Photochemical reactivity of aromatic and heteroaromatic nitroderivatives in the presence of arylalkenes

Article abstract of DOI:10.1016/0040-4020(96)00878-2

The irradiation of styrene in the presence of nitroarenes in acetonitrile gives the corresponding nitrones in high yields. However, when 4-methyl-5-ethenylthiazole is used as arylalkene the starting material is converted to a pyrrole analogous of thianthrene. On the contrary, when 1,1-diphenylethylene is used, the main product observed is benzophenone. Nitrones are obtained only as minor products. An unusual coupling product, where a substitution reaction has occurred on the carbon bearing the nitro group, is also obtained. trans-Stilbene is unreactive under the same photochemical conditions, and it gives in low yields only benzaldehyde. Finally, indene gives, when aromatic nitro derivatives are used, only oxidation products, while, when heteroaromatic nitro derivatives are used, only substitution products on the nitro group are observed. The above described reactivity can be explained by using the results of AM1 semiempirical calculations on the frontier orbitals of the reagents. Both the nature of the LSOMO of the nitroarenes and the dipole moments of the reagents can account for the observed reactivity. The nitrone obtained in the photochemical reaction between styrene and nitrobenzene is used as starting material in a 1,3-dipolar cycloaddition reaction with styrene.