A novel strategy to trap iminyl radicals with copper ions has been developed at room temperature, the resulted high-valent Cu(III) imine intermediate resets quickly to form nitrene and then to furnish a 2H-azirine. This protocol with dual copper/photoredox catalyst enables the selective imination of unactivated C-H bonds under mild conditions with a broader scope. Moreover, this method also uncovers a novel ring-expansion rearrangement from cyclobutyl oxime derivatives to give the α-acylamino cyclopentanones.