Oxidative cross-dehydrogenative coupling (CDC) via C (sp 2 ) -H bond functionalization: tert -butyl peroxybenzoate (TBPB)-promoted regioselective direct C-3 acylation/benzoylation of 2 H -indazoles with aldehydes/benzyl alcohols/styrenes.

An efficient, cost-effective, transition-metal-free, oxidative C (sp 2 ) -H/C (sp 2 ) -H cross-dehydrogenative coupling via a C (sp 2 ) -H bond functionalization protocol for the regioselective direct C-3 acylation/benzoylation of substituted 2 H -Indazoles 1a-m with substituted aldehydes 2a-q/benzyl alcohols 5a-e/styrenes 6a-e is reported. The operationally simple protocol proceeds in the presence of tert -butyl peroxybenzoate (TBPB) as an oxidant in chlorobenzene (PhCl) as a solvent at 110 °C for 24 h under an inert atmosphere, which furnished a diverse variety of substituted 3-(acyl/benzoyl)-2 H -indazoles 3a-q/4a-l in up to 87% yields. The reaction involves a free-radical mechanism and proceeds via the addition of an in situ generated acyl radical (from aldehydes/benzyl alcohols/styrenes) on 2 H -indazoles. The functional group tolerance, broad substrate scope, control/competitive experiments and gram-scale synthesis and its application to the synthesis of anti-inflammatory agent 11 and novel indazole-fused diazepine 13 further signify the versatile nature of the developed methodology.