An efficient synthesis of unsymmetrical biphenols via the oxidative cross-coupling of two different phenols in the presence of K2S2O8 and Bu4N(+)·HSO3(-) (10 mol %) in CF3COOH at ambient conditions is described. 1:1 Cross-coupling of substituted phenols with naphthols and 1:2 cross-coupling of naphthols with phenol are also disclosed. By using Bu4N(+)·HSO3(-), the homocoupling of phenols or naphthols was controlled. In these reactions, the ortho C-H bond of two different phenols and the ortho and para C-H bond of phenols were coupled together.

A selectivity-driven catalyst design approach was adopted to address chemoselectivity issues in the oxidative coupling of phenols. This approach was utilized for developing a Co­(II)­[salen]-catalyzed aerobic oxidative cross-coupling of phenols in a recyclable 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) solvent. The waste-free conditions offer a sustainable entry to nonsymmetric biphenols via a mechanistic scheme that involves coupling of a liberated phenoxyl radical with a ligated 2-naphthoxyl radical.

A regioselective synthesis of unsymmetrical and symmetrical biphenols and binaphthols via oxidative coupling of phenols or naphthols in the presence of KSO in CFCOOH under ambient conditions is described. Interestingly, the 1 : 1 ratio of HO and CHCN solvent mixtures at 80 °C instead of CFCOOH provided substituted unsymmetrical quinones. A gram-scale synthesis of biphenols and binaphthols was demonstrated.

A novel type of chiral redox disulfonate iron complex for asymmetric catalysis is reported. The [Fe((R a )-BINSate)] + (BINSate = 1,1′binaphthalene-2,2′-disulfonate) complex effectively promotes the enantioselective oxidative cross-coupling between 2-naphthols (1) and 2-aminonaphthalene derivatives (2), affording optically enriched (R a )-2-amino-2′hydroxy-1,1′-binaphthyls (NOBINs) with exceptional yields and enantioselective ratios (up to 99% yield and 96:4 er). The [Fe((R a )-BINSate)] + catalyst was designed as a chiral version of FeCl 3 with multicoordination sites available for binding the two coupling partners 1 and 2 as well as the oxidant. Our structure−selectivity and activity study, which covered most of the important positions in the NOBIN scaffold, revealed the effect of different substitution patterns on the coupling efficiency and stereoselectivity.