Rhodium-Catalyzed CH Alkynylation of Arenes at Room Temperature

Gold(i)-catalyzed Nicholas reaction with aromatic molecules utilizing a bifunctional propargyl dicobalt hexacarbonyl complex

A benchtop-stable reagent for the catalytic Nicholas reaction with aromatic molecules was developed.

Palladium-catalyzed regioselective C–H alkynylation of indoles with haloalkynes: access to functionalized 7-alkynylindoles

A palladium-catalyzed exclusively selective alkynylation of indoles has been reported, affording concise access to 7-alkynylindoles from readily available starting materials.

Cross-dehydrogenative alkynylation of sulfonamides and amides with terminal alkynes via Ir(iii) catalysis

Primary sulfonamides are widely used structural skeletons in bioactive molecules, however their direct modification via C–H functionalization remains to be developed.

Room-temperature Pd(ii)-catalyzed direct C–H TIPS-ethynylation of phenylacetic amides with terminal alkynes

Ligand-promoted Pd(ii)-catalyzed direct C–H alkynylation of phenylacetic amides has been developed, where 8-aminoquinoline was employed as a removable bidentate auxiliary, giving rise to optically pure ortho-alkynylated α-APA.

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.

European Restrictions on 1,2-Dichloroethane: C-H Activation Research and Development Should Be Liberated and not Limited

Plan B: 1,2-Dichloroethane was recently subject to regulatory controls in the European Union that will severely limit its commercial use. The practitioners of innovative synthetic methods, particularly C-H bond activation, need to investigate alternative solvents if their chemistry is to stay relevant.

Rhodium(III)-Catalyzed C-H Alkynylation of N-Methylsulfoximines

A rhodium(III)-catalyzed direct C-H alkynylation of a wide range of N-methylsulfoximines with (bromoethynyl)triisopropylsilane has been developed. This protocol is compatible with both (S,S)-diaryl sulfoximines and (S,S)-alkyl aryl sulfoximines, and shows mild conditions, and good functional group tolerance. The synthetic utility of this method has been demonstrated by subsequent various transformations of the products.

Regioselective Formal [4 + 2] Cycloadditions of Enaminones with Diazocarbonyls through RhIII-Catalyzed C-H Bond Functionalization

A regioselective formal [4 + 2] cycloaddition for the assembly of highly functionalized benzene rings was successfully developed. In this reaction, olefinic C-H bond functionalization/cyclization cascade reaction followed by rearomatization led to the desired molecules in one step under mild reaction conditions. This protocol also displays a broad substrate scope and good tolerance to a wide range of functional groups. Additionally, the potential utility for the synthesis of highly conjugated polybenzenes and diversification of natural products was also demonstrated.

Investigations of alkynylbenziodoxole derivatives for radical alkynylations in photoredox catalysis

The alkynylbenziodoxole derivatives are recently developed alkynylation reagents in organic synthesis, which demonstrate excellent radical alkynylation reactivity in photoredox catalysis reactions. Herein we report the synthesis of alkynylbenziodoxole derivatives with difluoro, monofluoro, monomethoxy, and dimethoxy substitution on the benziodoxole moiety, and investigated their radical alkynylation reactivity for the first time. A series of mechanistic experiments were conducted to study the radical acceptor and oxidative quencher reactivity of alkynylbenziodoxoles, in which unsubstituted alkynylbenziodoxoles played balancing roles in both processes, while electron-rich benziodoxole derivatives demonstrate synthetic advantages in some cases.

Cu-Catalyzed Oxyalkynylation and Aminoalkynylation of Unactivated Alkenes: Synthesis of Alkynyl-Featured Isoxazolines and Cyclic Nitrones

A convenient and efficient vicinal oxyalkynylation/aminoalkynylation of internal unactivated alkenes is achieved by means of a Cu-catalyzed radical cascade reaction of unsaturated ketoximes with ethynylbenziodoxolone (EBX) reagents. This protocol enables the synthesis of structurally valuable isoxazolines or cyclic nitrones and the introduction of an important alkyne group in a single operation. The reaction is characterized by a broad substrate scope for both unsaturated ketoximes and alkynylation reagents and a low catalyst loading.

Direct ortho-Selective C-H Functionalization of Carboxybenzyl-Protected Arylalkylamines via Ir(III)-Catalyzed C-H Activation

A convenient and practical approach to synthesize ortho-alkynylated arylalkylamines through ortho-selective C-H functionalization has been developed using Cbz-amide as the directing group and Ir(III) as the catalyst. Various substrates were well tolerated, affording the corresponding products in moderate to good yields. Moreover, preliminary mechanistic study revealed the role of the amide as the coordination center to cooperate with the Ir(III) complex during C-H activation. Development of this Cbz-amide-promoted C_Ar-H functionalization offers a practical approach with potential applications in organic synthesis.

Broad-Scope Rh-Catalyzed Inverse-Sonogashira Reaction Directed by Weakly Coordinating Groups

We report the alkynylation of C(sp2)-H bonds with bromoalkynes (inverse-Sonogashira reaction) directed by synthetically useful ester, ketone, and ether groups under rhodium catalysis. Other less common directing groups such as amine, thioether, sulfoxide, sulfone, phenol ester, and carbamate are also suitable directing groups. Mechanistic studies indicate that the reaction proceeds by a turnover-limiting C-H activation step via an electrophilic-type substitution.

N-Heterocyclic carbene palladium-catalyzed cascade annulation/alkynylation of 2-alkynylanilines with terminal alkynes

A straightforward and highly effective N-heterocyclic carbene-palladium catalyzed cascade annulation/alkynylation of 2-alkynylanilines with terminal alkynes has been enabled to afford free (NH)-3-alkynylindole derivatives in moderate to good yields. This protocol features mild conditions, broad substrate scope, and high atom- and step-economy. Notably, the resultant 3-alkynylindoles could be conveniently transformed into a variety of functionalized indole scaffolds, thus illustrating their potential applications in synthetic and pharmaceutical chemistry.

Pd(ii)-Catalyzed gamma-C(sp3)–H alkynylation of amides: selective functionalization of R chains of amides R1C(O)NHR

The first example of palladium(ii)-catalyzed alkynylation of an unactivated gamma C(sp³)–H bond of alkyl amides (cyclic, linear, and amino acids) is reported.

C–H bond cleavage occurring on a Rh(v) intermediate: a theoretical study of Rh-catalyzed arene azidation

Our theoretical calculations indicated that the oxidation of Rh(iii) to Rh(v) by PhI(OAc)OTs is a facile process. Subsequent electrophilic deprotonation was shown to occur from a Rh(v) intermediate rather than a Rh(iii) intermediate.

Palladium-catalyzed primary amine-directed regioselective mono- and di-alkynylation of biaryl-2-amines

Palladium-catalyzed primary amine-directed controlled alkynylation of biaryl-2-amines has been developed by using haloalkynes as an alkynylating reagent.

A versatile rhodium(iii) catalyst for direct acyloxylation of aryl and alkenyl C–H bonds with carboxylic acids

Rh(iii)-Catalyzed highly regioselective direct acyloxylation of aryl and alkenyl sp² C–H bonds with various carboxylic acids has been developed.

Rh(iii)-Catalyzedortho-C–H alkynylation ofN-phenoxyacetamides with hypervalent iodine-alkyne reagents at room temperature

Directing group ONHR preservedortho-alkynylation under mild conditions catalyzed by rhodium is reported.

Copper-catalyzed aminoalkynylation of alkenes with hypervalent iodine reagents

A copper-catalyzed aminoalkynylation of alkenes is achieved with ethynylbenziodoxolone (EBX) reagents under mild conditions with only 1 mol% copper catalyst. This transformation allows for rapid construction of diverse important azahetereocycles and installation of valuable alkyne groups in one step. The developed method features remarkable substrate scope for both terminal and internal alkenes as well as different alkynyl groups, presenting great potential for broad applications in synthesis, bioconjugation, and molecular imaging.

Ruthenium-Catalyzed Peri- and Ortho-Alkynylation with Bromoalkynes via Insertion and Elimination

The alkynylation of naphthols takes place with total regiocontrol at the peri position of the hydroxyl group in the presence of [RuCl₂(p-cymene)]₂ as the catalyst. This reaction features high functional group tolerance. The related ortho-alkynylation of benzoic acids proceeds under similar conditions and also shows wide functional group tolerance. Both reactions proceed through metalation, insertion of the alkyne, and bromide elimination.

NH2-Directed C-H Alkenylation of 2-Vinylanilines with Vinylbenziodoxolones

The first directing-group-mediated C-H alkenylation with alkenyl-λ³-iodanes as electrophilic alkene-transfer reagents has been developed. The application of free aromatic amines as challenging but synthetically valuable directing groups in combination with an Ir^III catalyst enabled the synthesis of highly desirable 1,3-dienes in excellent yields of up to 98% with high to perfect (Z,E) stereoselectivity. A broad substrate scope and further synthetic modifications are demonstrated.

Indole- and Pyrrole-BX: Bench-Stable Hypervalent Iodine Reagents for Heterocycle Umpolung

The one-step synthesis of the bench-stable hypervalent iodine reagents IndoleBX and PyrroleBX using mild Lewis acid catalyzed conditions is reported. The new reagents are stable up to 150 °C and were applied in the C-H arylation of unactivated arenes using either rhodium or ruthenium catalysts. A broad range of heterocyclic systems of high interest for synthetic and medicinal chemistry was accessed in high yields. The developed C-H functionalization could not be achieved using reported reagents or methods, highlighting the unique reactivity of Indole- and Pyrrole-BX.