Lightening Diazo Compounds?

The development of new sustainable reactions and protocols is essential to fulfill the growing demands of every branch of organic chemistry for greener synthetic methodologies. In this context, the use of visible light as the only source of energy is highly appealing. Since diazo compounds are valuable reagents in organic synthesis, their transformations realized in a sustainable manner are of interest. High reactivity and easy availability make them suitable for solar-driven transformations. Indeed, photochemical reactions of diazo compounds have recently proven a valuable alternative to transition metal catalysis. In this perspective, we highlight applications of these reagents under visible irradiation, particularly focusing on recent advancements. These include photochemical generation of carbenes and radicals which involve many relevant reactions, 2+1-cycloadditions, X–H and C–H insertions, Wolff rearrangement, and more. Mechanistic aspects of these processes are briefly addressed to give readers a deeper understanding of rules underlying photoreactivity of diazo compounds. We conclude by emphasizing significant advancements and discussing challenges for future developments in the photochemistry of these valuable reagents.