Choice of Manganese(III) Complexes for the Synthesis of 4,4'-Biphenyldiols and 4,4'-Diphenoquiones.

2,6-Disubstituted phenols are oxidized with tris(2,4-pentanedionato)manganese(III), [Mn(acac)3], in glacial acetic acid to give the corresponding 4,4′-biphenyldiols in high yields, whereas similar reactions using manganese(III) acetate, [Mn(OAc)3], insted of [Mn(acac)3] quantitatively yield the corresponding 4,4′-diphenoquinones. Cross-coupling reactions of 2,6-di-t-butylphenol and other substituted phenols afford the corresponding cross-coupled 4,4′-biphenyldiols and 4,4′-diphenoquinones together with oxidation products derived from the starting phenols themselves. The advantageous use of [Mn(acac)3] and [Mn(OAc)3] in the ubiqitous phenol coupling reaction is discussed.