Regioselective C3-Formylation of 2H-Indazoles Using Selectfluor under Microwave-Assisted Conditions

An efficient microwave-assisted Selectfluor-mediated regioselective C3-formylation of 2H-indazoles bearing a variety of alkyl and aryl substituents using DMSO as the formylating agent has been developed. This methodology provides access to 3-formyl 2H-indazoles with moderate to excellent yields. These functionalized indazoles are potentially useful as templates for drug discovery. Control experimental results suggest that this formylation probably proceeds through a radical pathway.