2,2′-Biaryldicarboxylate Synthesis via Electrocatalytic Dehydrogenative C–H/C–H Coupling of Benzoic Acids

Electrochemical meta-C-H sulfonylation of pyridines with nucleophilic sulfinates

Considering the indispensable significance and utilities of meta-substituted pyridines in medicinal, chemical as well as materials science, a direct meta-selective C-H functionalization of pyridines is of paramount importance, but such reactions remain limited and highly challenging. In general, established methods for meta C-H functionalization of pyridines rely on the utilization of tailored electrophilic reagents to realize the intrinsic polarity match. Herein, we report a complementary electrochemical methodology; diverse nucleophilic sulfinates allow meta-sulfonylation of pyridines through a redox-neutral dearomatization-rearomatization strategy by a tandem dearomative cycloaddition/hydrogen-evolution electrooxidative C-H sulfonation of the resulting oxazino-pyridines/acid-promoted rearomatization sequence. Besides, several salient features, including exclusive regiocontrol, remarkable substrate/functional group compatibility, scale-up potential, and facile late-stage modification, have been demonstrated, which further contributes to the practicality and adaptability of this approach.

Rhodaelectro-Catalyzed Decarboxylative Cross-Dehydrogenative Coupling of Indole-3-carboxylic Acids and Olefins via Weakly Coordinating Carboxyl Groups

A rhodaelectro-catalyzed C2-H selectively decarboxylative alkenylation of 3-carboxy-1H-indoles employing electricity as the traceless terminal oxidant has been accomplished. The weakly coordinating carboxyl group serves as the traceless directing groups. External oxidant-free in an undivided cell with constant current in aqueous solution ensures the decarboxylative C-H alkenylation to be viable and sustainable.

Ni-Catalyzed Protecting Group Free Diphenic Acid Analog Synthesis

Severe side effects and drug resistance are major drawbacks of Pt-based chemotherapy in clinical practice, leading to the search for new Pt-based drugs through the tuning of coordination ligands. Therefore, seeking appropriate ligands has attracted significant interest in this area. In this study, we report a Ni-catalyzed coupling strategy for the divergent synthesis of diphenic acid derivatives and the application of these newly prepared acids in Pt(II) agent synthesis.

Electrochemical C-H Sulfonylation of Hydrazones

We have developed an electrochemical method for the direct C-H sulfonylation of aldehyde hydrazones using sodium sufinates as the sulfonylating agent under supporting electrolyte-free conditions. This straightforward sulfonylation strategy afforded a library of (E)-sufonylated hydrazones with high tolerance of various functional groups. The radical pathway of this reaction has been revealed by the mechanistic studies.

Recent Advances in the Electrochemical Functionalization of Isocyanides

Isocyanides are well-known as efficient CO surrogates and C1 synthons in modern organic synthesis. Although tremendous efforts have been devoted to fully exploiting the reactivity of isocyanides, these transformations are primarily limited by their utilization of stoichiometric toxic chemical oxidants. With the recent resurgence of organic electrochemistry, which has considerably laid dormant over the past several decades, electrolysis has been identified as a green and powerful tool to enrich structural diversity by solely utilizing electric current as clean and inherently safe redox equivalents of stoichiometric chemical oxidants. In this regard, the unique reactivity of isocyanides has been studied in numerous electrochemical transformations. This review comprehensively highlights the most relevant progress in electrochemical strategies towards the functionalization of isocyanides up until June of 2022, with a focus on reaction outcomes and mechanisms.

Electrochemical Rhodium-Catalyzed C-H Cyclodimerization of Alkynes to Access Diverse Functionalized Naphthalenes: Involvement of RhIV/V and RhI Dual Catalysis

The first electrochemical rhodium-catalyzed C-H cyclodimerization of alkynes for the direct construction of functionalized naphthalenes was reported. The practicality and synthetic value of this strategy were demonstrated by the readily accessible scale-up synthesis and transformation of the products. Detailed mechanistic studies evidenced that electricity played an important role during the electrochemical disproportionation (ECD) process to generate and maintain the catalytically active Rh^IV/V and Rh^I species, which conducted the direct C-H activation.

Chemodivergent Synthesis of Indeno[1,2-b]indoles and Isoindolo[2,1-a]indoles via Mn(III)-Mediated or Electrochemical Intramolecular Radical Cross-Dehydrogenative Coupling

Chemodivergent synthesis of indeno[1,2-b]indoles and isoindolo[2,1-a]indoles from the same starting materials involving radical cross-dehydrogenative couplings have been developed. Mn(OAc)₃·2H₂O selectively promoted an intramolecular radical C-H/C-H dehydrogenative coupling reaction to provide indeno[1,2-b]indoles, while an intramolecular radical C-H/N-H dehydrogenative coupling reaction could proceed via electrochemistry to deliver isoindolo[2,1-a]indoles. Plausible mechanisms of the chemodivergent reactions were proposed.

Distal Ruthenaelectro-Catalyzed meta-C-H Bromination with Aqueous HBr

While electrochemical ortho‐selective C−H activations are well established, distal C−H activations continue to be underdeveloped. In contrast, we herein describe the electrochemical meta‐C−H functionalization. The remote C−H bromination was accomplished in an undivided cell by RuCl₃⋅3 H₂O with aqueous HBr. The electrohalogenation proceeded under exogenous ligand‐ and electrolyte‐free conditions. Notably, pyrazolylarenes were meta‐selectively brominated at the benzenoid moiety, rather than on the electron‐rich pyrazole ring for the first time. Mechanistic studies were suggestive of an initial ruthenacycle formation, and a subsequent ligand‐to‐ligand hydrogen transfer (LLHT) process to liberate the brominated product.

Ester-directed orthogonal dual C-H activation and ortho aryl C-H alkenylation via distal weak coordination

An unprecedented orthogonal cross-coupling between aromatic C(sp²) and aliphatic olefinic C(sp²) carbons of two same molecules via dual C-H bond activation in an intermolecular fashion has been developed using a distal ester-directing group. This new coupling reaction led to the synthesis of the highly functionalized 1,3-diaryl molecular architecture in very good yields and with high chemo- and regioselectivities. In addition, using ester as the distal directing group, ortho C-H olefination of α-methyl aryl acrylates and cinnamic esters with various alkenes has been achieved in very good yields and with a wide range of substrate scope.

Recent advances in rhodium-catalysed cross-dehydrogenative-coupling between two C(sp2)-H bonds

Rhodium-catalysed cross-dehydrogenative coupling (CDC) has received considerable attention in recent years. This modern technology has been considered as an attractive synthetic tool for selective C−C bond formation due to (1)...

Efficient one-step synthesis of 3-(indol-2-yl)quinoxalin-2(1H)-ones via electrochemical oxidative cross-dehydrogenative coupling

A novel and efficient synthetic strategy for 3-(indol-2-yl)quinoxalin-2(1H)-ones was developed via electrochemical oxidative cross-dehydrogenative coupling of indoles and quinoxalin-2(1H)-ones.

Recent advances in organic electrosynthesis employing transition metal complexes as electrocatalysts

Organic electrosynthesis has been widely used as an environmentally conscious alternative to conventional methods for redox reactions because it utilizes electric current as a traceless redox agent instead of chemical redox agents. Indirect electrolysis employing a redox catalyst has received tremendous attention, since it provides various advantages compared to direct electrolysis. With indirect electrolysis, overpotential of electron transfer can be avoided, which is inherently milder, thus wide functional group tolerance can be achieved. Additionally, chemoselectivity, regioselectivity, and stereoselectivity can be tuned by the redox catalysts used in indirect electrolysis. Furthermore, electrode passivation can be avoided by preventing the formation of polymer films on the electrode surface. Common redox catalysts include N-oxyl radicals, hypervalent iodine species, halides, amines, benzoquinones (such as DDQ and tetrachlorobenzoquinone), and transition metals. In recent years, great progress has been made in the field of indirect organic electrosynthesis using transition metals as redox catalysts for reaction classes including C-H functionalization, radical cyclization, and cross-coupling of aryl halides-each owing to the diverse reactivity and accessible oxidation states of transition metals. Although various reviews of organic electrosynthesis are available, there is a lack of articles that focus on recent research progress in the area of indirect electrolysis using transition metals, which is the impetus for this review.

Biaryl Synthesis via Electrooxidative Transition-Metal-Catalyzed C–H Activation

The use of electricity as an inexpensive and waste-free oxidant opens up new opportunities for the development of sustainable C–H functionalization reactions. Herein we summarize recent advances in the synthesis of biaryls through electrooxidative processes involving transition-metal-catalyzed ortho-directed C–H activation. A particular focus is set on electrooxidative C–H/C–M couplings and dehydrogenative couplings.

1 Introduction

2 Electrooxidative C–H/C–M Couplings

3 Electrooxidative C–H/C–H Couplings

4 Conclusion and Outlook