Reconnaissance of reactivity of an Ag(ii)SO4 one-electron oxidizer towards naphthalene derivatives

Abstract

We test divalent silver sulphate, Ag(II)SO₄ as a novel reagent for oxidative coupling of aromatic hydrocarbons under ambient temperature conditions. The applicability of the C(sp²)–C(sp²) coupling protocol is illustrated for naphthalene and its 1-substituted derivatives containing either electron donating (e.g. Me, MeO, or Ph) or electron-withdrawing groups (X = F⋯I), leading to 4,4′-disubstituted-1,1′-binaphthyls. Coupling of 2-bromo-naphthalene yields a mixture of 2,2′-, 2,7′-, and 7,7′-dibromo-1,1′-binaphthyls together with their trimeric and tetrameric analogues. The coupling of strongly electron-withdrawing 1-CF₃-naphthalene provides the 5,5′-disubstituted-1,1′-binaphthyl derivative. The new method does not require the presence of halogen substituents, in contrast to most of the known C–C coupling methods, and it preserves them, if present. Ag(II)SO₄ may be easily electrochemically regenerated from the Ag(I)HSO₄ byproduct. However, the C–C coupling method currently suffers from low yields, up to 17%, and it requires further optimization.