Photochemistry of Phthalimides with Olefins. Solvent-Incorporated Addition vs. Cycloaddition to Imide C(=O)-N Bond Accompanying Ring Enlargement

Article abstract of DOI:10.1021/jo00209a015

The photoreactions of phthalimides 1a-c and a variety of olefins (2a-g) have been investigated.Irradiation of methanol solutions of 1a in the presence of electron-rich olefins 2a-f leads to formation of methanol-incorporated adducts 3a + 4a, 9a,b, 19, 29a,b, 30a,b, and 31.Irradiation of acetonitrile solutions of 1a in the presence of relatively electron-poor aliphatic olefins 2f,g gives ring enlarged cycloddition products 23, 32, and 34, probably by a mechanism which involves collapse of an exciplex.Photolyses of 1a and 2a in less polar alcohols afford the two typesof products, simultaneously.With decrease of the solvent polarity, the yields of the solvent-incorporated adducts decrease and that of the ring-enlarged cycloaddition products increase.Irradiation of 1a and 2c leads to formation of the other types of products: in methanol 20 is obtained together with 19, and in acetonitrile 22 and 24 are formed together with 23.The formation of 24 is rationalized by a mechanism in which degradation of an oxetane (27) is involved.The products 20 and 22 appear to be derived through electron transfer from 2c to the excited state of 1a.Phenanthrene (electron-transfer) sensitization of the reaction 1a + 2c gives 20 and 23 in methanol and 22 in acetonitrile, selectively.These results and ΔG values associated with the electron transfer support an electron-transfer mechanism for the solvent-incorporated adduct formation.