Themed collection Functionalization of unreactive C-H bonds

This highlight describes an emerging trend in the C–H activation field: the use of the cyclometallated catalysts for the challenging and unprecedented direct transformations.

This article presents “state of art” trends in achieving the bidentate auxiliary assisted distal sp³ C–H functionalization beyond proximal sites. The substrate scope and mechanistic underpinnings of the key methodologies are highlighted.

This review systematically discusses all of the visible light-induced functionalization methodologies and mechanisms of two significant heterocycles, indazole and pyrazole.

This feature review is focused on recent key applications of commonly used transition-metal Cp-type catalysts for C–H bond functionalizations.

Advancements in the palladium-catalyzed functionalization of diastereotopic or prochiral C(sp³)–H bonds generating stereogenic centers and stereo-arrays in aliphatic compounds have been highlighted.

Merging two powerful methodologies, metallaphoto-catalyzed benzylic and allylic C(sp³)–H bond functionalizations provide a series of general and mild approaches for diversification of alkylbenzenes and alkenes.

Recent advances on non-precious metal-catalyzed C–H functionalization of N-heteroarenes are discussed.

Synthesis of air-stable PNN iron pincer complexes and their application in the C–H borylation of arenes.

The oxidative coupling between two carbon–hydrogen (C–H) bonds offers the most straightforward pathway to construct C–C bonds from hydrocarbons without pre-functionalization, exhibiting high step- and atom-economy.

Over the past two decades, the C–H bond activation and functionalization reaction has been known as a prevailing method for the construction of carbon–carbon and carbon–heteroatom bonds using various transition metal catalysts.

Pd-Catalyzed and ligand-enabled difunctionalization of olefins through the unreactive C–H bond functionalization of either alkene or their respective coupling partners was summarized.

exo-Metallacycles have become the key reaction intermediates in activating various remote C(sp²)–H and C(sp³)–H bonds in the past decade and aided in achieving unusual site-selectivity.

Visible light mediated functionalizations have significantly expanded the scope of alkynes by unraveling new mechanistic pathways and enabling their transformation to diverse structural entities.

Transition metal-assisted remote C–H bond activation at the non-classical reaction sites of various olefinic substrates with the aid of a chain-walking process is depicted in this feature article.

Over the last decade, high-valent cobalt catalysis has earned a place in the spotlight as a valuable tool for C–H activation and functionalization.

The conversion of light alkanes into bulk chemicals is becoming an important challenge as it effectively avoids the use of prefunctionalized alkylating reagents.

Exogenous-directing-group free C–H acetoxylation of hydrocinnamic and phenylacetic acid derivatives is reported.

The bisulfate ligand within a reported vanadium (V) electrocatalyst serves as the active site for CH₄ functionalization. Activity decreases if the bisulfate ligand is substituted with a redox-inactive dihydrogen phosphate.

Cobalt(II)-catalyzed oxidative annulation of hydrazones with heterobicyclic alkenes has been accomplished for accessing functionalized indane derivatives under aerobic conditions.

We report a regioselective remote difunctionalization of unreactive C–H bonds of 2H-indazoles with Koser's reagents to provide C-4,7 substituted 2H-indazole derivatives.

The use of Pd(OAc)₂ catalyst and AgOAc oxidant enabled the direct regioselective oxidative C–H/C–H cross-coupling of pyrazolo[1,5-a]azineswith various five-membered heteroarenes without the need of pre-activation and/or directing groups.

The C–H bond addition reaction of 2-phenylpyridine derivatives with α,β-unsaturated carboxylic acids catalyzed by Cp*Rh(III)/BH₃·SMe₂ is reported.

An iron-catalysed C–H functionalisation of simple monosubstituted allenes for the synthesis of 1-tetrahydroisoquinolinyl 1,1-disubstituted allenes is reported.

An efficient visible organophotoredox-catalyzed redox-neutral radical cascade involving allenamides and alkyl N-(acyloxy)phthalimides allowing the synthesis of biologically important indole scaffolds is achieved.

A mild and straightforward Rh(III)-catalysed macrocylization strategy is developed to deliver quinoline braced cyclophane type macrocycles based on migratory insertion of metal–carbenes into the C8-methyl group of quinoline scaffolds.

Iron-catalyzed C–H methylation with organoaluminum reagents accesses reactive cyclometalated iron(II) intermediates.

A new protocol is developed for the mono- and bis-ortho-C–H alkynylation of easily accessible benzamide derivatives using alkynyl bromides at room temperature by merging cobalt and photocatalysts.

The Ir-catalyzed enantioselective addition of an N-methyl C–H bond of 2-(methylamino)pyridine derivatives to α-trifluoromethylstyrenes proceeded via C–H activation to give chiral γ-branched amines having a trifluoromethyl-substituted stereocenter.

Pd-catalyzed aerobic C–H alkenylations at the unhindered positions of N-alkylpyrroles and 3-substituted thiophenes are developed using a pyrazolonaphthyridine ligand.

A regioselective C8 linear olefination of isoquinoline-1H-2-one with terminal (aromatic and aliphatic) alkynes is reported under Co(III) catalysis.

It was found for the first time that transient directing group controlled regiodivergent CDC reactions at both sp² and sp³ hybridized carbons of aromatic compounds with palladium catalyst.

A new glycosylation method promoted by visible light with 3,5-dimethoxyphenyl glycoside as the donor was developed.

An organo-photocatalyst catalyzed allylation of aryl ketones and aldehydes using readily available unactivated allylic substrates has been reported.

A soluble iron(II)-phthalocyanine, [Fe^II(^tBu₄Pc)(py)₂], is an effective catalyst in intramolecular C(sp³)–H bond amination of alkyl azides to give the amination products in moderate to excellent yields with a broad substrate scope.

The enantioselective first total syntheses of marine pentacyclic indolosesquiterpenoids xiamycins D (4) and E (5) have been described for the first time to the best of our knowledge.

A (4+2) annulation under Ru(II)-catalysis is reported using aromatic hydroxamic acid esters as the oxidizing directing group and allylic amides as unactivated olefin coupling partners, delivering a wide variety of aminomethyl isoquinolinones in good to excellent yields.

An atroposelective Fujiwara–Moritani reaction towards the synthesis of alkenylthioglycoside is reported. β-thioglucose moiety is used both as a directing group for the C–H bond activation and as a chiral source inducing axial chirality.

Three-dimensionally propagated imidazolium-containing mesoporous coordination polymer and organic polymer platforms were assembled to develop the demanding single-site heterogeneous ‘Pd(II)–NHC’-based oxidative C–H functionalization catalysts.

A diverse functionalization and synthesis of heterocycles using K₂S₂O₈ as oxidant and glucose as persulfate activator in water at room temperature is reported.

A rhodium-catalysed direct formylmethylation adopting vinylene carbonate as an ethynol equivalent is reported.

A visible light-mediated photocatalyzed C–C-bond benzylic functionalization of phenolic ether-containing drug-like compounds is presented.

A straightforward methodology for the selective synthesis of high-value added Z-2,2,2-trifluoroethylated acrylamides by Pd-catalyzed C–H bond activation at room temperature.

A site-selective direct arylation reaction of carbazole and other N-heterocycles with diazo-naphthalen-2(1H)-ones has been developed.

Pd(II)-Catalyzed highly enantioselective arylation of unbiased methylene C(sp³)–H bonds using easily accessible 3,3′-F₂-BINOL as a ligand was reported.