Cobalt/Salicylaldehyde-Enabled C-H Alkoxylation of Benzamides with Secondary Alcohols under Solvothermal Conditions

C-O bond formation via C-H alkoxylation remains a challenge, especially coupling with a secondary alcohol, due to its low activity and sterically encumbered property. Here, we report a general and effective cobalt-catalyzed oxidative cross-coupling of benzamides with secondary alcohols via C-H alkoxylation reaction under solvothermal conditions, enabled by a salicylaldehyde/cobalt complex. The protocol features easy operation without additives, broad substrate scope, and excellent functional tolerance. The applicability is proven by the gram-scale synthesis and modification of natural products.

Transition-metal-free approach to quinolines via direct oxidative cyclocondensation reaction of N,N-dimethyl enaminones with o-aminobenzyl alcohols

A transition-metal-free method for the construction of 3-substituted or 3,4-disubstituted quinolines from readily available N,N-dimethyl enaminones and o-aminobenzyl alcohols is reported. The direct oxidative cyclocondensation reaction tolerates broad functional groups, allowing the efficient synthesis of various quinolines in moderate to excellent yields. The reaction involves a C (sp3)-O bond cleavage and a C=N bind and a C=C bond formation during the oxidative cyclization process, and the mechanism was proposed.

Salicylaldehyde-Promoted Cobalt-Catalyzed C-H/N-H Annulation of Indolyl Amides with Alkynes: Direct Synthesis of a 5-HT3 Receptor Antagonist Analogue

A cobalt-catalyzed annulation of the C(sp²)-H/N-H bond of indoloamides with alkynes assisted by 8-aminoquinoline is reported for the synthesis of six-membered indololactams. The use of salicylaldehyde as the ligand is crucial for this transformation. The protocol has a broad scope for both alkynes and indoles. Preparing an active Co complex illustrates that salicylaldehyde plays a key role in the C-H activation step. The synthetic applications are proven by the gram-scale reaction and one-step construction of the multicyclic 5-HT3 receptor antagonist.

Progress and perspectives on directing group-assisted palladium-catalysed C-H functionalisation of amino acids and peptides

Peptide modifications can unlock a variety of compounds with structural diversity and abundant biological activity. In nature, peptide modifications, such as functionalisation at the side-chain position of amino acids, are performed using post-translational modification enzymes or incorporation of unnatural amino acids. However, accessing these modifications remains a challenge for organic chemists. During the past decades, selective C-H activation/functionalisation has attracted considerable attention in synthetic organic chemistry as a pathway to peptide modification. Various directing group strategies have been discovered that assist selective C-H activation. In particular, bidentate directing groups that enable tuneable and reversible coordination are now recognised as one of the most efficient methods for the site-selective C-H activation and functionalisation of numerous families of organic compounds. Synthetic peptide chemists have harnessed bidentate directing group strategies for selective functionalisation of the β- and γ-positions of amino acids. This method has been expanded and recognised as an effective device for the late stage macrocyclisation and total synthesis of complex peptide natural products. In this review, we discuss various β-, γ-, and δ-C(sp³)-H bond functionalisation reactions of amino acids for the formation of C-X bonds with the aid of directing groups and their application in late-stage macrocyclisation and the total synthesis of complex peptide natural products.

Remote C(sp3)–H functionalization via catalytic cyclometallation: beyond five-membered ring metallacycle intermediates

Despite impressive recent momentum gained in C(sp3)–H activation, achieving high regioselectivity in molecules containing different C–H bonds with similar high energy without abusing tailored substitution remains as one of the biggest challenges.

Room-Temperature Synthesis of Isoindolone Spirosuccinimides: Merger of Visible-Light Photocatalysis and Cobalt-Catalyzed C-H Activation

A room-temperature C-H bond functionalization of benzamides has been developed by merging a photocatalyst with a cobalt catalyst for the synthesis of isoindolone spirosuccinimides. The reaction proceeds in aerobic conditions and does not require any sacrificial external oxidants such as Ag(I) or Mn(III) salts. Visible light activates the photocatalyst, and it acts as an electron-transfer reagent and helps in the fundamental organometallic steps by modulating the oxidation state of the cobalt complex. This C-H bond functionalization and spirocyclization showed wide substrate scope and good functional group tolerance. A possible reaction mechanism was proposed from the experimental outcome, showing that C-H bond activation is irreversible and not the rate-determining step.

Step-Economical C–H Activation Reactions Directed by In Situ Amidation

Owing to the inherent ability of amides to chelate transition-metal catalysts, amide-directed C–H activation reactions constitute a major tactic in directed C–H activation reactions. While the conventional procedures for these reactions usually involve prior preparation and purification of amide substrates before the C–H activation, the step economy is actually undermined by the operation of installing the directing group (DG) and related substrate purification. In this context, directed C–H activation via in situ amidation of the crude material provides a new protocol that can significantly enhance the step economy of amide-directed C–H activation. In this short review, the advances in C–H bond activation reactions mediated or initiated by in situ amidation are summarized and analyzed.

1 Introduction

2 In Situ Amidation in Aryl C–H Bond Activation

3 In Situ Amidation in Alkyl C–H Bond Activation

4 Annulation Reactions via Amidation-Mediated C–H Activation

5 Remote C–H Activation Mediated by Amidation

6 Conclusion

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.

An atom-economical and regioselective metal-free C-5 chalcogenation of 8-aminoquinolines under mild conditions

A general and simple metal-free protocol for expedient C-H functionalization leading to the regioselective generation of C-5 chalcogenated 8-aminoquinoline analogues in up to 90% yield at room temperature (25 °C) has been established. This methodology is an eco-friendly approach to the atom-economical utilization of diaryl/dialkyl chalcogenides for direct access to chalcogenated quinolines and is scalable to the gram scale without considerable decrease in the yield of the product. It represents a practical alternative to the existing metal-catalyzed functionalization of 8-aminoquinoline derivatives with broad functional group tolerance. The controlled experiments suggest that the reaction possibly proceeds through an ionic pathway at room temperature. Furthermore, the potentiality for the functionalization of free amines in chalcogenated-8-aminoquinolines provides an attractive perspective for further elaboration of the amine substituent through chemical manipulations. The applicability of the standardized method has been augmented through late-stage antimalarial drug diversification of primaquine analogues.

Pd-Catalyzed C(sp2)-H Imidoylative Annulation: A General Approach To Construct Dibenzoox(di)azepines

A general method to construct the scaffolds of dibenzooxazepine and dibenzodiazepine, through Pd-catalyzed isocyanide insertion and intramolecular C(sp²)-H activation, has been developed. This is the first example of seven-membered heterocycle formation by C-H imidoylative annulation.

Ni(ii)-catalyzed mono-selective ortho-arylation of unactivated aryl C–H bonds utilizing amino acids as a directing group

The nickel(ii)-catalyzed ortho-arylation of unactivated C–H bonds utilizing amino acids as directing groups with aryl iodides or bromides as coupling electrophiles is described.

Ruthenium-catalyzed remote C5-sulfonation of N-alkyl-8-aminoquinolines

Ruthenium-catalyzed remote C–H sulfonation of 8-aminoquinolines with single C5-selectivity.

A computational study of cobalt-catalyzed C–H iodination reactions using a bidentate directing group with molecular iodine

A computational methodology was used to collect detailed mechanistic information on the cobalt-catalyzed C–H iodination of aromatic amides with molecular iodine using an N,N′-bidentate directing group.

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.

Chemoselective direct reductive trifluoromethylation of amides: a flexible access to functionalized α-trifluoromethylamines

A one-pot method is reported for the direct transformation of secondary amides to α-trifluoromethylamines.

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 β-arylated alkylamides via Pd-catalyzed one-pot installation of a directing group and C(sp(3))-H arylation

The synthesis of β-arylated alkylamides via alkyl C-H bond arylation has been realized by means of direct one-pot reactions of acyl chlorides, aryl iodides and 8-aminoquinoline. Depending on the structure of the starting materials, both single and double β-arylated alkylamides could be accessed.