2,4,6-Triisopropyl-4’-carboxybenzophenone was converted to the cyclobutenol derivative with the optical yield of e.e.=30% by the irradiation of its salt complex with L-prolinol. This solid state reaction proceeds without the decomposition of the crystal and the structures of the salt crystals before and after irradiation were determined using the X-ray method. In the asymmetric units of both structures, there are two independent molecules, which are related by pseudo glide plane. This pseudo symmetric arrangement of the two molecules is due to the weak chirality of L-prolinol and is responsible for the low optical yield of the reaction.