Ir(III)-Catalyzed Direct C–H Functionalization of Arylphosphine Oxides: A Strategy for MOP-Type Ligands Synthesis

Pd/Chiral Phosphoric Acid-Enabled Asymmetric Intramolecular Double C-H Activation Reaction for the Synthesis of P-Stereogenic Benzophosphole Oxides

A Pd-catalyzed intramolecular asymmetric double C-H activation reaction was reported, and a BINOL skeleton-based chiral phosphoric acid (CPA) was identified as a suitable ligand for this transformation. A broad range of P-stereogenic benzophosphole oxides were synthesized in moderate to excellent yield with high levels of enantioselectivity (≤96% ee).

Rh(II)-catalysed N2-selective arylation of benzotriazoles and indazoles using quinoid carbenes via 1,5-H shift

An efficient Rh(II)-catalyzed highly selective N2-arylation of benzotriazole, indazole, and 1,2,3 triazole is developed using diazonaphthoquinone. The developed protocol is extended with a wide scope. In addition, late-stage arylation of these scaffolds tethered with bioactive molecules is explored. Control experiments and DFT calculations reveal that the reaction proceeds presumably via nucleophilic addition of the N2 (of the 1H tautomer) center to quinoid-carbene followed by a 1,5-H shift.

Beyond Triphenylphosphine: Advances on the Utilization of Triphenylphosphine Oxide

Triphenylphosphine oxide is a well-known industrial waste byproduct, and thousands of tons of it are generated every year. Due to its chemical stability and limited applications, settlement of this waste issue has drawn extensive attention from chemists. The reduction of triphenylphosphine oxide to triphenylphosphine is heretofore the most employed solution, and is well reviewed. In view of our recent studies on the selective and efficient conversion of Ph3P(O) to other valuable organophosphorus chemicals by using sodium, the present perspective mainly highlights the advances on the utilization of Ph3P(O) to prepare a diverse range of functional organophosphorus compounds, except Ph3P, via selective P-C, C-H, and P-O bond cleavages.

Rh(II)-Catalyzed Synthesis of N-Aryl 2-pyridone Using 2-Oxypyridine and Diazonaphthoquinone Via 1,6-Benzoyl Migratory Rearrangement

A Rh(II)-catalyzed simple and efficient synthesis of N-arylated 2-pyridone derivatives is described using 2-oxypyridine and diazonaphthoquinone as coupling partners. The reaction proceeds through the insertion of the nitrogen atom of the 2-oxypyridine derivative into quinoid carbene and subsequent 1,6-benzoyl migratory rearrangement. The reaction is broadened with sufficient scope and has the potential to offer axially chiral N-arylated 2-pyridone derivatives under suitable asymmetric conditions.

Unveiling the Three-Component Phosphonylation on Alkynylaldehydes: Toolbox toward Fluorescent Molecules

A regioselective tandem approach for annulated napthyridines/isoquinolines embedded with the phosphine oxide group under mild reaction conditions has been achieved in good to excellent yields. The designed strategy involves the triflate-induced formation of new C sp³-P and C sp²-N bond formation in one pot. This protocol was also well tolerated for the construction of densely functionalized organo-phosphorylated chromenes in good yields. Further, phosphino-derived sulfamethazine and sulfamethoxazole drugs were also successfully synthesized in good yields. The mechanistic studies revealed that the ionic pathway and the formation of regioselective 6-endo dig cyclized products were confirmed through X-ray crystallographic studies. Interestingly, photophysical studies of selectivity selected compounds revealed their stimulating fluorescence properties.

Synthesis of N-Arylindoles from 2-Alkenylanilines and Diazonaphthalen-2(1H)-ones through Simultaneous Indole Construction and Aryl Introduction

In this paper, an efficient synthesis of N-arylindoles through the cascade reaction of 2-alkenylanilines with diazonaphthalen-2(1H)-ones is presented. Mechanistically, this reaction involves the generation of a Ru-carbene complex from diazonaphthalen-2(1H)-one, followed by carbene N-H bond insertion with 2-alkenylaniline, intramolecular cyclization, and oxidative aromatization. In this reaction, the Ru(II) complex acts as a multifunctional catalyst to promote not only the carbene formation but also the intramolecular cyclization and the dehydrogenative aromatization. Meanwhile, air acts as a green and cost-effective oxidant. To our knowledge, this is the first example in which N-arylindoles were synthesized through simultaneous introduction of the N-aryl unit and construction of the indole scaffold. Notable advantages of this method include readily accessible and halide-free substrates, additive-free reaction conditions, good efficiency, excellent atom economy, and compatibility with diverse functional groups. In addition, the utility of the product thus obtained was showcased by its diverse structural transformations.

Rhodium-catalyzed selective direct arylation of phosphines with aryl bromides

The widespread use of phosphine ligand libraries is frequently hampered by the challenges associated with their modular preparation. Here, we report a protocol that appends arenes to arylphosphines to access a series of biaryl monophosphines via rhodium-catalyzed P(III)-directed ortho C-H activation, enabling unprecedented one-fold, two-fold, and three-fold direct arylation. Our experimental and theoretical findings reveal a mechanism involving oxidative addition of aryl bromides to the Rh catalyst, further ortho C-H metalation via a four-membered cyclometalated ring. Given the ready availability of substrates, our approach opens the door to developing more general methods for the construction of phosphine ligands.

Recent advances in transition-metal-catalyzed carbene insertion to C-H bonds

C-H functionalization has been emerging as a powerful method to establish carbon-carbon and carbon-heteroatom bonds. Many efforts have been devoted to transition-metal-catalyzed direct transformations of C-H bonds. Metal carbenes generated in situ from transition-metal compounds and diazo or its equivalents are usually applied as the transient reactive intermediates to furnish a catalytic cycle for new C-C and C-X bond formation. Using this strategy compounds from unactivated simple alkanes to complex molecules can be further functionalized or transformed to multi-functionalized compounds. In this area, transition-metal-catalyzed carbene insertion to C-H bonds has been paid continuous attention. Diverse catalyst design strategies, synthetic methods, and potential applications have been developed. This critical review will summarize the advance in transition-metal-catalyzed carbene insertion to C-H bonds dated up to July 2021, by the categories of C-H bonds from aliphatic C(sp³)-H, aryl (aromatic) C(sp²)-H, heteroaryl (heteroaromatic) C(sp²)-H bonds, alkenyl C(sp²)-H, and alkynyl C(sp)-H, as well as asymmetric carbene insertion to C-H bonds, and more coverage will be given to the recent work. Due to the rapid development of the C-H functionalization area, future directions in this topic are also discussed. This review will give the authors an overview of carbene insertion chemistry in C-H functionalization with focus on the catalytic systems and synthetic applications in C-C bond formation.

Catalytic Atroposelective C7 Functionalisation of Indolines and Indoles

Axially chiral atropisomeric compounds are widely applied in asymmetric catalysis and medicinal chemistry. In particular, axially chiral indole- and indoline-based frameworks have been recognised as important heterobiaryl classes because they are the core units of bioactive natural alkaloids, chiral ligands and bioactive compounds. Among them, the synthesis of C7-substituted indole biaryls and the analogous indoline derivatives is particularly challenging, and methods for their efficient synthesis are in high demand. Transition-metal catalysis is considered one of the most efficient methods to construct atropisomers. Here, we report the enantioselective synthesis of C7-indolino- and C7-indolo biaryl atropisomers by means of C-H functionalisation catalysed by chiral RhJasCp complexes.

Ruthenium-catalyzed reaction of diazoquinones with arylamines to synthesize diarylamines

The diarylamine scaffold is common in bioactive molecules. Herein, we report a Ru(ii)-catalyzed C–N cross-coupling reaction of diazoquinones with arylamines, which provides access to a range of functionalized diarylamines in 43–97% yields.

Rh(iii)-catalyzed substrate-dependent oxidative (spiro)annulation of isoquinolones with diazonaphthoquinones: selective access to new spirocyclic and oxepine-fused polycyclic compounds

An efficient protocol for the selective synthesis of novel isoquinolone-containing spirocyclic and oxepine-fused polycyclic compounds via rhodium(iii)-catalyzed (spiro)annulation of NH-isoquinolones with diazonaphthalen-2(1H)-ones is reported.

Computational Insights into Different Regioselectivities in Ir-Porphyrin-Catalyzed C–H Insertion Reaction of Quinoid Carbene

The mechanisms and regioselectivities of Ir-porphyrin-catalyzed C–H insertion reaction of quinoid carbene (QC) were investigated with density functional theory (DFT) calculations. The competing catalytic cycles were identified as the hydrogen-atom...

Rhodium-catalyzed reaction of diazoquinones with allylboronates to synthesize allylphenols

A rhodium-catalyzed reaction of diazoquinones and allylboronates was developed, which provides access to a range of substituted allylphenols under mild conditions.

Iridium(III)-Catalyzed C(3)-H Alkylation of Isoquinolines via Metal Carbene Migratory Insertion

An Ir(III)-catalyzed C(3)-H alkylation of N-acetyl-1,2-dihydroisoquinolines with diverse acceptor-acceptor diazo compounds has been achieved under a single catalytic system via metal carbene migratory insertion. Moreover, further synthetic transformations of the alkylated products such as aromatization, selective decarboxylation, and decarbonylation lead to the formation of several synthetically viable isoquinoline derivatives having immense potentials.

DFT study on Ir-quinoid catalyzed C-H functionalization: new radical reactivity or direct carbene transfer?

DFT methods are used to probe the mechanism of a newly developed Ir-quinoid catalyzed C(sp³)-H functionalization of 1,4 dienes. The lowest energy pathway proceeds via an old-school concerted C-H insertion as opposed to a unique hydrogen atom transfer process proposed previously. The concertedness of the reaction shows an intriguing dependence on sterics of the diene leading to either inserted or dehydrogenated products. We use these new insights to tune the axial ligand, and design a more efficient catalyst.

Transition-Metal-Catalyzed C-H Bond Functionalization of Arenes/Heteroarenes via Tandem C-H Activation and Subsequent Carbene Migratory Insertion Strategy

The past decade has witnessed tremendous developments in transition-metal-catalyzed C-H bond activation and subsequent carbene migratory insertion reactions, thus assisting in the construction of diverse arene/heteroarene scaffolds. Various transition-metal catalysts serve this purpose and provide efficient pathways for an easy access to substituted heterocycles. A brief introduction to metal-carbenes has been provided along with key mechanistic pathways underlying the coupling reactions. The purpose of this review is to provide a concise knowledge about diverse directing group-assisted coupling of varied arenes/heteroarenes and acceptor-acceptor/donor-acceptor diazo compounds. The review also highlights the synthesis of various carbocycles and fused heterocycles through diazo insertion pathways, via C-C, C-N and C-O bond forming reactions. The mechanism usually involves a C-H activation process, followed by diazo insertion leading to subsequent coupling.

Construction of Bulky Ligand Libraries by Ru(II)-Catalyzed P(III)-Assisted ortho-C-H Secondary Alkylation

Modification of commercially available biaryl monophosphine ligands via ruthenium^(II)-catalyzed P^(III)-directed-catalyzed ortho C-H secondary alkylation is described. The use of highly ring-strained norbornene as a secondary alkylating reagent is the key to this transformation. A series of highly bulky ligands with a norbornyl group were obtained in excellent yields. The modified ligands with secondary alkyl group outperformed common substituted phosphines in the Suzuki-Miyaura cross-coupling reaction at a ppm mole level of Pd catalyst.

Iridium(III)-Catalyzed C−H Functionalization of Triarylphosphine Oxides with Diazo Dicarbonyl Compounds: Synthesis of α-Aryl 1,3-Dicarbonyl Derivatives

A novel (pentamethylcyclopenta-1,3-dienyl)iridium(III)-catalyzed direct C–H functionalization of triarylphosphine oxides with diazo dicarbonyl compounds through carbene insertion has been developed. This strategy provides a simple and efficient route to the construction of α-arylated 1,3-dicarbonyl compounds, which are important building blocks in pharmaceutical chemistry.

Direct Synthesis of ortho-Halogenated Arylphosphonates via a Three-Component Reaction Involving Arynes

A three-component reaction involving arynes, trialkyl phosphites, and halides has been achieved under mild reaction conditions. This transformation provides a direct synthetic approach to ortho-halogenated arylphosphonates, which could be rapidly converted to diversely ortho-functionalized arylphosphorus compounds.

Cooperative Ligand-Promoted P(III)-Directed Ruthenium-Catalyzed Remote Meta-C-H Alkylation of Tertiary Phosphines

Herein, we disclose a ruthenium-catalyzed meta-selective C-H activation of phosphines by using intrinsic P^(III) as a directing group. 2,2,6,6-Tetramethylheptane-3,5-dione acts as the ligand and exhibits an excellent performance in boosting the meta-alkylation. The protocol allows an efficient and straightforward synthesis of meta-alkylated tertiary phosphines. Several meta-alkylated phosphines were evaluated for Pd-catalyzed Suzuki coupling and found to be superior to commercially available ortho-substituted phosphines. The practicability of this methodology is further demonstrated by the synthesis of difunctionalized phosphines.

Ruthenium/acid co-catalyzed reductive α-phosphinoylation of 1,8-naphthyridines with diarylphosphine oxides

By an in situ coupling-interrupted transfer hydrogenation strategy, a direct construction of novel α-phosphinoyl 1,2,3,4-tetrahydronaphthyridines via ruthenium/acid co-catalyzed reductive α-phosphinoylation of 1,8-naphthyridines with diarylphosphine oxides is demonstrated.

Recent quinone diazide based transformations via metal–carbene formation

Recent advancements in versatile synthetic transformations using quinone diazide based metal carbenes have been summarized.

Nickel-Catalyzed [4 + 2] Annulation of Nitriles and Benzylamines by C-H/N-H Activation

Nickel-catalyzed [4 + 2] annulation of benzylamines and nitriles via C-H/N-H bond activation, providing straightforward atom-economic access to a wide variety of multisubstituted quinazolines, is reported. Mechanistic investigation revealed that the in situ formed amidines from the coupling of benzylamines and nitriles direct the nickel catalyst to activate the ortho-C-H bond of the phenyl ring of the benzylamine.

A direct synthesis method towards spirocyclic indazole derivatives via Rh(iii)-catalyzed C–H activation and spiroannulation

A rhodium(iii)-catalyzed [4 + 1] spiroannulation of N-aryl phthalazine-diones (pyridazine-diones) with diazo compounds to construct spirocyclic indazole derivatives with diverse structures is described.

An unusual reaction mode of 1-phenylpyrazolidinones toward diazonaphthalen-2(1H)-ones featuring cascade C(sp2)–H and C(sp3)–H bond cleavage

Herein, a novel synthesis of pyrazolidinone fused 1,3-benzooxazepine derivatives via a formal [4 + 3] annulation reaction of 1-phenylpyrazolidinones with diazonaphthalen-2(1H)-ones is presented.

Copper-catalyzed arylation of polycyclic aromatic hydrocarbons by the P[double bond, length as m-dash]O group

The first example of a directed and regioselective arylation of polycyclic aromatic hydrocarbons (PAHs) by using a P[double bond, length as m-dash]O directing group is reported herein. The protocol uses a cheap copper catalyst, and results in a breakthrough meta-selective C-H functionalization of arylphosphine oxide compounds. Substrates with potential fluorescence properties, for example, pyrene and fluoranthene, were successfully arylated under the system, thus achieving an efficient modification of fluorescent molecules containing the P[double bond, length as m-dash]O functional group.

Enantioselective Synthesis of Five-Membered-Ring Atropisomers with a Chiral Rh(III) Complex

Axially chiral atropisomeric compounds are widely applied in asymmetric catalysis and medicinal chemistry, and efficient methods for their synthesis are in high demand. This applies in particular to atropisomers derived from five-membered aromatic rings because their lower barrier for rotation among the biaryl axis limits their asymmetric synthesis. We report here an enantioselective C-H functionalization method using our chiral RhJasCp complex for the synthesis of the biaryl atropisomer types that can be accessed from three different five-membered-ring heterocycles.

Ir(III)-Catalyzed C-H Functionalization of Triphenylphosphine Oxide toward 3-Aryl Oxindoles

With triphenylphosphine oxide serving as both the directing group and the reagent, we have developed a Cp*Ir(III)-catalyzed direct C-H functionalization of triphenylphosphine oxide with 3-diazooxindoles to afford a range of 3-(2-(diphenylphosphoryl)phenyl)indolin-2-one derivatives in moderate to excellent yields. The title products are potentially important building blocks for organic synthesis through various chemical transformations. This protocol is simple and efficient and offers high atom economy with only N₂ as the byproduct.

Chemoselective Rearrangement Reactions of Sulfur Ylide Derived from Diazoquinones and Allyl/Propargyl Sulfides

Here, we describe three types of rearrangement reactions of sulfur ylide derived from diazoquinones and allyl/propargyl sulfides. With Rh₂(esp)₂ as the catalyst, diazoquinones react with allyl/propargyl sulfides to form a sulfur ylide, which undergoes a chemoselective tautomerization/[2,3]-sigmatropic rearrangement reaction, a Doyle-Kirmse rearrangement/Cope rearrangement cascade reaction, or a Doyle-Kirmse rearrangement/elimination reaction, depending on the substituent of the sulfides. The protocol provides alkenyl and allenyl sulfides and multisubstituted phenols with moderate and high yields.

Transition-Metal-Free C(sp2 )-C(sp2 ) Cross-Coupling of Diazo Quinones with Catechol Boronic Esters

A transition-metal-free C(sp² )-C(sp² ) bond formation reaction by the cross-coupling of diazo quinones with catechol boronic esters was developed. With this protocol, a variety of biaryls and alkenyl phenols were obtained in good to high yields under mild conditions. The reaction tolerates various functionalities and is applicable to the derivatization of pharmaceuticals and natural products. The synthetic utility of the method was demonstrated by the short synthesis of multi-substituted triphenylenes and three bioactive natural products, honokiol, moracin M, and stemofuran A. Mechanistic studies and density functional theory (DFT) calculations revealed that the reaction involves attack of the boronic ester by a singlet quinone carbene followed by a 1,2-rearrangement through a stepwise mechanism.

Ir(iii)-Catalyzed direct C–H functionalization of N-phenylacetamide with α-diazo quinones: a novel strategy for producing 2-hydroxy-2′-amino-1,2′-biaryl scaffolds

A novel strategy is reported for the construction of 2-hydroxy-2′-amino-1,1′-biaryl scaffolds via Ir(iii)-catalyzed direct C–H bond activation under mild reaction conditions.

Co(II)-Catalyzed Regioselective Pyridine C-H Coupling with Diazoacetates

A Co(II)-catalyzed pyridyl C-H bond carbenoid insertion with α-diazoacetates has been realized. This transformation features a highly regioselective C-C bond formation at the C3-position of pyridines, providing an efficient access to diverse α-aryl-α-pyridylacetates.

Ruthenium-Catalyzed Gram-Scale Preferential C-H Arylation of Tertiary Phosphine

A general protocol for site-preferential mono-C-H arylation of tertiary phosphine ligands catalyzed by a ruthenium(II) complex was devised. This protocol gives access to a series of modified Buchwald-biaryl monophosphines on a gram scale in moderate to excellent yields. A catalytic cycle is proposed derived from knowledge of the intermediates observed by ESI-MS. Importantly, these monoarylated products could be further transformed into dibenzophosphole derivatives.