Catalytic dehydrogenative cross-coupling: forming carbon-carbon bonds by oxidizing two carbon-hydrogen bonds

The selective oxidation of C-H bonds and the use of O(2) as a stoichiometric oxidant represent two prominent challenges in organic chemistry. Copper(II) is a versatile oxidant, capable of promoting a wide range of oxidative coupling reactions initiated by single-electron transfer (SET) from electron-rich organic molecules. Many of these reactions can be rendered catalytic in Cu by employing molecular oxygen as a stoichiometric oxidant to regenerate the active copper(II) catalyst. Meanwhile, numerous other recently reported Cu-catalyzed C-H oxidation reactions feature substrates that are electron-deficient or appear unlikely to undergo single-electron transfer to copper(II). In some of these cases, evidence has been obtained for the involvement of organocopper(III) intermediates in the reaction mechanism. Organometallic C-H oxidation reactions of this type represent important new opportunities for the field of Cu-catalyzed aerobic oxidations.

Copper-Catalyzed Aerobic Oxidative C ? H Functionalizations: Trends and Mechanistic Insights

Transition metal-mediated C–H bond activation and functionalization represent one of the most straightforward and powerful tools in modern organic synthetic chemistry. Bi(hetero)aryls are privileged π-conjugated structural cores in biologically active molecules, organic functional materials, ligands, and organic synthetic intermediates. The oxidative C–H/C–H coupling reactions between two (hetero)arenes through 2-fold C–H activation offer a valuable opportunity for rapid assembly of diverse bi(hetero)aryls and further exploitation of their applications in pharmaceutical and material sciences. This review provides a comprehensive overview of the fundamentals and applications of transition metal-mediated/catalyzed oxidative C–H/C–H coupling reactions between two (hetero)arenes. The substrate scope, limitation, reaction mechanism, regioselectivity, and chemoselectivity, as well as related control strategies of these reactions are discussed. Additionally, the applications of these established methods in the s...

Oxidative C-H/C-H Coupling Reactions between Two (Hetero)arenes.

Does the dehydrogenative coupling of aromatic compounds mediated by AlCl3 at high temperatures and also by FeCl3, MoCl5, PIFA, or K3[Fe(CN)6] at room temperature proceed by the same mechanism in all cases? With the growing importance of the synthesis of aromatic compounds by double C-H activation to give various biaryl structures, this question becomes pressing. Since some of these reactions proceed only in the presence of non-oxidizing Lewis acids and some only in the presence of certain oxidants, the authors venture the hypothesis that, depending on the electronic structure of the substrates and the nature of the "catalyst", two different mechanisms can operate. One involves the intermediacy of a radical cation and the other the formation of a sigma complex between the acid and the substrate. The goal of this Review is to encourage further mechanistic studies hopefully leading to an in-depth understanding of this phenomenon.

Comparison of Oxidative Aromatic Coupling and the Scholl Reaction

Biaryls constitute an important subunit found in medicinal agents, functional materials, and natural products. While the Suzuki reaction and related processes currently represent the method of choice for the construction of arene–arene bonds, the direct-coupling of two unfunctionalized arenes mediated by the addition of an oxidant represents a powerful alternative strategy for biaryl synthesis. This tutorial review describes recent progress in this rapidly developing field, focusing on intermolecular examples of selective arene oxidation strategies and metal-catalyzed oxidative cross-coupling via C–H activation.

Intermolecular oxidative cross-coupling of arenes

Highly selective oxidative cross-coupling of substituted 2-naphthols: A convenient approach to unsymmetrical 1,1′-binaphthalene-2,2′-diols

An optimized synthesis of dimethyl 2,2′-dihydroxy-1,1′-binaphthalene-3,3′-dicarboxylate and of methyl 2,2-dihydroxy-1,1′-binaphthalene-3-carboxylate

An Optimized Synthesis of Dimethyl 2,2′‐Dihydroxy‐1,1′‐binaphthalene‐3, 3′‐dicarboxylate and of Methyl 2,2′‐Dihydroxy‐1,1′‐binaphthalene‐3‐ carboxylate.

Martin Hovorka

Papers

Highly selective oxidative cross-coupling of substituted 2-naphthols: A convenient approach to unsymmetrical 1,1′-binaphthalene-2,2′-diols

An optimized synthesis of dimethyl 2,2′-dihydroxy-1,1′-binaphthalene-3,3′-dicarboxylate and of methyl 2,2-dihydroxy-1,1′-binaphthalene-3-carboxylate

An Optimized Synthesis of Dimethyl 2,2′‐Dihydroxy‐1,1′‐binaphthalene‐3, 3′‐dicarboxylate and of Methyl 2,2′‐Dihydroxy‐1,1′‐binaphthalene‐3‐ carboxylate.

The Oxidative Cross-Coupling of Substituted 2-Naphthols. Part 1. The Scope and Limitations.