engleski

PHOTOCHEMICAL AND THERMAL TRANSFORMATIONS OF w, w’ -ARYL/HETEROARYL/ALKYL SUBSTITUTED BUTADIENES

In order to prepare novel polycyclic structures by photochemical methodology, new o-substituted w, w’ -aryl/heteroaryl/alkyl-1, 3-butadienes 1a-c were synthesized and the photochemistry of the prolonged conjugated system was studied. Our previous results [1] on photochemistry of different heteroaryl substituted o-divinylbenzenes showed interesting intramolecular cycloaddition reactions and formation of bicyclo[3.2.1]octadiene structures. By insertion of additional double bond into the stilbene-like moiety the obtained octatetraene conjugated system (1) might allow formation of new polycyclic structures with a double bond functionality for further transformations. Moreover bicyclo[3.2.1]octane skeleton is found in numerous important biologically active natural products [2]. Upon irradiation of 1, 3-butadiene derivatives 1a-c the benzobicyclo[3.2.1]octa-2, 5-diene derivatives 2a-c are obtained in moderate to very good yield (40-90%). The photoreaction is stereoselective. In the case of 1a the formation of only one product is obtained whereas 1b and 1c give a mixture of endo- and exo-2b, c. Depending on the wavelength the formed benzobicyclo[3.2.1]octa-2, 5-diene derivative 2a undergoes di- -methane rearrangement to tricyclic structure 3 while 2b and 2c do not react. In the thermal reaction the new dihydronaphthalene-cyclobutane structures 4a-c are isolated as a result of octatetraene- followed by hexatriene-ring closure. Both, photochemical and thermal reaction mechanisms will be discussed. [1] D. Vidaković, I. Škorić, M. Horvat, Ž. Marinić, M. Šindler-Kulyk, Tetrahedron (2008) in press ; I. Škorić, N. Basarić, Ž. Marinić, A. Višnjevac, B. Kojić-Prodić, M. Šindler-Kulyk, Chem. Eur. J. 11 (2005) 543-551 and the references cited therein. [2] M.-H. Filippini, J. Rodriguez, Chem. Rev. 99 (1999) 27-76.

butadienes; photochemistry; polycycles; octatetraene; cycloaddition; thermal reaction

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