Heterogenized Phenanthroline-Pd(2+)-Catalyzed Alkoxycarbonylation of Aryl Iodides in Base-Free Conditions

Visible-Light-Induced Divergent Oxygenation of Methylbenzene Utilizing Aryl Halides

The selective oxidation of methylbenzene to value-added products is of indisputable importance in organic synthesis. Although photocatalytic oxidation reactions of toluene have achieved great success for the preparation of its oxidative products, such as carboxylic acids, benzaldehyde, and benzoate, there remains a lack of a unified photocatalytic system for the selective preparation of these oxidation products. Herein, we report a metal- and additive-free photocatalytic protocol enabled by aryl halides using O2 as a green oxidant for the selective synthesis of the above-mentioned three oxidation products by adjusting the reaction solvent. This strategy features many advantages, including environmentally friendly and mild reaction conditions, broad substrate applicability and functional group tolerance, and potential practical application for the synthesis of aromatic carboxylic drugs and polymer materials and degradation of polystyrene waste. The continuous-flow system was utilized for the oxidation of toluene, which resulted in a reduced reaction time and increased production efficiency. Detailed mechanistic investigation revealed that the hydrogen atom transfer process was facilitated by the bromine radical from aryl halides for further oxidation, and an electron donor-acceptor complex of methylbenzene and aryl halides may exist.

Low-Valent Tungsten Catalyzed Carbonylative Synthesis of Benzoates from Aryl Iodides and Alcohols

Non-noble metals catalyzed carbonylative reactions serve as straightforward and sustainable methods for the synthesis of functionalized carbonyl-containing compounds. Herein, a low-valent-tungsten-catalyzed reaction that enables the coupling of aryl iodides and alcohols or phenols was disclosed, employing the readily available W(CO)6 as the effective catalyst and PPh3 as ligand. Under the optimal reaction conditions, aryl iodides smoothly underwent carbonylative coupling reactions with alcohols or phenols, processing the feature of broad substrate scope and good functional groups tolerance. Furthermore, this conversion can be carried out on a gram scale, showcasing significant promise in the synthesis of pharmaceutical or biologically active compounds.

Electrochemically Driven Nickel-Catalyzed Halogenation of Unsaturated Halide and Triflate Derivatives

A robust electrochemically driven nickel-catalyzed halogen exchange of unsaturated halides and triflates (Br to Cl, I to Cl, I to Br, and OTf to Cl) is reported. A combination of NiCl2  ⋅ glyme as the precatalyst, 2,2'-bipyridine as a ligand, NMP as the solvent, and electrochemistry allowed the generation of a nickel species that promotes reductive elimination of the desired product. This paired electrochemical halogenation is compatible with a range of unsaturated halides and triflates, including heterocycles, dihaloarenes, and alkenes with good functional-group tolerance. Joint experimental and theoretical mechanistic investigations highlighted three catalytic events: i) oxidative addition of the aryl halide to a Ni(0) species to deliver a Ni(II) intermediate; ii) halide metathesis at Ni(II); iii) electrochemical oxidation of Ni(II) to Ni(III) to enable the formation of the desired aryl halide upon reductive elimination. This methodology allows the replacement of heavy halogens (I or Br) or polar atoms (O) with the corresponding lighter and more lipophilic Cl group to block undesired reactivity or modify the properties of drug and agrochemical candidates.