Copper-Catalyzed Radical Reductive Arylation of Styrenes with Aryl Iodides Mediated by Zinc in Water

Electroreductive deuteroarylation of alkenes enabled by an organo-mediator

Electroreduction mediated by organo-mediators has emerged as a concise and effective strategy, holding significant potential in the site-specific introduction of deuterium. In this study, we present an environmentally friendly electroreduction approach for anti-Markovnikov selective deuteroarylation of alkenes and aryl iodides with D2O as the deuterium source. The key to the protocol lies in the employment of a catalytic amount of 2,2'-bipyiridine as an efficient organo-mediator, which facilitates the generation of aryl radicals by assisting in the cleavage of the C-X (X = I or Br) bonds in aryl halides. Because its reduction potential matches that of aryl iodides, the organo-mediator can control the chemoselectivity of the reaction and avoid the side reactions of competitive substrate deuteration. These phenomena are theoretically supported by CV experiments and DFT calculations. Our protocol provides a series of mono-deuterated alkylarenes with excellent deuterium incorporation through two single-electron reductions (SER), without requiring metal catalysts, external reductants, and sacrificial anodes.

Transition-Metal-Free Anti-Markovnikov Hydroarylation of Alkenes with Aryl Chlorides through Consecutive Photoinduced Electron Transfer

The hydroarylation of alkenes has emerged as a powerful strategy for arene functionalization. However, aryl chlorides remain a large challenge in this type of reaction due to the chemical inertness of the C(sp2)-Cl bond and high negative reduction potential. Herein, we report an anti-Markovnikov radical hydroarylation of alkenes with aryl chlorides via visible-light photoredox catalysis. The key reactive aryl radicals can be efficiently achieved from aryl chlorides by consecutive photoinduced electron transfer. This transition-metal-free protocol features mild conditions, a wide substrate scope, and functional group tolerance, producing a diverse range of linear alkylarenes in moderate to good yields. The reaction is proposed to proceed through a radical-polar crossover pathway.

2-Methoxyethyl Nitrite as a Reagent for Chemoselective On-Water Nitration

An on-water approach has been developed that allows a nitration of tyrosines and phenols under mild conditions. We envisioned that the assembly of tyrosine/tyrosyl radical couples with interfacial water molecules would realize a biomimetic stacking hydrogen atom transfer (HAT) transition state to facilitate the electron-transfer process. The optimal organic nitrite, 2-methoxyethyl nitrite, resulted in rapid coupling of the tyrosyl radicals with •NO 2 at the oil-water interface to afford the nitrated phenols. Many characteristics found in our on-water strategy are distinct from other complementary systems that include radical nitration. These enticing roles of water in the reaction process introduce new avenues to explore in the design of synthetic organic chemistry systems.

Generation of aryl radicals by redox processes. Recent progress in the arylation methodology

Arylation methods based on the generation and use of aryl radicals have been a rapidly growing field of research in recent years and currently represent a powerful strategy for carbon – carbon and carbon – heteroatom bond formation. The progress in this field is related to advances in the methods for generation of aryl radicals. The currently used aryl radical precursors include aryl halides, aryldiazonium and diaryliodonium salts, arylcarboxylic acids and their derivatives, arylboronic acids, arylhydrazines, organosulfur(II, VI) compounds and some other compounds. Aryl radicals are generated under mild conditions by single electron reduction or oxidation of precursors induced by conventional reagents, visible light or electric current. A crucial role in the development of the radical arylation methodology belongs to photoredox processes either catalyzed by transition metal complexes or organic dyes or proceeding without catalysts. Unlike the conventional transition metal-catalyzed arylation methods, radical arylation reactions proceed very often at room temperature and have high functional group tolerance. Without claiming to be exhaustive, this review covers the most important advances of the current decade in the generation and synthetic applications of (het)aryl radicals. Examples of reactions are given and mechanistic insights are highlighted.

The bibliography includes 341 references.

Iron-Catalyzed Conjugate Addition of Aryl Iodides onto Activated Alkenes under Air in Water

The combination of commercially available FeCl3·6H2O with a water-soluble cationic 2,2′-bipyridyl catalytic system was found to enable the direct conjugate addition of aryl iodides onto activated alkenes, such as an α,β-unsaturated ester and a ketone, in a weakly acidic aqueous solution. This operationally simple protocol was carried out at 80 °C under air atmosphere in a potassium acetate-buffered aqueous solution for 12 h in the presence of Zn dust as a reductant to provide the desired 1,4-adducts in good yields.

"Bulky-Yet-Flexible" α-Diimine Palladium-Catalyzed Reductive Heck Cross-Coupling: Highly Anti-Markovnikov-Selective Hydroarylation of Alkene in Air

To pursue a highly regioselective and efficient reductive Heck reaction, a series of moisture- and air-stable α-diimine palladium precatalysts were rationally designed, readily synthesized, and fully characterized. The relationship between the structures of the palladium complexes and the catalytic properties was investigated. It was revealed that the"bulky-yet-flexible"palladium complexes allowed highly anti-Markovnikov-selective hydroarylation of alkenes with (hetero)aryl bromides under aerobic conditions. Further synthetic application of the present protocol could provide rapid and straightforward access to functional and biologically active molecules.

Radical cyclizations of enynes/dienes with alcohols in water using a green oxidant

A simple, eco-friendly, and efficient methodology for performing radical cyclizations of enynes/dienes with alcohols in water has been established.

Nickel(II)-Catalyzed [5 + 1] Annulation of 2-Carbonyl-1-propargylindoles with Hydroxylamine To Synthesize Pyrazino[1,2-a]indole-2-oxides in Water

An atom-economical and practical method for the efficient synthesis of various pyrazino[1,2-a]indole-2-oxides was developed through a nickel(II)-catalyzed [5 + 1] annulation of 2-carbonyl-1-propargylindoles with hydroxylamine in water without using an organic solvent. The reaction involved an initial condensation of 2-carbonyl-1-propargylindoles with hydroxylamine to afford oxime intermediates, which then underwent a nickel(II)-catalyzed 6-exo-dig cyclization. Preliminary studies showed that (n-Bu)₄NI served as a phase transfer catalyst and promoted the formation of active nickel(II) species. More importantly, the nickel(II) salt and phase transfer catalyst-in-water could be recycled seven times, and a gram scalable product was easily obtained in good yields through a filtration and washing protocol.