Reductive radical chain initiation through the thermal generation of carbon dioxide radical anion

Radical chain initiation strategies are fundamental to the synthesis of small molecule drugs and macromolecular materials. Modern methods for initiation through one-electron reduction are largely dominated by photo- and electrochemistry but the large-scale industrial application of these methods is often hampered by scalability challenges. Here we report a general, thermally driven and scalable method for the reductive initiation of radical chains that involves reacting an inexpensive azo initiator with a formate salt to form a carbon dioxide radical anion. Substoichiometric quantities of this initiator system were used to form C(<i>sp</i> ²)-C(<i>sp</i> ³), C(<i>sp</i> ²)-S, C(<i>sp</i> ²)-H, C(<i>sp</i> ²)-B and C(<i>sp</i> ²)-P bonds from complex (hetero)aryl halides, with high chemoselectivity and under transition-metal-free conditions. The developed initiator system was also used to probe the mechanism of other radical reactions.