Hydrogen-Bonding Organocatalysis Enabled Photocatalytic Intramolecular [2+2]-Cycloaddition Reaction

The combination of organocatalytic activation and photocatalysis for enabling the intramolecular [2+2]-cycloaddition of enone-ene substrates bearing one Lewis base binding site is reported. While in a variety of solvents a poor conversion or no reaction takes place in the absence of a hydrogen bonding catalyst, the corresponding ring-fused cyclobutane products could be built in moderate to good yields using a synergistic dual iridium-urea co-catalytic system. Control and mechanistic studies supported the postulated interaction between the organocatalyst and the substrate, which proved essential for an efficient energy transfer from the photosensitizer. image