Hydrogen borrowing enabled Cp*Ir(iii)-catalyzed C3 alkylation of indoles and oxindoles

Abstract

An iridium(III) complex bearing a picolinamidato ligand has been developed as an efficient catalyst for the regioselective C3 alkylation of indoles and oxindoles via a borrowing hydrogen (BH) or hydrogen autotransfer strategy. A broad range of aromatic, heteroaromatic, and aliphatic alcohols, including diols, are successfully employed under solvent-free (neat) conditions with low catalyst loading, demonstrating excellent functional group tolerance. Significantly, this protocol combines high regioselectivity, atom economy, and operational simplicity by avoiding preactivated alkylating agents, external oxidants, or reductants, thereby advancing sustainable C–C bond-forming methodologies. The method is scalable and provides straightforward access to structurally diverse and biologically relevant indole and oxindole frameworks, which are prevalent motifs in pharmaceuticals and natural products. Control experiments, deuterium labeling studies, and spectroscopic investigations support a classical borrowing hydrogen mechanism involving Ir–hydride intermediates.