pressure to give the crude product 1H-indazole-6-carbaldehyde (270 mg, 98% yield) as a white solid. Mass spectrum (electrospray ionization): m/z 147.1 ([M+H]+).
References
[1] Patent: WO2009/54983, 2009, A1. Location in patent: Page/Page column 37-38
[2] Patent: US2008/200535, 2008, A1. Location in patent: Page/Page column 133
[3] Patent: WO2005/44817, 2005, A1. Location in patent: Page/Page column 101-102
[4] Patent: WO2018/177781, 2018, A1. Location in patent: Page/Page column 82; 99-100
