Radical-cations from arenes reactions with nucleophiles

Pandey and co-workers have generated arene radical cations by PET from electron-rich aromatic rings [119]. The photoreaction is apparently initiated by single-electron transfer from the excited state of the arene to ground state 1,4-dicyanonaphthalene (DCN) in an aerated aqueous solution of acetonitrile. Intramolecular reaction with nucleophiles leads to anellated products regio-specifically. The author explains the regiospecifidty of the cyclization step from... 

Photoamination of a variety of aromatic compounds with ammonia and alkyl-amines under photosensitized electron transfer mediated reaction conditions has been extensively investigated by Yasuda and coworkers (Scheme 70) [320-324]. The photoamination reactions of stilbene derivatives with ammonia have been utilized for the synthesis of a variety of isoquinoline derivatives [324]. The photoamination is initiated by photochemical electron transfer from the arenes to the electron acceptor followed by nucleophilic attack of ammonia or primary amines on the aromatic radical cations (Scheme 70). 

In keeping with the seminal work of Kita, we proposed that the I(III)-mediated amination involved a radical cation intermediate that was generated by single electron transfer from the arene to the I(III) oxidant. The consequent radical cation should be highly reactive, and the attack of a phthalimide nucleophile would lead to a mixture of regiomeric products, like the 5 6 3 mixture that was observed for our toluene reaction (Scheme 10). This hypothesis contrasts with the mechanisms proposed by Chang and Antonchick, as electrophilic aromatic substitution, even with a reactive R2N species, should favor the para product. 

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