Chemoselective Photoreaction of Enamides: Divergent Reactivity towards [3+2]-Photocycloaddition vs Paternò-Büchi Reaction†.

Photoreaction of enamides tethered to a phenyl ketone leads to either [3+2]-photocycloaddition or Paternò-Büchi reaction. This divergence in chemical reactivity originating from the same excited state was dependent on the reaction temperature. At low temperatures the Paternò-Büchi reaction was preferred, whereas at higher temperatures there was preference toward formation of [3+2]-photoproduct.