Photochemical Reactivity of 1-Substituted-1-aza-1,4-dienes Promoted by Electron-Acceptor Sensitizers. Di-π-methane Rearrangements and Alternative Reactions via Radical-Cation Intermediates

Irradiation of a series of β,γ-unsaturated imines, oxime acetates, and oxime methyl ethers, using 9,10-dicyanoanthrathene (DCA) or dicyanodurene (DCD) as electron acceptor sensitizers, affords the corresponding cyclopropanes resulting from 1-aza-di-π-methane rearrangements via radical cations. In some cases, alternative reactions of these intermediates occur to yield nitriles, dihydroquinolines, dihydronaphthalene derivatives, and cycloaddition products. Some of these products result from reactions via alkene radical-cation intermediates while others arise by pathways involving imine radical-cation intermediates. The yields of products formed in these processes were significantly higher when DCD was used as electron-acceptor sensitizer instead of DCA.