The visible light-mediated copper(II)-catalyzed one-step synthesis of isoxazolines and isoxazoles from readily available ethyl nitroacetate or phenyl nitromethane is reported. The developed protocol eliminates the need for substrate preactivation or additives, and offers an extensive scope of activated and unactivated alkenes and alkynes as coupling partners. Key intermediates for this formal [3 + 2]-cycloaddition are α-nitro radicals generated via photoinduced single-electron oxidation of nitronates, contrasting the generation of such radicals via Cu(I)-photocatalysis by a reductive pathway, which shows a different reaction pattern in the coupling with alkenes.