Anion-Controlled Stereoselective Synthesis of Cyclobutane Derivatives by Solid-State [2 + 2] Cycloaddition Reaction of the Salts of <i>trans</i>-3-(4-Pyridyl) Acrylic Acid

Two stereoisomers of cyclobutane derivatives with pyridyl and carboxylic acid functionalities have been stereoselectively synthesized by a solid-state photochemical [2 + 2] cycloaddition reaction in quantitative yields. The head-to-head and head-to-tail parallel orientations of the monomers, required to obtain these two isomers, have been controlled by the anions present in the salts. The photoinert behavior of these salts in solution signifies the importance of the solid-state synthesis of these cyclobutane derivatives.