Investigation of photochemical behavior of furan derivatives containing an allomaltol fragment

Abstract

The photochemical behavior of terarylenes containing furan and allomaltol fragments was studied. It was demonstrated that starting 2-aminofurans containing 3-hydroxypyran-4-one moiety did not undergo any transformations under UV-irradiation. We supposed that all photoreactions are blocked due to the presence of amino group in the structure of the studied terarylenes. Wherein, the conversion of the amino group into pyrrole unit in the considered compounds allows one to unlock both 6π-electrocyclization of the 1,3,5-hexatriene system and ESIPT-promoted processes. At the same time, subsequent methylation of the hydroxyl group of allomaltol fragment leads to regiospecific photocyclization of terarylene core due to the suppression of ESIPT-induced reactions. Thus, UV-irradiation of methylated pyrrole-containing products results in 6π-electrocyclization of the 1,3,5-hexatriene system with the formation of polyaromatic compounds. Alternatively, ESIPT-promoted contraction of allomaltol moiety was observed in the cases when aforementioned 6π-electrocyclization is impossible. The structures of two synthesized products were established by X-ray diffraction.