Nickel-Catalyzed Amination of Aryl 2-Pyridyl Ethers via Cleavage of the Carbon–Oxygen Bond

A Second-Generation Palladacycle Architecture Bearing a N-Heterocyclic Carbene and Its Catalytic Behavior in Buchwald–Hartwig Amination Catalysis

Palladacyclic architectures have been shown as versatile motifs in cross-coupling reactions. NHC-ligated palladacycles possessing unique electronic and steric properties have helped to stabilize the catalytically active species and provide additional control over reaction selectivity. Here, we report on a synthetic protocol leading to palladacycle complexes using a mild base and an environmentally desirable solvent, with a focus on complexes bearing backbone-substituted N-heterocyclic carbene ligands. The readily accessible complexes exhibit high catalytic activity in the Buchwald–Hartwig amination. This is achieved using low catalyst loading and mild reaction conditions in a green solvent.

Ru(II)-Catalyzed Difunctional Pyridyloxy-Directed Regio- and Stereospecific Addition of Carboxylic Acids to Internal Alkynes

A highly efficient Ru(II)-catalyzed regio- and stereospecific hydro-oxycarbonylation of unsymmetrical internal alkynes bearing a difunctional 2-pyridyloxy directing group with carboxylic acids has been developed, which provides allylic (Z)-enol esters in good to excellent yields with a broad substrate scope under mild conditions. The difunctional directing group can be diversely derivatized, particularly undergoing allylic substitution with various nucleophiles to afford β-functionalized (Z)-enol esters without directing groups.

Nickel-Catalyzed Cross-Coupling of Aryl 2-Pyridyl Ethers with Organozinc Reagents: Removal of the Directing Group via Cleavage of the Carbon-Oxygen Bonds

Reaction of aryl 2-pyridyl ethers with arylzinc reagents under catalysis of NiCl₂(PCy₃)₂ affords aryl-aryl cross-coupling products via selective cleavage of C_Ar-OPy bonds. The reaction features a wide substrate range and good compatibility of functional groups. β-H-free alkylzinc reagents are also applicable as the nucleophiles in the transformation, whereas β-H-containing alkylzinc reagents lead to a mixture of cross-coupling and hydrogenation products.

N-Arylation of (hetero)arylamines using aryl sulfamates and carbamates via C–O bond activation enabled by a reusable and durable nickel(0) catalyst

An effective and general aryl amination protocol has been developed using a magnetically recoverable Ni(0) based nanocatalyst.

meta C-H Arylation of Electron-Rich Arenes: Reversing the Conventional Site Selectivity

Controlling site selectivity of C-H activation without using a directing group remains a significant challenge. While Pd(II) catalysts modulated by a mutually repulsive pyridine-type ligand have been shown to favor the relatively electron-rich carbon centers of arenes, reversing the selectivity to favor palladation at the relatively electron-deficient positions has not been possible. Herein we report the first catalytic system that effectively performs meta C-H arylation of a variety of alkoxy aromatics including 2,3-dihydrobenzofuran and chromane with exclusive meta site selectivity, thus reversing the conventional site selectivity governed by native electronic effects. The identification of an effective ligand and modified norbornene (NBE-CO₂Me), as well as taking advantage of the statistics, are essential for achieving the exclusive meta selectivity.

Sequential Functionalization of meta-C-H and ipso-C-O Bonds of Phenols

The use of a template as a linchpin motif in directed remote C-H functionalization is a versatile yet relatively underexplored strategy. We have developed a template-directed approach to realizing one-pot sequential palladium-catalyzed meta-selective C-H olefination of phenols, and nickel-catalyzed ipso-C-O activation and arylation. Thus, this bifunctional template converts phenols to synthetically useful 1,3-disubstituted arenes.

A comprehensive overview of directing groups applied in metal-catalysed C-H functionalisation chemistry

The present review is devoted to summarizing the recent advances (2015-2017) in the field of metal-catalysed group-directed C-H functionalisation. In order to clearly showcase the molecular diversity that can now be accessed by means of directed C-H functionalisation, the whole is organized following the directing groups installed on a substrate. Its aim is to be a comprehensive reference work, where a specific directing group can be easily found, together with the transformations which have been carried out with it. Hence, the primary format of this review is schemes accompanied with a concise explanatory text, in which the directing groups are ordered in sections according to their chemical structure. The schemes feature typical substrates used, the products obtained as well as the required reaction conditions. Importantly, each example is commented on with respect to the most important positive features and drawbacks, on aspects such as selectivity, substrate scope, reaction conditions, directing group removal, and greenness. The targeted readership are both experts in the field of C-H functionalisation chemistry (to provide a comprehensive overview of the progress made in the last years) and, even more so, all organic chemists who want to introduce the C-H functionalisation way of thinking for a design of straightforward, efficient and step-economic synthetic routes towards molecules of interest to them. Accordingly, this review should be of particular interest also for scientists from industrial R&D sector. Hence, the overall goal of this review is to promote the application of C-H functionalisation reactions outside the research groups dedicated to method development and establishing it as a valuable reaction archetype in contemporary R&D, comparable to the role cross-coupling reactions play to date.

Nickel-catalyzed C-O bond reduction of aryl and benzyl 2-pyridyl ethers

The reduction of aryl and benzyl 2-pyridyl ethers with sodium isopropoxide was carried out via nickel-catalyzed C-OPy bond cleavage, giving reductive products in reasonable to excellent yields. This method allowed the 2-pyridyloxy group to be directly removed with high efficiency, mild reaction conditions, and good compatibility of functional groups.

Efficient and selective hydrogenation of C–O bonds with a simple sodium formate catalyzed by nickel

A Ni-catalyzed hydrogenation of C–O compounds with sodium formate is developed. Various esters, i.e. aryl, alkenyl, benzyl pivalates, and even the aryl ethers, were efficiently reduced with a loading of nickel catalysts down to 0.5 mol%.