A procedure was developed for the synthesis of a 18 crown 6 containing styryl dye of the pyridine series. Phototransformation products of the dye that formed upon irradiation with visible light in solution, films, and crystals were studied by 1 H and 13 C NMR spectroscopy and spectrophotometry. Irradiation of solutions of this dye in acetonitrile leads only to reversible E-Z photoisomerization of the C=C bond. Irradiation of a film of the dye induces stereospe cific [2+2] photocycloaddition to form exclusively the rctt isomer of tetrasubstituted cyclobutane. The latter was found to undergo base catalyzed isomerization giving rise to the rcct isomer. X ray diffraction study showed that photocycloaddition occurs in single crystals without their destruction. The structures of the E isomer of the dye and the resulting rctt isomer of the cyclobutane derivative were established. The characteristic features of the molecular packing of the dye favorable for topochemical photocycloaddition in the crystal and the structural changes that accompany the cyclobutane formation are discussed.

New styryl dyes of the pyridine and benzothiazole series were synthesized with the aim of investigating the solid state [2+2] autophotocycloaddition (PCA) reaction. The 1 H NMR spectroscopy showed that for most of the compounds under study, the visible light irradiation of thin polycrystalline films of the dyes affords cyclobutane derivatives. The rate of the photo reaction depends on the structure of the dye and is higher for compounds, which contain a short N substituent in the heterocyclic moiety and have strong absorption in the visible region. Dyes bearing electron releasing substituents in the benzene ring undergo the stereospecific PCA in the syn head to tail dimeric pair to give the only rctt isomer of cyclobutane derivatives. Electron withdrawing and bulky substituents in the benzene fragment of styryl dyes extend the range of the mutual orientations of the molecules in the dimeric pairs, resulting in the forma tion of two or even four isomeric cyclobutanes in the PCA reactions. The structures of some dyes were established by X ray diffraction. In the overwhelming majority of the structures, one of two packing modes, either syn head to tail or syn head to head, with extensive stacking interactions is observed. A rare example of the anti head to head stacking mode was found for the dicationic dye containing the bulky N + (Et)Me 2 substituent in the benzene ring. The syn head to tail and anti head to head stacking modes can facilitate the PCA reaction due to the close spatial proximity of the ethylenic bonds and their parallel orientation in the dimeric pairs of the dye molecules.

Both primary and secondary aliphatic nitro compounds 1 were found to react with two equivalents of bromotrimethylsilane in the presence of triethylamine followed by aqueous workup to give appropriate N,N-bis(trimethylsilyloxy)enamines 3 in good isolated yields. Products 3, starting from some secondary and/or sterically hindered compounds 1, are synthesized from the corresponding silyl nitronates 2.

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