In this contribution, we provide a comprehensive overview of C-H activation methods promoted by NHC-transition metal complexes, covering the literature since 2002 (the year of the first report on metal-NHC-catalyzed C-H activation) through June 2019, focusing on both NHC ligands and C-H activation methods. This review covers C-H activation reactions catalyzed by group 8 to 11 NHC-metal complexes. Through discussing the role of NHC ligands in promoting challenging C-H activation methods, the reader is provided with an overview of this important area and its crucial role in forging carbon-carbon and carbon-heteroatom bonds by directly engaging ubiquitous C-H bonds.

N-Heterocyclic Carbene Complexes in C–H Activation Reactions

Functionalized biaryl-containing motifs are among the most valuable synthetic scaffolds in organic chemistry with wide ranging commercial applications in pharmaceuticals, functional materials, and agrochemicals. Recently, there has been tremendous progress in the development of methods for functional-group-tolerant, cost-effective, and atom-economic ruthenium-catalyzed C–H arylation, providing attractive catalytic alternatives to traditional C–H functionalization and cross-coupling approaches. New ruthenium-catalyzed C–H arylation reactions have resulted in the development of attractive and highly efficient synthetic approaches to functionalized biaryls unavailable by other methods. New mechanistic manifolds have emerged, thus opening prospects for the development of a broad range of novel reactions. Strategies for the use of ruthenium catalysis in complex synthesis, including industrial applications, have been reported, validating the synthetic potential of this mode of reactivity. The development of new...

Recent Developments in Ruthenium-Catalyzed C–H Arylation: Array of Mechanistic Manifolds

It is textbook knowledge that carboxamides benefit from increased stabilisation of the electrophilic carbonyl carbon when compared to other carbonyl and carboxyl derivatives This results in a considerably reduced reactivity towards nucleophiles Accordingly, a perception has been developed of amides as significantly less useful functional handles than their ester and acid chloride counterparts However, a significant body of research on the selective activation of amides to achieve powerful transformations under mild conditions has emerged over the past decades This review article aims at placing electrophilic amide activation in both a historical context and in that of natural product synthesis, highlighting the synthetic applications and the potential of this approach

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Amide activation: an emerging tool for chemoselective synthesis

This review surveys recent progress in the chemistry of polycyclic heteroaromatic molecules with a focus on structural diversity and synthetic methodology. The article covers literature published during the period of 2016-2020, providing an update to our first review of this topic (Chem. Rev.2017, 117 (4), 3479-3716).

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds.

Recent Advances in Ruthenium(II)-Catalyzed C−H Bond Activation and Alkyne Annulation Reactions

Expedient synthesis of new cinnoline diones by Ru-catalyzed regioselective unexpected deoxygenation-oxidative annulation of propargyl alcohols with phthalazinones and pyridazinones

Palladium(II)/N-Heterocyclic Carbene-Catalyzed Direct C-H Acylation of Heteroarenes with N-Acylsaccharins.

A Ru(II)-catalyzed C–H arylation approach has been developed utilizing β-carboline alkaloids as the directing group. Selective formations of diarylated products from moderate to excellent yields were accomplished. Broad substrate scope with excellent functional group tolerance for C1-phenyl/thienyl/PAHs-β-carbolines was demonstrated. X-ray crystal structure of cycloruthenated complex 2cr and no arylation reaction with model substrate 13 strongly suggests that N2 is the directing group than N9 in C1-aryl-β-carbolines. Catalytic properties and stability of the cycloruthenated complexes have been explored. Library of biologically relevant new β-carboline derivatives and isolation of its cycloruthenated intermediates are the highlights of this work.

Ru(II)-Catalyzed β-Carboline Directed C–H Arylation and Isolation of Its Cycloruthenated Intermediates

Rationally designed fluorene-based mono- and bimetallic Pd–PEPPSI complexes were synthesized and demonstrated to be effective for the one-pot sequential α-arylation/alkylation of oxindoles. This streamlined approach offers efficient access to functionalized 3,3-disubstituted oxindoles in excellent yields (up to 89%) under mild reaction conditions.

Palladium(II)/N-Heterocyclic Carbene Catalyzed One-Pot Sequential α-Arylation/Alkylation: Access to 3,3-Disubstituted Oxindoles.

Monometallic and bimetallic palladium(II)/N-heterocyclic carbene complexes appended with naphthalimide or bisnaphthalimide moieties were designed, synthesized, and characterized. Employment of these catalysts brings about the step-economic and regioselective heteroannulation of tertiary propargyl alcohols with o-haloanilines resulting in biologically and pharmaceutically relevant 2-alkenylindoles. Basis for the regioselective heteroannulation is unraveled by coordination of the propargylic hydroxy moiety to palladium during insertion. Embracing this methodology, a single regioisomer of unsymmetrical 2,3-disubstituted indoles could be achieved through late-stage modification. The role of the naphthalimide or bisnaphthalimide appended to the NHC on the catalytic efficiency has been studied.

Palladium(II)/N‐Heterocyclic Carbene‐Catalyzed Regioselective Heteroannulation of Tertiary Propargyl Alcohols and o‐Haloanilines to form 2‐Alkenylindoles

Thirumanavelan Gandhi

Papers

Expedient synthesis of new cinnoline diones by Ru-catalyzed regioselective unexpected deoxygenation-oxidative annulation of propargyl alcohols with phthalazinones and pyridazinones

Palladium(II)/N-Heterocyclic Carbene-Catalyzed Direct C-H Acylation of Heteroarenes with N-Acylsaccharins.

Ru(II)-Catalyzed β-Carboline Directed C–H Arylation and Isolation of Its Cycloruthenated Intermediates

Palladium(II)/N-Heterocyclic Carbene Catalyzed One-Pot Sequential α-Arylation/Alkylation: Access to 3,3-Disubstituted Oxindoles.

Palladium(II)/N‐Heterocyclic Carbene‐Catalyzed Regioselective Heteroannulation of Tertiary Propargyl Alcohols and o‐Haloanilines to form 2‐Alkenylindoles