prvi kongres hrvatskih znanstvenika iz domovine i inozemstva - HATZ

PRVI KONGRES HRVATSKIH ZNANSTVENIKA IZ DOMOVINE I INOZEMSTVAZagreb - Vukovar, 15. - 19. studenog 2004.P - 6PHOTOCHEMICAL TRANSFORMATION OF OXYGEN ANDNITROGEN HETEROSTILBENES TO POLYCYCLIC DERIVATIVESNikola Basarić 1 ; Kristina Butković 1 ; Irena Škorić 1 ; Željko Marinić 2 ; Marija Šindler-Kulyk 11 Faculty of Chemical Engineering and Technology, University of Zagreb, Croatia.2 NMR Center, The Ruñer Bošković Institute, Zagreb, CroatiaIn this presentation a review of our work, published (1-5) and unpublished, on thephotochemical behaviour and transformation of hexatriene system, partially inbeded inaromatic/heteroaromatic ring and substituted or disubstituted with furan, pyrrole andsydnone, to polycyclic derivatives will be illustrated.Heterostilbenes with the extended conjugation in ortho position undergo, besides alreadyknown electrocyclization reactions and formation of condensed heteroaromatics, diverseintramolecular cycloaddition reactions and formation of heteropolycyclic compoundsdepending on heteroatom.The furan heteroaromatic analogues of o-vinylstilbene 1a as well as the 5-furansubstituted derivatives undergo intramolecular cycloaddition and formation ofbenzobicyclo-[3.2.1]heptadiene structure with fused furan ring by initial [2+2]cycloaddition and formation of 1,4-biradical followed by allylic rearrangement and ringclosure. The pyrrole analogue of o-vinylstilbene 1b behaves quite different. It undergoesintermolecular addition of the pyrrole moiety at the position 5 to the double bond of theother molecule and formation of dimeric products. The vinyl-group does not participate inthe reaction. The reaction proceeds via electron transfer followed by hydrogen transferand radical combination. We succeeded to obtain the intramolecular reaction andformation of pyrrole fused benzobicyclo-[3.2.1]heptadiene structure by irradiation ofproperly nitrogen substituted pyrrole derivatives. Difuran derivative 1c, depending onconcentration and substitution, reacts intramolecularly giving benzobicyclo-[3.2.1]heptadiene structure or intermolecularly giving cyclophane derivative. Dipyrrolederivative 1d undergoes initial intramolecular reaction to the indane intermediate followedby nucleophilic attack of the starting compound or solvent. When the pyrrole ring is a partof hexatriene system, like in 1e, the reaction proceeds intramolecularly giving indole andisoindole derivatives. In the case of sydnone derivatives 1f and 1g, respectivelyphotochemical decarboxylation followed by intramolecular addition gives quinoline anddiazacyclopentalene derivative.Reaction mechanisms based on isolated products will be discussed.Presented on:XXth IUPAC Symposium on Photochemistry, Granada, Spain, 17-22.07.2004.Principal Investigator: Dr.sc. Marija ŠindlerProject No. 01250048