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

摘要

Upon UV irradiation 2-(dibenzylamino)ethyl 3-benzoylacrylate in a crystalline stat eundergoes 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 anaysis shows CH/#pi# 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/#pi# 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.