CO2-Mediated Pd-Catalyzed Stereo- and Regioselective Arylation of Free Allylamines

Mizoroki-Heck couplings are a powerful method for elaborating alkene feedstocks. While selective functionalization of terminal olefins has been achieved by catalyst design, selective functionalization of internal olefins has generally required use of directing groups except in the case of Michael acceptors. Allylamine substrates have typically required protection to be suitable for these reactions, decreasing the step and atom economy of these procedures. Herein we demonstrate that the addition of CO₂ (dry ice) allows for the reproducible stereospecific arylation of both secondary and primary allylamines in the presence of a Pd^II catalyst. Notably, the product 3,3’-diarylallylamine motif is prevalent in a variety of biologically-relevant structures, and this method represents the most straightforward synthesis of these targets to date. Key features of the method are the ability to access relatively mild conditions that facilitate a broad substrate scope, as well as direct diarylation of terminal allylamine substrates. In addition, several complex and therapeutically-relevant molecules are included to demonstrate the utility of the transformation. Mechanistic studies point to an amine-directed reaction where CO₂ serves to protect the substrate and product from degradation.