Palladium-catalyzed intermolecular asymmetric dearomatizative arylation of indoles and benzofurans.

Abstract

Indoles represent one of the most robust and synthetically versatile classes of heteroaromatic compounds. However, the stereoselective conversion of planar indole rings into three-dimensional indoline skeletons bearing multiple stereogenic centers remains a persistent challenge in organic synthesis. Herein, we describe an intermolecular catalytic asymmetric dearomatization of simple indoles via a palladium-catalyzed three-component cross-coupling reaction. By using readily accessible diazonium salts and aromatic boronic acids as arylative reagents under a ligand-swap strategy, this method enables the efficient construction of 2,3-diarylated indolines. Mechanistic studies reveal that the chiral BiOx ligand governs the highly stereoselective migratory insertion of the aryl-palladium intermediate into the indole's C═C double bond with complete diastereo- and regioselectivity, whereas the achiral fumarate ligand facilitates the reductive elimination step, as corroborated by density functional theory calculations. Furthermore, this protocol is extended to the dearomative diarylation of benzofurans, affording chiral 2,3-dihydrobenzofuran derivatives with high stereocontrol.