γ-C(sp2)–H Arylation of Allylamines Using PdII and CO2 as a Transient Directing Group

Although C–H activation has become a powerful tool in the synthesis of complex molecules from simple precursors, transition metal-catalyzed reactions involving free alkenes often lead to insertion-type reactions. Herein we demonstrate that the addition of carbon dioxide in the form of dry ice allows the C(<i>sp</i>²)–H 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.