Abstract: The generation of acyl radicals from phenyl selenoesters and the scope of their participation in macrocyclization free-radical alkene addition reactions are detailed. The studies illustrate that large ring w-acryloyl radical cyclizations proceed at rates competitive with those of 5-exo-trig cyclization of 5-hexenoyl radicals and that exceed those of 6-exo-or 7-endo-trig cyclization of 6-heptenoyl radicals, thus providing an effective ...