On the mechanism of the photochemical reaction between 1,4-dicyanobenzene and 2,3-dimethylbutene in the prsence of nucleophiles

The irradiation of 1,4-dicyanobenzene (DCB) in the presence of 2,3-dimethyl-2-butene (DMB) leads to allylation of the aromatic. In the presence of nucleophiles (MeOH, H2O, CF3CH2OH) this reaction is substituted by the nucleophile olefin combination - aromatic substitution (NOCAS) process. The quantum yield increases from 0.006 in the absence to a limiting value of ca 0.02 in the presence of the nucleophiles. The reaction involves competing deprotonation and nucleophile addition to the olefin radical cation, followed by coupling of the thus formed radical with DCB−. Minor processes are hydrogen abstraction from the solvent by the allyl radical, revealed by isolation of the phenylpentanonitrile 3 and coupling of the radical ions before separation, revealed by a small amount of the cyclohexadiene 6.