Intermediate formation enabled regioselective access to amide in the Pd-catalyzed reductive aminocarbonylation of olefin with nitroarene

Abstract

An efficient route for the palladium-catalyzed reductive aminocarbonylation of olefins with nitroarenes was developed using carbon monoxide (CO) as both reductant and carbonyl source, which enables facile access to amides with excellent regioselectivity and broad substrate scope. It is found that the counter anions of the Pd catalyst precursors significantly affect the reaction chemoselectivity and amide regioselectivity. Branched amides were mainly obtained with K2PdCl4 as the metal catalyst, and phosphine ligands had no influence on the regioselectivity but affected the catalytic reactivity. However, phosphine ligands had significant effects on aminocarbonylation regioselectivity when Pd(CH3CN)4(OTf)2 was used; monodentate phosphines tended to form branched amides, and bidentate phosphines mainly formed linear amides. Trapping experiments, primary kinetic studies, and control reactions with all possible <I>N</I>-species reduced from nitroarene indicated that the catalytic synthesis of branched and linear amides produced nitrene (further converted to enamide) and aniline, respectively, different from the previous ligand-controlled regioselective synthesis of amides via the aminocarbonylation of olefins with amines. Furthermore, the proposed synthesis route could be applied in the synthesis of gram-scale propanil under mild conditions.