Topochemical Photopolymerization and Photo-Copolymerization of the Crystals of Unsymmetrically Substituted Diolefin Compounds Having Pyrimidine Ring

Abstract

Abstract Several new diolefin compounds, methyl and ethyl 4-[2-(4-pyrimidyl)ethenyl]cinnamates (1a and 1b), and methyl, ethyl, and propyl α-cyano-4-[2-(4-pyrimidyl)ethenyl]cinnamates (1c, 1d, and 1e) were synthesized, and their photoreactivity in the crystalline state was investigated. The crystals of 1c, 1d, and 1e gave amorphous oligomers having cyclobutane skeletons (average degree of polymerization was approximately 10) through the [2+2] photocycloaddition. The dimers (2c, 2d, and 2e) were formed in high yields by the exclusive photoexcitation of the monomers. The dimers were isolated by column chromatography. The cyclobutane structure of 2c and 2d was β-type homo adduct whereas that of 2e was β-type hetero adduct. As only one type of adduct was detected for each crystal, photodimerization was interpreted as being of a crystal lattice controlled process. The conversions of these reactions were not as high as that of the reaction in α-type of 2,5-distyrylpyrazine (DSP). The lower conversion was interpreted as being due to alternative reacting sites which inevitably result from the β-type molecular packing and to the drastic displacement of molecules which causes the distortion of crystal lattice. The mixed crystals (1f) of 1d and 1e (molar ratio 1.3/1), of which the X-ray diffraction pattern is similar to that of 1e, photopolymerized to give amorphous cooligomers (average degree of polymerization was approximately 5). The reaction went through an intermediate similar to dimer 2e.