[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

Abstract

Upon UV irradiation 2-(dibenzylamino)ethyl 3-benzoylacrylate in a crystalline state undergoes efficient [2+2]photocycloaddition to give a head-to-tail dimer, bis[2-(dibenzylamino)ethyl] c-2,t-4-dibenzoylcyclobutane-r-1,t-3-dicarboxylate, quantitatively. The X-ray structure analysis shows CH/π interactions between aliphatic and aromatic C–H bonds and benzene rings make the orientation of the benzoylacrylate molecules in a crystalline state suitable for the [2+2]photocycloaddition. The aliphatic CH/π interaction is responsible for formation of the cis-configuration between the 2-(dibenzylamino)ethoxycarbonyl and benzoyl groups in the cyclobutanedicarboxylate. The cyclobutanedicarboxylate is hydrolyzed quantitatively to 2,4-dibenzoylcyclobutane-1,3-dicarboxylic acid, which is not directly produced from irradiation of crystals of 3-benzoylacrylic acid.