Bu4NI-catalyzed, oxidative C(sp2)–C(sp3) cross dehydrogenative coupling for the regioselective direct C-3 benzylation of 2H-indazoles

Abstract

A Bu₄NI-catalyzed, DTBP-promoted, regioselective C_(sp²)–C_(sp³) cross dehydrogenative coupling (CDC) protocol for the direct C-3 benzylation of 2H-indazoles is reported. The metal-free protocol is operationally simple and proceeds mechanistically via the generation of stable benzylic free-radicals followed by regioselective addition at the C-3 position of 2H-indazoles which afforded C-3 benzylated 2H-indazoles up to 87% yields. The methodology showed a varied array of functional group tolerance and wide substrate compatibility. The gram-scale synthesis further highlights the importance and versatile nature of this methodology.