PHOTOCHEMICAL REACTIVITY OF AROMATIC AND HETEROAROMATIC NITRODERIVATIVES IN THE PRESENCE OF ARYLALKENES

The irradiation of styrene in the presence of nitroarenes in acetonitr ile gives the corresponding nitrones in high yields. However, when 4-m ethyl-5-ethenylthiazole is used as arylalkene the starting material is converted to a pyrrole analogous of thianthrene. On the contrary, whe n 1,1-diphenylethylene is used the main product observed is benzopheno ne. Nitrones are obtained only as minor products. An unusual coupling product, where a substitution reaction has occurred on the carbon bear ing the nitro group, is also obtained. trans-Stilbene is unreactive un der 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 der ivatives are used only substitution products on the nitro group are ob served. The above described reactivity can be explained by using the r esults of AM1 semiempirical calculations on the frontier orbitals of t he reagents. Both the nature of the LSOMO of the nitroarenes and the d ipole moments of the reagents can account for the observed reactivity. The nitrone obtained in the photochemical reaction between styrene an d nitrobenzene is used as starting material in a 1,3-dipolar cycloaddi tion reaction with styrene. Copyright (C) 1996 Elsevier Science Ltd