A Chiral Iron Disulfonate Catalyst for the Enantioselective Synthesis of 2-Amino-2'-hydroxy-1,1'-binaphthyls (NOBINs).

A novel type of chiral redox disulfonate iron complex for asymmetric catalysis is reported. The [Fe((Ra)-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 (Ra)-2-amino-2'-hydroxy-1,1'-binaphthyls (NOBINs) with exceptional yields and enantioselective ratios (up to 99% yield and 96:4 er). The [Fe((Ra)-BINSate)]+ catalyst was designed as a chiral version of FeCl3 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.

Iron-Catalyzed Oxidative Cross-Coupling of Phenols and Tyrosine Derivatives with 3-Alkyloxindoles.

In this study, a novel iron-catalyzed oxidative cross-coupling reaction between phenols and 3-alkyloxindole derivatives is reported. The efficient method, which is based on the FeCl3 catalyst and the t-BuOOt-Bu oxidant in 1,2-dichloroethane at 70 °C, affords 3-alkyl-3-(hydroxyaryl)oxindole compounds with a high degree of selectivity. The generality of the conditions was proven by reacting various substituted phenols, naphthols, and tyrosine derivatives with 3-alkyloxindoles. To apply the chemistry for the conjugation of tyrosine-containing short peptides with oxindolylalanine (Oia) derivatives, the reaction conditions were modified [Fe(O2CCF3)3 catalyst, t-BuOOt-Bu, HFIP, 70 °C], and amino acids with acid-stable N-protecting groups were used.

Cobalt(II)[salen]-Catalyzed Selective Aerobic Oxidative Cross-Coupling between Electron-Rich Phenols and 2-Naphthols.

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.

Ruthenium-Catalyzed C-H Benzoxylation of tert-Benzamides with Aromatic Acids by Weak Coordination.

A highly regioselective C-H benzoxylation of tertiary benzamides with aromatic acids by weak O-amide coordination in the presence of [{RuCl2(p-cymene)}2], AgSbF6, and (NH4)2S2O8 in 1,2-dichloroethane at 100 °C for 24 h to afford ortho-benzoxylated tertiary benzamides is described. Selectively, ortho-benzoxylated cyclic benzamides were converted into ortho-benzoxylated benzaldehydes by using Cp2ZrHCl at room temperature. Subsequently, substituted salicylic acids were prepared by deprotection of the ester and amide groups of ortho-benzoxylated cyclic benzamides.

Solvent-controlled selective synthesis of biphenols and quinones via oxidative coupling of phenols.

A regioselective synthesis of unsymmetrical and symmetrical biphenols and binaphthols via oxidative coupling of phenols or naphthols in the presence of K2S2O8 in CF3COOH under ambient conditions is described. Interestingly, the 1 : 1 ratio of H2O and CH3CN solvent mixtures at 80 °C instead of CF3COOH provided substituted unsymmetrical quinones. A gram-scale synthesis of biphenols and binaphthols was demonstrated.

Oxidative Cross-Coupling of Two Different Phenols: An Efficient Route to Unsymmetrical Biphenols.

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 regioselective synthesis of benzopinacolones through aerobic dehydrogenative α-arylation of the tertiary sp3 C-H bond of 1,1-diphenylketones with aromatic and heteroaromatic compounds.

A regioselective synthesis of symmetrical and unsymmetrical benzopinacolones through aerobic dehydrogenative α-arylation at the tertiary sp(3) C-H bond of substituted 1,1-diphenylketones with aromatic and heteroaromatic compounds, in the presence of K2S2O8 in CF3COOH at room temperature, is described. The reaction is proposed to go via a carbocation intermediate, which could be generated directly from cleavage of the sp(3) C-H bond of 1,1-diphenylketone. Subsequent α-arylation was achieved at the methene sp(3) carbon atom of the substituted ketone. A variety of substituted aromatic and heteroaromatic compounds were compatible with this reaction. In addition, benzopinacolones were converted into sterically hindered, tetrasubstituted alkenes and polycyclic aromatic compounds.

Aerobic dehydrogenative α-diarylation of benzyl ketones with aromatics through carbon-carbon bond cleavage.

Substituted benzyl ketones reacted with aromatics in the presence of K2S2O8 in CF3COOH at room temperature, yielding α-diaryl benzyl ketones through a carbon-carbon bond cleavage. In the reaction, two new carbon-carbon bonds were formed and one carbon-carbon bond was cleaved. It is very interesting that two different nucleophiles such as benzyl ketones and aromatics were coupled together without metal, which is unusual in organic synthesis.