engleski

Photochemical transformations of omega, omega'-aryl/heteroaryl substituted butadienes

Synthetic organic photochemistry, the chemistry of excited states of a molecule, differs from the ground state chemistry and provides a simple pathway to the complicated structures, heavily obtainable by a classic synthetic approach. Our group is interested in heterocyclic analogues of o-vinylstilbenes, i.e. b-heteroaryl (1) and b, b'-diheteroaryl (2) substituted o-divinylbenzenes [1] with oxygen, nitrogen or sulfur as heteroatom (Figure 1), with the objective to prepare new heteropolycyclic compounds, potentially biologically active substances. In order to prepare new polycyclic structures by the same methodology, new o-substituted omega, omega’ -aryl/heteroaryl -1, 3-butadienes 3a and 3b were synthesized and the photochemistry of this system with prolonged conjugation was studied. Upon irradiation of 3a and 3b interesting benzobicyclo[3.2.1]octadiene structures 4a and 4b with a double bond functionality for further transformations are obtained (Scheme 2) in very good yield (70-90%). Moreover bicyclo[3.2.1]octane skeleton is found in numerous important biologically active natural products. Extending the conjugated system by introduction of an additional double bond between the aromatic rings, allow formation of new complicated polycyclic structures in only one step. Upon irradiation of a mixture of isomers of 1, 3-butadiene derivative 3a, on 350 nm the endo-7-phenyl-2, 3-benzobicyclo[3.2.1]octa-2, 5-diene (4a) was isolated as the only product (Scheme 2). Photochemical reaction of 3a on 300 nm gave a mixture of the bicyclic structure 4a as a minor product and endo-7-phenyl-2, 3-benzotricyclo[3.2.1.04, 6]oct-2-ene (5a) as the major product.

photochemistry; butadienes; cycloaddition

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