Interconversion and rearrangement of radical cations .2. Photoinduced electron transfer and electrochemical oxidation of 1,4-bis(methylene)cyclohexane

The photoinduced electron transfer and electrochemical oxidation of 1,4-bis(methylene)cyclohexane (2) in acetonitrile have been studied in the presence and absence of a nucleophile (methanol). The photoinduced electron transfer reactions of 2 in acetonitrile-methanol solution with 1,4-dicyanobenzene (8) as the electron acceptor gives two products: 4-(methoxymethyl)-1-methylenecyclohexane (16) and 4-(4-cyanophenyl)-4-(methoxymethyl)-1-methylenecyclohexane (17). These products arise from nucleophilic attack on the radical cation followed by either reduction and protonation or combination with the radical anion of the electron acceptor, 1,4-dicyanobenzene (8(.-)). These results are in accord with the proposed mechanism of the photochemical nucleophile-olefin combination, aromatic substitution (photo-NOCAS) reaction, In the absence of a nucleophile, the photoinduced electron transfer reaction of 2 gives rise to several interesting and unexpected products 18-25 which result from complex reaction mechanisms involving radical, ionic and radical ion intermediates. The electrooxidation of 2 in acetonitrile in the presence of methanol leads to products 27-35, Under these conditions the radical cation 2(.+) reacts with the nucleophile followed by a second oxidation and subsequent reactions leading to products (electrochemical-chemical-electrochemical, ECE), One of the products (28) is the result of protonation of 2 followed by nucleophilic attack. The electrochemical oxidation of 2 in acetonitrile (no methanol) yields 2(.+) which is deprotonated and then further oxidized to give 39-43. These products arise from ionic Intermediates (ECE); oxidation of 2 all the way to aromatic compounds was observed in 39-41. In none of these experiments was there any evidence for the formation of cyclized products, nor was there any indication of carbon-carbon bond cleavage in 2(.+), The products are consistent with the initial formation of the intermediate radical cation, The products as well as the possible mechanisms of formation of these species are discussed.