Ozone-mediated nitration of bicumene and derivatives with nitrogen dioxide. Preferential mesolytic bond cleavage over nuclear nitration in evidence for the electron transfer nature of the kyodai-nitration of arenes

The ozone-mediated reaction of bicumene and some derivatives I with nitrogen dioxide in dichloromethane at low temperatures resulted in the facile cleavage of the central C-C bond to give the corresponding benzyl nitrate and its descendants 4-6. Mesolytic bond cleavage occurred almost exclusively over nuclear substitution at temperatures as low as -20 degrees C, especially at low concentration (2 x 10(-3) mol dm(-3)), This result may be rationalized in terms of initial electron transfer between the aromatic substrate and nitrogen trioxide generated in situ to form the aromatic radical cation, which then undergoes C-C bond scission at the benzylic position, In contrast, bibenzyl 2a is simply nitrated on the aromatic ring under similar conditions, giving the expected nitration products 7 and 8a-c along with a small amount of benzaldehyde 9. Results obtained from semi-empirical calculations and cyclic voltammetry are also in accord with the electron transfer nature of the reaction, The C-SI bond fission of benzyltrimethylsilane, C-C bond fragmentation of cyclic acetals of aromatic carbonyl compounds as wed as side-chain reactions of toluene and derivatives, have all previously been observed under certain conditions of the kyodai-nitration and can be understood on a similar basis as described above, The possible involvment of electron transfer processes in aromatic nitration with acetyl nitrate has also been suggested.