Transition metal-catalysed allylic functionalization reactions involving radicals
Transition metal-catalysed allylic functionalization reactions have been established as a central synthetic transformation to enable the construction of carbon–carbon and carbon–heteroatom bonds. Although they have been widely investigated by numerous research groups all over the world, frequently applied in drug discovery and natural product synthesis, most research endeavours focus on ionic mechanisms. Transition metal-catalysed allylic functionalization reactions involving radicals are comparatively underexplored, but provide a powerful alternative strategy to current approaches, considerably extending the amenable coupling partners. This tutorial review highlights the recent advances in this rapidly expanding area, which experienced an unprecedented momentum thanks to the rapid development of radical chemistry. The rationalization of the main scenarios in the generation of allylic intermediates, radical species as formal nucleophiles, and activated transition metals as well as the utilization of allylic radical intermediates in β-functionalization of carbonyls will highlight the common mechanistic threads. In addition the extension of amenable substrates and the new product motifs that can be generated will be summarized.