REARRANGEMENTS IN THE CERIUM(IV) AND MANGANESE(III) OXIDATIONS OF SUBSTITUTED NAPHTHALENES AND THE NIH SHIFT MECHANISM

Ceric ammonium sulphate oxidation of 1- and 1,4- disubstituted naphtha lenes gives 2- and/or 2,3- disubstituted 1,4- naphthoquinones through migration of substituents (D, Br, Ph). Similar rearrangements are also observed in the manganese(III) oxidation and also in the anodic oxida tion of these substrates. The results are consistent with the proposal that these oxidations go through the formation of radical cation foll owed by reaction with H2O and further oxidation of the radical to the carbocationic intermediate on the way to the corresponding 1,4-naphtho quinone. Oxidation of 1,4-diphenylnaphthalene gives 2,3-diphenyl-1,4-n aphthoquinone or 4-hydroxy- 2,4- diphenyl - 1(4)R - naphthalenone. The results are in accordance with the conclusion that such rearrangement s do not require prior formation of arene oxide intermediates, origina lly proposed for the NM shift mechanism.