ИСТИНА

The [2+2] photocycloaddition (PCA) reaction of unsaturated compounds is an important photoreaction used in synthetic organic chemistry. Cross-PCA, which takes place between different olefins, markedly expands the synthetic potential of the reaction. In the case where unsaturated electron donor and electron acceptor are used as the starting reactants, it is very difficult to predict the possibility and efficiency of cross-PCA. Herewith, the appearance of side photoprocesses, such as photoinduced charge transfer (PET) and energy transfer, which will result in low yield of the cyclobutane derivative, is possible. The introduction of a crown ether moiety into the structure of one olefin and an ammonioalkyl moiety into the structure of other olefin makes it possible to combine unsaturated compounds into pairs and carry out the cross-PCA reaction even in the presence of competing photoprocesses. The influence of donor substituents in the benzene ring of the styryl dye (E)-2a-d on the quantum yield of the cross-PCA reaction in pseudodimeric complexes of these dyes with (18-crown-6)styrylpyridine (E)-1a was studied. It was shown that the photoreaction proceeds stereospecifically with the formation of a single rctt isomer of the corresponding cyclobutane derivative 3a–d. It was shown that when the styrylpyridine moiety in the crown ether component is replaced by the stilbene moiety (E)-1b, PET from the donor (stilbene) to the acceptor (styryl dye) takes place in approximately half of the conformers of the (E)-1b•(E)-2b complex, which leads to a 5-fold drop in the quantum yield of cross-PCA. The results of the present study markedly expand the boundary conditions for conducting the cross-PCA reactions of diarylethylenes using the supramolecular assembly. They will also be useful for the development of methods for the synthesis of macrocyclic cyclobutanes as a new type of photoswitchable host molecules.