Reusable directing groups [8-aminoquinoline, picolinamide, sulfoximine] in C(sp3)–H bond activation: present and future

Recent advances in intramolecular C–O/C–N/C–S bond formationviaC–H functionalization

This review presents the construction of C–X bonds (X = O/N/S) by using intramolecular C–H functionalization for the synthesis of heterocyclic compounds.

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.

A Two-Step Procedure for the Overall Transamidation of 8-Aminoquinoline Amides Proceeding via the Intermediate N-Acyl-Boc-Carbamates

Herein a two-step strategy for achieving overall transamidation of 8-aminoquinoline amides has been explored. In this protocol, the 8-aminoquinoline amides were first treated with Boc₂O and DMAP to form the corresponding N-acyl-Boc-carbamates, which were found to be sufficiently reactive to undergo subsequent aminolysis with different amines in the absence of any additional reagents or catalysts. To demonstrate the utility of this approach, it was applied on a number of 8-aminoquinoline amides from the recent C-H functionalization literature, enabling access to a range of elaborate amide derivatives in good to high yields.

Nickel-catalyzed direct C-H trifluoroethylation of heteroarenes with trifluoroethyl iodide

A highly selective nickel-catalyzed C-H trifluoroethylation of heteroarenes was developed with the assistance of a monodentate directing group. This protocol provides efficient access to various trifluoroethyl-substituted heteroarenes, including indoles, pyrroles, furans, and thiophenes, with commercially available CF₃CH₂I as an alkylation reagent. This robust catalytic procedure is scalable and tolerates a broad range of functional groups. Moreover, multifluoroalkylation of indoles is also viable.

Cobalt(ii)-catalyzed chelation-assisted C–H iodination of aromatic amides with I2

An air stable and inexpensive cobalt-metal, mild and efficient catalytic system.

Synthesis of unnatural α-amino acid derivatives via selective o-C–H functionalization

Selective o-C–H functionalization of aryl based amino acids including arylation, alkylation, alkynylation, halogenation, alkoxylation, and acyloxylation were developed.

Nickel-catalyzed C-H/N-H annulation of aromatic amides with alkynes in the absence of a specific chelation system

The Ni-catalyzed reaction of aromatic amides with alkynes in the presence of KOBu t involves C-H/N-H oxidative annulation to give 1(2H)-isoquinolinones. A key to the success of the reaction is the use of a catalytic amount of strong base, such as KOBu t . The reaction shows a high functional group compatibility. The reaction with unsymmetrical alkynes, such as 1-arylalkynes, gives the corresponding 1(2H)-isoquinolinones with a high level of regioselectivity. This discovery would lead to the development of Ni-catalyzed chelation-assisted C-H functionalization reactions without the need for a specific chelation system.

Synthesis of a Bicyclic Azetidine with In Vivo Antimalarial Activity Enabled by Stereospecific, Directed C(sp3)-H Arylation

The development of new antimalarial therapeutics is necessary to address the increasing resistance to current drugs. Bicyclic azetidines targeting Plasmodium falciparum phenylalanyl-tRNA synthetase comprise one promising new class of antimalarials, especially due to their activities against three stages of the parasite’s life cycle, but a lengthy synthetic route to these compounds may affect the feasibility of delivering new therapeutic agents within the cost constraints of antimalarial drugs. Here, we report an efficient synthesis of antimalarial compound BRD3914 (EC₅₀ = 15 nM) that hinges on a Pd-catalyzed, directed C(sp³)–H arylation of azetidines at the C3 position. This newly developed protocol exhibits a broad substrate scope and provides access to valuable, stereochemically defined building blocks. BRD3914 was evaluated in P. falciparum-infected mice, providing a cure after four oral doses.

Computational Study of Ni-Catalyzed C-H Functionalization: Factors That Control the Competition of Oxidative Addition and Radical Pathways

The mechanisms of Ni-catalyzed C-H arylation, alkylation, and sulfenylation with N,N-bidentate directing groups are investigated using density functional theory (DFT) calculations. While the C-H cleavage occurs via the concerted metalation-deprotonation (CMD) mechanism in all types of reactions, the subsequent C-C and C-X bond formation steps may occur via either oxidative addition to form a Ni(IV) intermediate or radical pathways involving Ni(III) complexes generated from homolytic dissociation of disulfides/peroxides or halide-atom transfer from alkyl halides. DFT calculations revealed that radical mechanisms are preferred in reactions with sterically hindered coupling partners with relatively low bond dissociation energies (BDE) such as dicumyl peroxide, heptafluoroisopropyl iodide and diphenyl disulfide. In contrast, these radical processes are highly disfavored when generating unstable phenyl and primary alkyl radicals. In such cases, the reaction proceeds via an oxidative addition/reductive elimination mechanism involving a Ni(IV) intermediate. These theoretical insights into the substrate-controlled mechanisms in the C-H functionalizations were employed to investigate a number of experimental phenomena including substituent effects on reactivity, chemo- and regioselectivity and the effects of oxidant in the intermolecular oxidative C-H/C-H coupling reactions.

Expeditious and Solvent-Free Nickel-Catalyzed C-H Arylation of Arenes and Indoles

An efficient solvent-free nickel-catalyzed method for C-H bond arylation of arenes and indoles has been developed, which proceeds expeditiously through chelation assistance. The reaction is highly selective for mono-arylation and tolerates sensitive and structurally diverse functionalities, such as halides, ethers, amines, indole, pyrrole and carbazole. This reaction represents the first example of a nickel-catalyzed C-H arylation by monochelate assistance and symbolizes a rare precedent in solvent-free C-H arylation. Mechanistic investigations by various controlled reactions, kinetic studies, and deuterium labeling experiments suggest that the arylation follows a single electron transfer (SET) pathway involving the turnover-limiting C-H nickelation process.

One-pot synthesis of quaternary carbon centered cyclobutanes via Pd(ii)-catalyzed cascade C(sp3)–H activations

A novel approach toward quaternary carbon centered cyclobutanes through Pd(ii)-catalyzed sequential intramolecular methylene C–H alkylation and intermolecular methine C–H bond arylation, alkenylation, alkylation, alkynylation, allylation, benzylation or alkoxylation is described.

Palladium-catalyzed sequential monoarylation/amidation of C(sp3)–H bonds: stereoselective synthesis of α-amino-β-lactams and anti-α,β-diamino acid

Stereoselective synthesis of α-amino-β-lactams via Pd-catalyzed sequential C(sp³)–H monoarylation/amidation is described.

Sulfinyl isobutyramide as an auxiliary for palladium(ii)-catalyzed C–H arylation and iodination of benzylamine derivatives

An original readily available and versatile bidentate 2-methylsulfinyl isobutyramide directing group has been developed for benzylamine derivatives.

Nickel-catalysed direct alkylation of thiophenes via double C(sp3)–H/C(sp2)–H bond cleavage: the importance of KH2PO4

A Ni-catalyzed C–H/C–H cross-dehydrogenative coupling (CDC) reaction was developed for constructing various highly functionalized alkyl (aryl)-substituted thiophenes.

C–H imidation: a distinct perspective of C–N bond formation

The direct imidation strategy proficiently constructs C–N bonds and creates the useful amine functional group in the molecular template.

Asymmetric alkylation of remote C(sp3)–H bonds by combining proton-coupled electron transfer with chiral Lewis acid catalysis

The catalytic asymmetric alkylation of the remote, unactivated δ-position of N-alkyl amides was enabled by the combination of visible-light-induced proton-coupled electron transfer, 1,5-hydrogen atom transfer, and chiral Lewis acid catalysis.

Iridium-catalyzed direct C–H amidation of anilines with sulfonyl azides: easy access to 1,2-diaminobenzenes

The Ir(iii)-catalyzed C–H amidation of anilines with azides is achieved, and the 2-pyrimidyl and sulfonyl moieties could be removed, offeringortho-diaminobenzenes.