An oxidative cleavage of C‒C double bond is developed from photochemical [2 + 2]-cycloaddition of diaryl N-tosyl enamides, aryl heteroaryl N-tosyl enamides, and N-tosyl cyclic enamides with singlet molecular oxygen followed by ring-opening reaction mediated by Cs₂CO₃ under air and sunlight without the use of photosesitizer, producing symmetrical and unsymmetrical diaryl, heterodiaryl, and cyclic ketones in good to excellent yields. Moreover, the oxidative cleavage of C‒C triple bonds from 1-alkynes is demonstrated for the synthesis of symmetrical and unsymmetrical ketones from Cu-catalyzed [3 + 2]-cycloaddition, Rh-catalyzed alkoxyarylation, photooxygenation, and ring-opening reaction in one-pot. Because synthesis of the symmetrical and unsymmetrical diaryl and/or heterodiaryl ketones bearing an electron-donating group is not easy, the present method is notable.