Modern photo- and electrochemical approaches to aryl radical generation

Aryl rings appear in a plethora of natural products and drugs. The vast majority of arylation processes still rely on the utilization of transition-metal complexes as catalysts. Another important strategy for introducing aryl rings into an organic skeleton operates through a radical pathway. The chemistry of aryl radicals has witnessed rapid development during the last few decades, especially as these species are crucial intermediates in many synthetically meaningful organic transformations, such as the Sandmeyer or Pschorr reactions. Predominately, they are prepared employing conventional redox reagents (oxidants or reductants) that are often used in large excess. In turn, recent developments in photocatalysis and synthetic electrochemistry allow for the assembly of Ar˙ species in a more sustainable and straightforward way; however, these advancements have not been timely and critically summarised to date. This review fills this obvious gap and sums up recent advances in processes involving Ar˙ by highlighting some challenges and identifying potential areas for improvement, which might inspire future research endeavors in this topic.