Rhodium(I)-Catalysed Aryl C–H Carboxylation of 2-Arylanilines with CO2

An unprecedented amino-group assisted C–H carboxylation of 2-arylanilines with CO2 under redox-neutral conditions using a Rhodium(I)-catalyst has been developed. This reaction was promoted by a phosphine ligand with t-BuOK as the base and did not require the use of an extra strong organometallic reagent. Notably, this protocol may involve an oxidative addition in the C–H bond cleavage step and is distinct from previous Rh(I) or Rh(II)-catalysed methods for C–H carboxylation with CO2 mechanistically. It enabled an efficient direct conversion of a broad range of 2-(hetero)arylanilines including electron-deficient heteroarenes to various phenanthridinones, which could be further transformed to other synthetically useful compounds readily. Preliminary mechanistic studies were carried out and possible intermediates of the reaction were evaluated, which revealed that the Rh(I)-catalyst is essential for the C–H activation process, providing a promising general type of method for utilization of CO2 for C–C bond formation.