Synthesis of Diketones, Ketoesters, and Tetraketones by Electrochemical Oxidative Decarboxylation of Malonic Acid Derivatives: Application to the Synthesis of cis-Jasmone

Electrochemical Synthesis of Unnatural Amino Acids via Anodic Decarboxylation of N-Acetylamino Malonic Acid Derivatives

Broad application of α,α-disubstituted cyclic amino acid derivatives in medicinal chemistry urges for analogue design with improved pharmacokinetic properties. Herein, we disclose an electrochemical approach toward unnatural THF- and THP-containing amino acid derivatives that relies on anodic decarboxylation-intramolecular etherification of inexpensive and readily available N-acetylamino malonic acid monoesters under Hofer-Moest reaction conditions. The decarboxylative cyclization proceeds under constant current conditions in an undivided cell in an aqueous medium without any added base. A successful bioisosteric replacement of the 1-aminocyclohexane-1-carboxylic acid subunit by the THP-containing amino acid scaffold in cathepsin K inhibitor balicatib helped to reduce lipophilicity while retaining low nanomolar enzyme inhibitory potency and comparable microsomal stability.

Synthesis of Thioureas, Thioamides, and Aza-Heterocycles via Dimethyl-Sulfoxide-Promoted Oxidative Condensation of Sulfur, Malonic Acids, and Amines

Malonic acid and derivatives have been well-known to undergo monodecarboxylation under relatively mild conditions and have been exclusively used as a C2 synthon. We report herein their new application as a C1 synthon via double decarboxylation promoted by sulfur and dimethyl sulfoxide. In the presence of amines as nucleophiles, a wide range of thioureas and thioamides as well as N-heterocycles were obtained in good to excellent yields under mild heating conditions.

Manganese(III) porphyrin-catalyzed regioselective dual functionalization of C(sp3)-H bonds: the transformation of arylalkanes to 1,4-diketones

The first, direct way from arylalkanes to 1,4-dicarbonyl compounds has been shown. It makes obtaining these useful products more accessible and cheaper. Our method is based on a one-pot reaction with excellent regioselectivity, mild conditions, and water as the main solvent. A plausible reaction mechanism has also been proposed.

Beyond Kolbe and Hofer-Moest: Electrochemical Synthesis of Carboxylic Anhydrides from Carboxylic Acids

Herein we report a conceptually new non-decarboxylative electrolysis of carboxylic acids to obtain their corresponding anhydrides as highly valuable reagents in organic synthesis. All carbon atoms of the starting material are preserved in the product in an overall redox-neutral reaction. In a broad substrate scope of carboxylic acids the anhydrides are generated with high selectivity, which demonstrates the versatility of the developed method. Beneficially, no dehydrating reagents are required in comparison to conventional methods and the synthesis is based on uncritical starting materials using graphite and stainless steel as very inexpensive and eco-friendly electrode materials.

Synthetic Molecular Photoelectrochemistry: New Frontiers in Synthetic Applications, Mechanistic Insights and Scalability

Synthetic photoelectrochemistry (PEC) is receiving increasing attention as a new frontier for the generation and handling of reactive intermediates. PEC permits selective single‐electron transfer (SET) reactions in a much greener way and broadens the redox window of possible transformations. Herein, the most recent contributions are reviewed, demonstrating exciting new opportunities, namely, the combination of PEC with other reactivity paradigms (hydrogen‐atom transfer, radical polar crossover, energy transfer sensitization), scalability up to multigram scale, novel selectivities in SET super‐oxidations/reductions and the importance of precomplexation to temporally enable excited radical ion catalysis.

Advances in Electrochemical Decarboxylative Transformation Reactions

Owing to their non-toxic, stable, inexpensive properties, carboxylic acids are considered as environmentally benign alternatives as coupling partners in various organic transformations. Electrochemical mediated decarboxylation of carboxylic acid has emerged as a new and efficient methodology for the construction of carbon-carbon or carbon-heteroatom bonds. Compared with transition-metal catalysis and photoredox catalysis, electro-organic decarboxylative transformations are considered as a green and sustainable protocol due to the absence of chemical oxidants and strong bases. Further, it exhibits good tolerance with various functional groups. In this Minireview, we summarize the recent advances and discoveries on the electrochemical decarboxylative transformations on C-C and C-heteroatoms bond formations.

Recent progress on electrochemical synthesis involving carboxylic acids

Carboxylic acids are not only essential sections of medicinal molecules, natural products and agrochemicals but also basic building blocks for organic synthesis. However, high temperature, expensive catalysts and excess oxidants are normally required for carboxylic acid group transformations. Therefore, more eco-friendly and efficient methods are urgently needed. Organic electrochemistry, as an environmentally friendly and sustainable synthetic method, can potentially avoid the above problems and is favored by more and more organic chemists. This review summarized the recent progress on the electrochemical synthesis of carboxylic acids to construct more complex compounds, emphasizing the development of electrosynthesis methodologies and mechanisms in order to attract more chemists to recognize the importance and applications of electrochemical synthesis.

Anodic Oxidation as an Enabling Tool for the Synthesis of Natural Products

Electrochemistry provides a valuable toolbox for organic synthesis and offers an appealing, environmentally benign alternative to the use of stoichiometric quantities of chemical oxidants or reductants. Its potential to control current efficiency along with providing alternative reaction conditions in a classical sense makes electrochemistry a suitable method for large-scale industrial transformations as well as for laboratory applications in the synthesis of complex molecular architectures. Even though research in this field has intensified over the recent decades, many synthetic chemists still hesitate to add electroorganic reactions to their standard repertoire, and hence, the full potential of preparative organic electrochemistry has not yet been unleashed. This short review highlights the versatility of anodic transformations by summarizing their application in natural product synthesis.

1 Introduction

2 Shono-Type Oxidation

3 C–N/N–N Bond Formation

4 Aryl–Alkene/Aryl–Aryl Coupling

5 Cycloadditions Triggered by Oxidation of Electron-Rich Arenes

6 Spirocycles

7 Miscellaneous Transformations

8 Future Prospects

Electrosynthesis Using Carboxylic Acid Derivatives: New Tricks for Old Reactions

Electrosynthetic organic chemistry is an old discipline that takes its root in Faraday's seminal works. The field has a rich history and is in the midst of a renaissance, due to the growing impetus of the chemical community to develop greener, more economical, and more efficient synthetic methodologies. Indeed, electrosynthesis relies on one of the greenest and cheapest reagents in the world: the electron itself. In this Account, the recent developments in the use of carboxylic acid derivatives in electrosynthesis are summarized. Until lately, the fate of the monoelectronic reduction of aromatic esters in nonprotic solvents remained unclear. Recent investigations have shown that aromatic esters are reduced and form surprisingly long-lived radical anions. Under the right conditions, these radical anions decompose into the corresponding carboxylates and alkyl radicals. These principles have been used to develop a novel electrochemical alcohol deoxygenation reaction using aromatic esters as stable and versatile radical precursors. In contrast to esters, the electrochemistry of carboxylic acids has been intensively studied. Pioneering works by Faraday and Kolbe in the late 1800s have revealed that the anodic oxidation of carboxylic acids leads to a radical decarboxylation. Interestingly, radical recombination is observed due to the very high concentration of radicals in the vicinity of the electrode. Such radical recombination is rarely observed during classical homogeneous radical reactions. The "Kolbe" reaction and its carbocationic variation have been intensively used across the fields due to their versatility. As we will develop in this Account, almost two hundred years after its discovery, the anodic decarboxylation of carboxylic acids is still relevant to modern organic chemists. For instance, we will examine how the non-decarboxylate Kolbe reaction of aromatic acids forms aroyloxy radicals and how oxycarbonyl radicals could be generated from hemioxalates. Finally, the carbocationic variant of the Kolbe reaction, known as the Hofer-Moest reaction, will be examined in the context of two newly developed reactions: a green MOM-type ether formation and the use of malonic acid derivatives as carbonyl synthons. Electrosynthesis is a powerful synthetic tool. Even if it might still be underutilized at the moment, there is little doubt that it will become one of the "classic" methods to activate small organic molecules in a very near future.

Electrochemically induced oxidative S–O coupling: synthesis of sulfonates from sulfonyl hydrazides and N-hydroxyimides or N-hydroxybenzotriazoles

A variety of sulfonates were synthesized from sulfonyl hydrazides and N-hydroxy compounds via electrochemically induced oxidative S–O bond formation.