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Intramolecular photocyclization of new dithiophene-substituted o-divinylbenzenes

Thiophenes and their polycyclic derivatives represent a class of important and well-studied heterocycles [1]. The interest in this kind of compounds has spread from early dye chemistry to modern drug design and self-assembled superstructures. Unsaturated thiophene derivatives show a versatile photoreactivity and formations of various photoproducts with remarkable electrochemical, optical, physical and biological properties [1]. In aim to investigate the effect of sulphur moiety on photobehaviour of dithiophene-substituted o-divinylbenzenes, the novel 2, 2'-(1, 2-phenylenedivinylene)dithiophene (1), 2, 2'-(1, 2-phenylenedivinylene)-5, 5'-dimethyldithiophene (2), 2, 2'-(1, 2-phenylenedivinylene)-5, 5'-dibromodithiophene (3) were prepared, and their photochemistry is described for the first time. On irradiation, these sulphur diheteroaryles (1-3) undergo [1, 6] electrocyclization, followed by 1, 5-H shift and formation of dihydronaphtalenes (4-6), with traces of dimeric products. Described photobehaviour of dithiophene derivatives 1-3 is completely different from the previously investigated furan analogs [2], which undergo intramolecular cycloaddition reactions and formation of bicyclo[3.2.1.]octadiene structures.

photochemistry; thiophenes; intramolecular reactions; intermolecular reactions; photocycloadditions

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