Oxidative Coupling between Two Hydrocarbons: An Update of Recent C–H Functionalizations

The high utility of halogenated organic compounds has prompted the development of a vast number of transformations which install the carbon–halogen motif. Traditional routes to these building blocks have commonly involved multiple steps, harsh reaction conditions, and the use of stoichiometric and/or toxic reagents. In this regard, using transition metals to catalyze the synthesis of organohalides has become a mature field in itself, and applying these technologies has allowed for a decrease in the production of waste, higher levels of regio- and stereoselectivity, and the ability to produce enantioenriched target compounds. Furthermore, transition metals offer the distinct advantage of possessing a diverse spectrum of mechanistic possibilities which translate to the capability to apply new substrate classes and afford novel and difficult-to-access structures. This Review provides comprehensive coverage of modern transition metal-catalyzed syntheses of organohalides via a diverse array of mechanisms. Atte...

Modern Transition-Metal-Catalyzed Carbon–Halogen Bond Formation

Palladium-catalyzed aerobic oxidation reactions have been the focus of industrial application and extensive research efforts for nearly 60 years. A significant transition occurred in this field approximately 20 years ago, with the introduction of catalysts supported by ancillary ligands. The ligands play crucial roles in the reactions, including promotion of direct oxidation of palladium(0) by O2, bypassing the typical requirement for Cu salts or related redox cocatalysts to facilitate oxidation of the reduced Pd catalyst; facilitation of key bond-breaking and bond-forming steps during substrate oxidation; and modulation of chemo-, regio-, or stereoselectivity of a reaction. The use of ligands has contributed to significant expansion of the scope of accessible aerobic oxidation reactions. Increased understanding of the role of ancillary ligands should promote the development of new synthetic transformations, enable improved control over the reaction selectivity, and improve catalyst activity and stability...

Ligand-Promoted Palladium-Catalyzed Aerobic Oxidation Reactions

Computational investigations of ligand-directed selectivities in Ullmann-type coupling reactions of methanol and methylamine with iodobenzene by β-diketone- and 1,10-phenanthroline-ligated CuI complexes are reported. Density functional theory calculations using several functionals were performed on both the nucleophile formation and aryl halide activation steps of these reactions. The origin of ligand-directed selectivities in N- versus O-arylation reactions as described in a previous publication (J. Am. Chem. Soc. 2007, 129, 3490−3491) were studied and explained. The selectivities observed experimentally are derived not from initial CuI(nucleophile) complex formation but from the subsequent steps involving aryl halide activation. The arylation may occur via single-electron transfer (SET) or iodine atom transfer (IAT), depending on the electron-donating abilities of the ligand and nucleophile. Mechanisms involving either oxidative addition/reductive elimination or σ-bond metathesis are disfavored. SET mec...

Computational Explorations of Mechanisms and Ligand-Directed Selectivities of Copper-Catalyzed Ullmann-Type Reactions

π-Electron rich small molecule sensors for the recognition of nitroaromatics

1,3,5-Tri(1H-benzo[d]imidazol-2-yl)benzene derivatives, as a new kind of fluorescent chemosensor for the detection of nitroaromatic explosives, are designed and synthesized by simple N-hydrocarbylation. Among 16 obtained compounds, compound 4g has the best capability for detection of picric acid (PA), having good selectivity and high sensitivity. The detection of PA with 4g solution-coated paper strips at the picogram level is developed. A simple, portable, and low-cost method is provided for detecting PA in solution and contact mode.

Benzimidazole Derivatives: Selective Fluorescent Chemosensors for the Picogram Detection of Picric Acid

A highly efficient and mild palladium-catalyzed, one-pot, four-step cascade annulation has been developed to afford functionalized β- and γ-lactones in moderate to good yields with high regio- and diastereoselectivities in ionic liquids The employment of ionic liquids under mild reaction conditions makes this transformation green and practical Especially, this reaction provided a novel and convenient methodology for the construction of naturally occurring biologically active β- and γ-lactones

Palladium-catalyzed cascade annulation to construct functionalized β- and γ-lactones in ionic liquids.

A concise copper-catalyzed N–O bond cleavage/C–C/C–N bond formation procedure has been described for the synthesis of multisubstituted pyridines. Various oxime acetates, activated methylene compounds, and a wide range of aldehydes bearing aryl, heteroaryl, vinyl, and trifluoromethyl groups were employed to provide the tri- or tetrasubstituted pyridines with flexible substitution patterns. Moreover, this method features inexpensive catalysts, no need for extra oxidant, and high step-enconomy, which make it pratical and attractive.

Cu-Catalyzed Three-Component Cascade Annulation Reaction: An Entry to Functionalized Pyridines

Recent Advances in Pd-Catalyzed Cross-Coupling Reaction in Ionic Liquids

A copper-catalyzed aerobic oxidative reaction between aromatics or heteroaromatics with KSCN is developed by using O2 as the oxidant. The combination of Cu(OTf)2, N,N,N′,N′-tetramethylethylenediamine (TMEDA) and BF3·Et2O provides an efficient catalytic system, affording substituted thiocyanation products and 2-aminobenzothiazoles in excellent yields. The reaction also possesses a good functional group tolerance for both strong electron-withdrawing and electron-donating groups.

Jianxiao Li

Papers

Benzimidazole Derivatives: Selective Fluorescent Chemosensors for the Picogram Detection of Picric Acid

Palladium-catalyzed cascade annulation to construct functionalized β- and γ-lactones in ionic liquids.

Cu-Catalyzed Three-Component Cascade Annulation Reaction: An Entry to Functionalized Pyridines

Recent Advances in Pd-Catalyzed Cross-Coupling Reaction in Ionic Liquids

Copper-Catalyzed Aerobic Oxidative Regioselective Thiocyanation of Aromatics and Heteroaromatics