[2+2]photocycloaddition of 2-(dibenzylamino)ethyl 3-benzoylacrylate in a crystalline state: weak intermolecular interactions as important factors determining efficiency of the solid-state photoreaction

Upon UV irradiation 2-(dibenzylamino)ethyl 3-benzoylacrylate in a crystalli ne state undergoes efficient [2+2] photocycloaddition to give a head-to-tai l dimer, bis[2-(dibenzylamino)ethyl] c-2,t-4-dibenzoylcyclobutane-r-1,t-3-d icarboxylate, quantitatively. The X-ray structure analysis shows CH/pi inte ractions between aliphatic and aromatic C-H bonds and benzene rings make th e orientation of the benzoylacrylate molecules in a crystalline state suita ble for the [2+2] photocycloaddition. The aliphatic CH/pi interaction is re sponsible for formation of the cis-configuration between the 2-( dibenzylam ino) ethoxycarbonyl and benzoyl groups in the cyclobutanedicarboxylate. The cyclobutanedicarboxylate is hydrolyzed quantitatively to 2,4-dibenzoylcycl obutane-1,3-dicarboxylic acid, which is not directly produced from irradiat ion of crystals of 3-benzoylacrylic acid.