Rhodaelectro-Catalyzed peri-Selective Direct Alkenylations with Weak O-Coordination Enabled by the Hydrogen Evolution Reaction (HER)

Electrochemical Enantioselective C-H Annulation by Achiral Rhodium(III)/Chiral Brønsted Base Domino Catalysis

Rhodium(III)-catalyzed enantioselective C-H activation has emerged as a powerful tool for assembling enabling chiral molecules. However, this approach is significantly hampered by the cumbersome synthetic routes for preparing chiral rhodium catalysts. In sharp contrast, we herein report on an electrochemical domino catalysis system that exploits an achiral Cp*-rhodium catalyst along with an easily accessible chiral Brønsted base for an enantioselective C-H activation/annulation reaction of alkenes by benzoic acids. Our strategy offers an environmentally benign and most user-friendly approach for assembling synthetically useful chiral phthalides in good enantioselectivity, employing electricity as the sustainable oxidant.

Visible Light-Promoted Regioselective Benzannulation of Vinyl Sulfoxonium Ylides with Ynoates

Herein, we report a highly regioselective [4 + 2]-annulation of vinyl sulfoxonium ylides with ynoates under light-mediated conditions. The reaction proceeds through the new dienyl sulfoxonium ylide, which undergoes photolysis under blue light irradiation to give highly substituted naphthalene scaffolds. The method presented here operates at room temperature and does not require the addition of an external photosensitizer. The in situ-generated dienyl sulfoxonium ylide absorbs light and acts as a photosensitizer for the formation of arenes. The synthetic potential of these benzannulations was further illustrated by various synthetic transformations and a scale-up reaction. Moreover, control experiments and quantum chemical calculations reveal the mechanistic details of the developed reaction.

Electrochemical N-Aroylation of Sulfoximines by Using Benzoyl Hydrazines with H2 Generation

Developed here is a robust electrochemical cross-coupling reaction between aroyl hydrazine and NH-sulfoximine via concomitant cleavage and formation of C(sp2 )-N bonds with the evolution of H2 and N2 as innocuous by-products. This sustainable protocol avoids the use of toxic reagents and occurs at room temperature. The reaction proceeds via the generation of an aroyl and a sulfoximidoyl radical via anodic oxidation under constant current electrolysis (CCE), affording N-aroylated sulfoximine. The strategy is applied to late-stage sulfoximidation of L-menthol, (-)-borneol, D-glucose, vitamin-E derivatives, and marketed drugs such as probenecid, ibuprofen, flurbiprofen, ciprofibrate, and sulindac. In addition, the present methodology is mild, high functional group tolerance with broad substrate scope and scalable.

The crucial role of silver(I)-salts as additives in C-H activation reactions: overall analysis of their versatility and applicability

Transition-metal catalyzed C-H activation reactions have been proven to be useful methodologies for the assembly of synthetically meaningful molecules. This approach bears intrinsic peculiarities that are important to be studied and comprehended in order to achieve its best performance. One example is the use of additives for the in situ generation of catalytically active species. This strategy varies according to the type of additive and the nature of the pre-catalyst that is being used. Thus, silver(I)-salts have proven to play an important role, due to the resulting high reactivity derived from the pre-catalysts of the main transition metals used so far. While being powerful and versatile, the use of silver-based additives can raise concerns, since superstoichiometric amounts of silver(I)-salts are typically required. Therefore, it is crucial to first understand the role of silver(I) salts as additives, in order to wisely overcome this barrier and shift towards silver-free systems.

Transition Metal-Catalyzed C-H Functionalization Through Electrocatalysis

Electrochemically promoted transition metal-catalyzed C-H functionalization has emerged as a promising area of research over the last few decades. However, development in this field is still at an early stage compared to traditional functionalization reactions using chemical-based oxidizing agents. Recent reports have shown increased attention on electrochemically promoted metal-catalyzed C-H functionalization. From the standpoint of sustainability, environmental friendliness, and cost effectiveness, electrochemically promoted oxidation of a metal catalyst offers a mild, efficient, and atom-economical alternative to traditional chemical oxidants. This Review discusses advances in the field of transition metal-electrocatalyzed C-H functionalization over the past decade and describes how the unique features of electricity enable metal-catalyzed C-H functionalization in an economic and sustainable way.

Molecular Engineering of Chalcogen-Embedded Anthanthrenes via peri-Selective C-H Activation: Fine-Tuning of Crystal Packing for Organic Field-Effect Transistors

Disclosed herein is a RhCl₃ -catalyzed peri-selective C-H/C-H oxidative homo-coupling of 1-substituted naphthalenes, which provides a highly efficient and streamlined approach to chalcogen-embedded anthanthrenes from readily available starting materials. Introducing O, S, and Se into the anthanthrene skeleton leads to gradually increased π-π stacking distances but significantly enhanced π-π overlaps with the growth of the hetero-atom radius. Moderate π-π distance, overlap area, and intermolecular S-S interactions endow S-embedded anthanthrene (PTT) with excellent 2D charge-transport properties. Moreover, the transformation of p-type to n-type S-embedded anthanthrenes is realized for the first time via the S-atom oxidation from PTT to PTT-O4. In organic field-effect transistor devices, PTT derivatives exhibit hole transport with mobilities up to 1.1 cm²  V^-1  s^-1 , while PTT-O4 shows electron transport with a mobility of 0.022 cm²  V^-1  s^-1 .

Electrochemical Amidation: Benzoyl Hydrazine/Carbazate and Amine as Coupling Partners

An electrochemical amidation of benzoyl hydrazine/carbazate and primary/secondary amine as coupling partners via concomitant cleavage and formation of C(sp²)-N bonds has been achieved. This methodology proceeds under metal-free and exogenous oxidant-free conditions producing N₂ and H₂ as byproducts. Mechanistic studies reveal the in situ generations of both acyl and N-centered radicals from benzoyl hydrazines and amines. The utility of this protocol is demonstrated through a large-scale, and synthesis of bezafibrate, a hyperlipidemic drug.

Electricity Induced Rhodium-Catalyzed Oxidative C-H/N-H Annulation of Alkynes with Arylhydrophthalazinediones

The development of stoichiometric oxidant-free regioselective annulation protocol is a challenging aspect in organic synthesis. Herein, we disclose electricity as a greener oxidant for the C-H/N-H annulation to construct cinnolines using rhodium(III) catalyst under mild conditions. A detailed mechanistic investigation revealed the possibility of both Rh(III/I) and Rh(III/IV) catalytic cycles for the formation of annulated product. Exclusive regioselectivity, diverse substrate scope, and commercially available cheap graphite electrodes are key features of this protocol.

Non-directed Pd-catalysed electrooxidative olefination of arenes

The Fujiwara–Moritani reaction is a powerful tool for the olefination of arenes by Pd-catalysed C–H activation. However, the need for superstoichiometric amounts of toxic chemical oxidants makes the reaction unattractive from an environmental and atom-economical view. Herein, we report the first non-directed and regioselective olefination of simple arenes via an electrooxidative Fujiwara–Moritani reaction. The versatility of this operator-friendly approach was demonstrated by a broad substrate scope which includes arenes, heteroarenes and a variety of olefins. Electroanalytical studies suggest the involvement of a Pd(ii)/Pd(iv) catalytic cycle via a Pd(iii) intermediate.

The Fujiwara–Moritani reaction using electric current is a powerful tool for the olefination of arenes by Pd-catalysed C–H activation.