Direct Diacetylmethylation of Aromatic Compounds with Tris(2,4-pentanedionato)manganese(III)

Abstract The oxidation of naphthalenes with tris(2,4-pentanedionato)manganese(III) in acetic acid gave diacetylmethyl derivatives in good to moderate yields. Using excess amounts of the oxidant, the acetylmethyl-substituted naphthalenes were further oxidized and 3-acetoxy-3-naphthyl-2,4-pentanediones were obtained. The similar oxidation of anthracenes also produced (diacetylmethyl)anthracenes together with diacetylmethylene derivatives which were further oxidized. It was found that this direct diacetylmethylation was effective when the ionization potential of the aromatic compound was lower than 8.12 eV, and that the diacetylmethyl radical which was generated directly by the thermolysis of tris(2,4-pentanedionato)manganese(III) has an electrophilic nature based on the result of the oxidation of substituted naphthalenes. The reaction pathway for the oxidation of anthracene is also discussed.