An Approach to Five-Membered Lactams from Aliphatic Amides and Terminal Acetylenes by Nickel Catalysis

Transition-Metal-Catalyzed, Coordination-Assisted Functionalization of Nonactivated C(sp3)-H Bonds

Transition-metal-catalyzed, coordination-assisted C(sp³)-H functionalization has revolutionized synthetic planning over the past few decades as the use of these directing groups has allowed for increased access to many strategic positions in organic molecules. Nonetheless, several challenges remain preeminent, such as the requirement for high temperatures, the difficulty in removing or converting directing groups, and, although many metals provide some reactivity, the difficulty in employing metals outside of palladium. This review aims to give a comprehensive overview of coordination-assisted, transition-metal-catalyzed, direct functionalization of nonactivated C(sp³)-H bonds by covering the literature since 2004 in order to demonstrate the current state-of-the-art methods as well as the current limitations. For clarity, this review has been divided into nine sections by the transition metal catalyst with subdivisions by the type of bond formation. Synthetic applications and reaction mechanism are discussed where appropriate.

Bidentate Directing Groups: An Efficient Tool in C-H Bond Functionalization Chemistry for the Expedient Construction of C-C Bonds

During the past decades, synthetic organic chemistry discovered that directing group assisted C-H activation is a key tool for the expedient and siteselective construction of C-C bonds. Among the various directing group strategies, bidentate directing groups are now recognized as one of the most efficient devices for the selective functionalization of certain positions due to fact that its metal center permits fine, tunable, and reversible coordination. The family of bidentate directing groups permit various types of assistance to be achieved, such as N,N-dentate, N,O-dentate, and N,S-dentate auxiliaries, which are categorized based on the coordination site. In this review, we broadly discuss various C-H bond functionalization reactions for the formation of C-C bonds with the aid of bidentate directing groups.

Merging Cu-catalysed C–H functionalisation and intramolecular annulations: computational and experimental studies on an expedient construction of complex fused heterocycles

A copper-catalysed protocol for the synthesis of fused dihydrobenzofuran-isoquinolone compounds through an intramolecular annulation of readily accessible benzamide substrates is reported, along with a full DFT study into the mechanism.

Nickel-catalyzed oxidative C-H/N-H annulation of N-heteroaromatic compounds with alkynes

The reaction of N-heteroaromatic compounds, such as 2-aryl-pyrrole, benzimidazole, imidazole, indole, and pyrazole derivatives, with alkynes in the presence of a catalytic amount of a nickel complex results in C-H/N-H oxidative annulation. The reaction shows a high functional group compatibility. While both Ni(0) and Ni(ii) complexes show a high catalytic activity, Ni(0) is proposed as a key catalytic species in the main catalytic cycle. In the case of the Ni(ii) system, the presence of a catalytic amount of a strong base, such as KOBu t , is required for the reaction to proceed. In sharp contrast, a base is not required in the case of the Ni(0) system. The proposed mechanism is supported by DFT studies.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

Propargylation of Ugi Amide Dianion: An Entry into Pyrrolidinone and Benzoindolizidine Alkaloid Analogues

Propargylation of Ugi adducts under the addition of excess sodium hydride in DMSO leads to direct formation of pyrrolidinone enamides, which are useful precursors of iminium intermediates and may be trapped by various nucleophiles. This approach has been applied to the formation of benzoindolizidine alkaloids with high diversity via a Ugi/propargylation/Pictet-Spengler cyclization.

Nickel catalyzed site selective C–H functionalization of α-aryl-thioamides

A nickel catalyzed C–H bond functionalization reaction has been used for the first time to study an intramolecular site-selective C–S bond formation of arenes.

Nickel(ii)-catalyzed tandem C(sp2)–H bond activation and annulation of arenes with gem-dibromoalkenes

A nickel(ii)/silver(i)-catalyzed tandem C(sp²)–H activation and intramolecular annulation of arenes with dibromoalkenes has been successfully achieved, which offers an efficient approach to the 3-methyleneisoindolin-1-one scaffold. Attractive features of this system include its low cost, ease of operation, and its ability to access a wide range of isoindolinones.

A nickel(ii)/silver(i)-catalyzed tandem C(sp²)–H activation and intramolecular annulation of arenes with dibromoalkenes has been successfully achieved, which offers an efficient approach to the 3-methyleneisoindolin-1-one scaffold.

Accessing pyrrolones and pyridinones: controlling 5-exo and 6-endo ring closures in heterocyclic alkynylamides

Competitive 5-exo and 6-endo anionic intramolecular cyclization reactions in heterocyclic alkynylamides were explored via experimental and computational analysis. The 5-exo-dig cyclization pathway is usually disfavoured in heterocyclic systems, and 6-endo products are often both the kinetic and thermodynamic products. However, we’ve found that it is possible to shift selectivity toward the 5-exo-dig pyrrolone products away from the less strained pyridinone products that are produced via the 6-endo-dig cyclization. Parameters such as identity of heteroatom, heteroatom positioning within the heterocycle, and functionality on the alkyne were investigated and, in many cases, were found to strongly influence product ratios. A series of computational studies was performed to provide further insight into the 5-exo-dig and 6-endo-dig pathways in these heterocyclic systems. Theoretical predictions were found to reproduce experimental results, highlighting the predictive capabilities of the computations in determining preferred products.

Cobalt-promoted selective arylation of benzamides and acrylamides with arylboronic acids

A novel cobalt-promoted arylation of aryl C–H bonds with arylboronic acids has been realized by using 8-aminoquinoline as the directing group. A notable feature of this newly developed protocol is that acrylamides, which cannot be arylated using copper salts as the promoter, can also be efficiently arylated.