Expedient synthesis of N-acyl anthranilamides and β-enamine amides by the Rh(III)-catalyzed amidation of aryl and vinyl C-H bonds with isocyanates

Manganese(I)-Catalyzed Direct Addition of C(sp3)-H Bonds to Aryl Isocyanates

The addition of C-H bonds to isocyanates catalyzed by transition metals is a highly auspicious methodology for providing synthetically and biologically important amides. However, the substrates are limited to C(sp2)-H bonds. In this work, an efficient manganese(I)-catalyzed direct addition reaction of C(sp3)-H bonds of 8-methylquinolines to aryl isocyanates has been developed, leading to the synthesis of various α-quinolinyl amide compounds in moderate to high yields. The reaction has a broad range of substrates and a good functional group tolerance. A possible mechanism is proposed based on the experimental results.

Selenated NHC-Pd(II) Pincer Complex Catalyzed, Temperature-Dependent Selective Hydroamination and Oxidative Amination of Olefins: Formation of Enamine Esters and β-Amino Esters under Solvent-Free and Aerobic Conditions

NHC-Pd(II) pincer catalyzed oxidative amination and hydroamination of olefins is developed under solvent-free aerobic conditions. Reaction offered a temperature-controlled synthesis of (Z)-enamine and β-amino esters to provide easy access and remarkable functional group tolerance for a variety of enamines. The developed approach renders an opportunity of scalability and flexibility, and besides this, the produced enamines can be transformed into many N-containing heterocycles, underscoring its potential usage in synthetic and pharmaceutical chemistry. Moreover, it is the first report for coupling of aniline with styrene.

Synthesis of Tetrasubstituted Enamines through Borane-Catalyzed Hydrogenations

This paper describes a B(C6F5)3-catalyzed hydrogenation of β-substituted α,β-unsaturated imines by using as low as 0.2 mol % catalyst. A variety of tetrasubstituted enamines were afforded in 95-99% yields. It provides an efficient and facile way without the need for column chromatography purification.

Synthesis of Spiroisoindolinones via Ru(II)-Catalyzed Spiroannulation of N-Acyl Ketimines with Aryl Isocyanates/Isothiocyanates through Aromatic C-H Bond Activation

Herein, we disclose the first report on Ru(II)-catalyzed amidation/thioamidation of 3-hydroxy-3-arylisoindolinones with isocyanates/isothiocyanates, respectively. The reaction furnishes spiroisoindolinones via sequential C-H functionalization of ortho C-H bond followed by intramolecular cyclization in moderate to high yields (up to 94%). Moreover, the developed strategy is highly atom-economical and site-selective and shows diverse substrate generality. Also, synthesized spiroisoindolinones undergo several chemical transformations.

Access to Amides and Lactams via Pyridotriazole as a Transformable Directing Group

Amide and lactam frameworks were synthesized via an efficient two-step strategy. In this protocol, pyridotriazoles were first treated with isocyanates to form the corresponding amides, which were found to be sufficiently reactive to undergo subsequent intramolecular N-H insertion in the absence of any additional reagents or catalysts.

Ruthenium-Catalyzed Aminocarbonylation with Isocyanates Through Weak Coordinating Groups

Introducing amide functional groups under mild conditions has growing importance owing to the prevalence of such moiety in biologically active molecules. Herein, we disclose a mild protocol for the directed ruthenium-catalyzed C-H aminocarbonylation with isocyanates as the amidating agents developed through high-throughput experimentation (HTE). The redox-neutral and base-free reaction is guided by weakly Lewis basic functional groups, including anilides, lactams and carbamates to access anthranilamide derivatives. The synthetic utility of this transformation is reflected by large-scale synthesis and late-stage functionalization.

Ru3 (CO)12 -Catalyzed Modular Assembly of Hemilabile Ligands by C-H Activation of Phosphines with Isocyanates

Hemilabile ligands have been applied extensively in transition metal catalysis, but preparations of these molecules typically require multistep synthesis. Here, modular assembly of diverse phosphine-amide ligands, including related axially chiral compounds, is first reported through ruthenium-catalyzed C-H activation of phosphines with isocyanate directed by phosphorus(III) atoms. High reactivity and regioselectivity can be obtained by using a Ru₃ (CO)₁₂ catalyst with a mono-N-protected amino acid ligand. This transformation significantly expands the pool of phosphine-amide ligands, some of which have shown excellent efficiency for asymmetric catalysis. More broadly, the discovery constitutes a proof of principle for facile construction of hemilabile ligands directly from the parent monodentate phosphines by C-H activation with ideal atom, step and redox economy. Several dinuclear ruthenium complexes were characterized by single-crystal X-ray diffraction analysis revealing the key mechanistic features of this transformation.

Manganese-catalyzed hydroarylation of multiple bonds

Transition metal-catalyzed C-H activation has become a promising strategy in organic synthesis due to its improved atom-, step- and resource economy. Considering the Earth's abundance, economic benefits, and low toxicity, 3d metal catalysts for C-H activation have received a significant focus. In particular, organometallic manganese-catalyzed C-H activation has proven to be versatile and suitable for a wide range of transformations such as C-H addition to π-components, arylation, alkylation, alkynylation, amination, and many more. Among them, manganese-catalyzed C-H addition to C-C and C-heteroatom multiple bonds exhibited unique and promising reactivity to construct a wide range of complex organic molecules. In this review, we highlight the developments in the field of manganese-catalyzed hydroarylation of multiple bonds via C-H activation with a range of applications until August 2022.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Different Lewis Acid Promotor-Steered Highly Regioselective Phosphorylation of Tertiary Enamides

Different Lewis acid promotor-steered highly regioselective phosphorylation of tertiary enamides with diverse H-phosphonates or H-phosphine oxides was developed. Under the catalysis of iron salt, the phosphonyl group was introduced into the α-position of tertiary enamides, affording various α-phosphorylated amides in high efficiency. On the other hand, the β-phosphorylated tertiary enamides were efficiently obtained as the products in the presence of manganese(III) acetylacetonate.

Manganese(III)-promoted highly stereoselective phosphorylation of acyclic tertiary enamides to synthesize E-selective β-phosphoryl enamides

A concise manganese(III)-promoted stereoselective β-phosphorylation of acyclic tertiary enamides and diverse H-phosphine oxides was achieved. This reaction proceeds with absolute E-selectivity in contrast to Z-selectivity obtained in other previous works and affords various E-selective β-phosphorylated tertiary enamides in high efficiency. To the best of our knowledge, this is the first case of E-selective β-phosphorylation of tertiary enamides through C-H functionalization. In addition, the method features broad substrate scope, good functional group compatibility and efficient scale-up.

RhodiumIII-catalyzed remote difunctionalization of arenes assisted by a relay directing group

Rhodium-catalyzed diverse tandem twofold C-H bond activation reactions of para-olefin-tethered arenes have been realized, with unsaturated reagents such as internal alkynes, dioxazolones, and isocyanates being the coupling partner as well as a relay directing group which triggers cyclization of the para-olefin group under oxidative or redox-neutral conditions. The reaction proceeded via initial ortho-C-H activation assisted by a built-in directing group in the arene, and the ortho-incorporation of the unsaturated coupling partner simultaneously generated a relay directing group that allows sequential C-H activation at the meta-position and subsequent cyclization of the para-olefins. The overall reaction represents C-C or N-C difunctionalization of the arene with the generation of diverse 2,3-dihydrobenzofuran platforms. The catalytic system proceeded with good efficiency, simple reaction conditions, and broad substrate scope. The diverse transformations of the products demonstrated the synthetic utility of this tandem reaction.

Rh-Catalyzed Highly Enantioselective Hydrogenation of Functionalized Olefins with Chiral Ferrocenylphosphine-Spiro Phosphonamidite Ligands

A highly efficient Rh-catalyzed hydrogenation of functionalized olefins has been realized by a new family of highly rigid chiral ferrocenylphosphine-spiro phosphonamidite ligands. Excellent enantiocontrol (>99% ee in most cases) was achieved with a wide range of α-dehydroamino acid esters and α-enamides. This practicable catalytic system was further applied in the scalable synthesis of highly optically pure key intermediates of cinacalcet and d-phenylalanine.

Rapid Access to Multisubstituted Acrylamides from Cyclic Ketones via Palladium/Norbornene Cooperative Catalysis

A strategy to access diverse multisubstituted acrylamides from cyclic ketones is realized via palladium/norbornene-catalyzed α-carbamoylation and ipso-functionalization of the corresponding enol triflates. The development of bulky C2 secondary amide-substituted norbornene cocatalysts is the key to achieve the desired reactivity and selectivity. Readily available carbamoyl chlorides serve as effective electrophiles; various moieties including alkenyl, hydrogen, alkynyl, aryl, and alkyl groups can be installed at the ipso position. In addition, tandem α-carbamoylation/ipso-annulations are demonstrated to furnish lactam-containing polycyclic scaffolds. The utility of this method is exemplified in the streamlined preparation of a platelet-activating factor (PAF)-antagonist.

Cp*Co(III)-catalyzed thiocarbamate directed C−H aminocarbonyl-ation, amination, and cascade annulation of pyrroles

Cobalt(III)-catalyzed thiocarbamate directed aminocarbonylation and amination of C−H bond are described to access diverse amides. Biologically relevant pyrrolo[1,2-c]imidazoles were readily accessed via one-pot intramolecular cyclization at thiocarbamoyl directing group. Notably,...

Multi-component cascade reaction of 3-formylchromones: highly selective synthesis of 4,5-dihydro-[4,5'-bipyrimidin]-6(1H)-one derivatives

A novel protocol for the construction of highly functionalized bipyrimidine derivatives 4 and 5 from 3-formyl-chromones, ethyl 2-(pyridine-2-yl)acetate derivatives, and amidine hydrochlorides via an interesting and considerably complex multi-component cascade reaction was developed. The cascade reaction was manifested by refluxing a mixture of the three substrates in acetonitrile or DMF along with Cs2CO3. A series of 4,5-dihydro-[4,5'-bipyrimidin]-6(1H)-ones (DBPMOs) 4 was constructed regioselectively in suitable to excellent yields. Moreover, intermediates 4 then underwent a novel, metal- and oxidant-free cascade reaction to produce a series of [4,5'-bipyrimidin]-6(1H)-ones (BPMOs) 5. The formation of the bipyrimidine derivatives 4-5 was enabled by the formation of five bonds and the cleavage of one bond in one pot. This protocol can be used in the synthesis of functionalized bipyrimidine derivatives via a multi-component one-pot cascade reaction rather than multi-step reactions, which is suitable for both combinatorial and parallel syntheses of bipyrimidine derivatives.

Palladium-catalyzed Ugi-type reaction of 2-iodoanilines with isocyanides and carboxylic acids affording N-acyl anthranilamides

The first palladium-catalyzed Ugi-type multicomponent reaction for the synthesis of N-acyl anthranilamides from isocyanides, 2-iodoanilines and carboxylic acids has been developed. This method provides expeditious and highly efficient access to structurally diverse N-acyl anthranilamides from readily available starting materials with good functional group compatibility. The utility of this method has been demonstrated by the late stage functionalization of two commercial drugs: Flurbiprofen and Loxoprofen.

K2S2O8-mediated regio- and stereo-selective thiocyanation of enamides with NH4SCN

A direct and straightforward thiocyanation of enamides with NH₄SCN under metal-free conditions has been accomplished. A variety of (E)-β-thiocyanoenamides are readily produced in a regio- and stereo-selective manner. The protocol features mild reaction conditions, good functional group tolerance and operational simplicity. The potential utility of this strategy was further demonstrated by transformation of thiocyanate into thiotetrazole-containing compounds and a Pd-catalyzed cross-coupling reaction to afford six- or seven-membered sulfur-containing heterocycles. Mechanistic insights into the reaction indicate that the reaction may proceed via a radical mechanism.

Rhodium(iii)-catalyzed annulation of enamides with sulfoxonium ylides toward isoquinolines

An efficient rhodium(iii)-catalyzed C-H activation followed by intermolecular annulation between enamides and sulfoxonium ylides has been developed. The transformation proceeds smoothly with a broad range of substrates, affording a series of isoquinoline derivatives in moderate to good yields under additive-free conditions.

Photocatalytic decarboxylative alkylation of silyl enol ether and enamide with N-(acyloxy)phthalimide using ammonium iodide

Under visible light, a catalytic amount of ammonium iodide promotes the decarboxylative alkylation of silyl enol ether and enamide with aliphatic N-(acyloxy)phthalimide through the photoactivation of a transiently assembled chromophore.

Photoinitiated stereoselective direct C(sp2)–H perfluoroalkylation and difluoroacetylation of enamides

Photoinitiated regio- and stereoselective C(sp²)–H perfluoroalkylation and difluoroacetylation of enamides are developed, furnishing biologically and physiologically privileged fluoro-containing enamide scaffolds.

Recent advances in chelation-assisted site- and stereoselective alkenyl C–H functionalization

This review highlights recent advances in vicinal- and geminal-group-directed alkenyl C–H functionalizations which proceeded by endo- and exo-cyclometallation.

Visible-Light-Induced Regio- and Stereoselective C(sp2)-H Trifluoroethylation of Enamides with 2,2,2-Trifluoroethyl Iodide

A photoredox-catalyzed regio- and stereoselective trifluoroethylation reaction of enamides using commercially available 2,2,2-trifluoroethyl iodide as trifluoroethylating agents has been developed, furnishing geometrically defined and synthetically and physiochemically pivotal β-trifluoroethylated enamides bearing a diverse range of functional groups.

Direct C-H bond halogenation and pseudohalogenation of hydrocarbons mediated by high-valent 3d metal-oxo species

Late-stage direct functionalization of the C-H bond is synthetically desirable. Metalloenzymes having metal-oxo active sites are well known to selectively catalyze hydroxylation and halogenation reactions with high efficiency. This review highlights the recent developments in the field of direct C-H halogenation and pseudohalogenation reactions catalyzed by the functional models of metalloenzymes.

Analysis of Benzenoid Substitution Patterns in Small Molecule Active Pharmaceutical Ingredients

Previous analyses have revealed that benzenoid rings are prevalent scaffolds in active pharmaceutical ingredients (APIs). Here, we analyze the substitution patterns of benzenoid rings in small molecule APIs approved by the FDA through 2019 and show that only a few substitution patterns (1-, 1,2-, 1,4-, and 1,2,4-) prevail, and the distribution has remained relatively constant over time. We postulate the connection between available synthetic methods and the occurrence of a few benzenoid substitution patterns by providing an overview of synthetic methods that elaborate existing substitution patterns and those that create new substitution patterns, including those of the former that are favored by medicinal chemists. Finally, we calculated medicinal chemistry properties of benzenoid containing APIs that are often used by practitioners as design elements, including "druglikeness", shape, complexity, and similarity/diversity and discuss these properties in the context of synthesis.

Identification of the Side Products That Diminish the Yields of the Monoamidated Product in Metal-Catalyzed C-H Amidation of 2-Phenylpyridine with Arylisocyanates

The Ru(II)-catalyzed amidation of 2-arylpyridines with aryl isocyanates via C-H bond activation is less efficient than described previously, due to the formation of a series of side products, which were readily identified using direct infusion electrospray mass spectrometry and high-performance liquid chromatography-mass spectrometry.

Nickel-catalyzed reductive amidation of aryl-triazine ethers

The reaction of activated phenolic compounds, 2,4,6-triaryloxy-1,3,5-triazine (aryl-triazine ethers), with various isocyanates or carbodiimides in the presence of a nickel pre-catalyst resulted in the synthesis of aryl amides in good to excellent yields.

Cobalt(III)-Catalyzed C-H Amidation of Dehydroalanine for the Site-Selective Structural Diversification of Thiostrepton

Thiostrepton is a potent antibiotic against a broad range of Gram-positive bacteria, but its medical applications have been limited by its poor aqueous solubility. In this work, the first C(sp2 )-H amidation of dehydroalanine (Dha) residues was applied to the site selective modification of thiostrepton to prepare a variety of derivatives. Unlike all prior methods for the modification of thiostrepton, the alkene framework of the Dha residue is preserved and with complete selectivity for the Z-stereoisomer. Additionally, an aldehyde group was introduced by C-H amidation, enabling oxime ligation for the installation of an even greater range of functionality. The thiostrepton derivatives generally maintain antimicrobial activity, and importantly, eight of the derivatives displayed improved aqueous solubility (up to 28-fold), thereby addressing a key shortcoming of this antibiotic. The exceptional functional group compatibility and site selectivity of CoIII -catalyzed C(sp2 )-H Dha amidation suggests that this approach could be generalized to other natural products and biopolymers containing Dha residues.

Merging alkenyl C–H activation with the ring-opening of 1,2-oxazetidines: ruthenium-catalyzed aminomethylation of enamides

1,2-Oxazetidines have been utilized as formaldimine precursors for the direct aminomethylation of enamides under a Ru(ii) species.

Recent advances in the direct β-C(sp2)–H functionalization of enamides

Recent advances in the direct β-C(sp²)–H functionalization of enamides, mainly including arylation, alkenylation, alkynylation, alkylation, acylation, sulfonylation, phosphorylation, and others, are reported.

Palladium-catalyzed decarboxylative ortho-amidation of O-methyl ketoximes with oxamic acids

The first palladium-catalyzed ortho-amidation of ketoximes has been developed with readily available, easy to handle and environment-friendly N,N-disubstituted oxamic acids as the amidation sources. When N-monosubstituted oxamic acids are used as the substrates, the formed ortho-amidated ketoximes undergo further intramolecular cyclization to provide 3-methyleneisoindolinones.

Photoredox-catalyzed stereoselective alkylation of enamides with N-hydroxyphthalimide esters via decarboxylative cross-coupling reactions

Stereoselective β-C(sp2)-H alkylation of enamides with redox-active N-hydroxyphthalimide esters via a photoredox-catalyzed decarboxylative cross-coupling reaction is demonstrated. This methodology features operational simplicity, broad substrate scopes, and excellent stereoselectivities and functional group tolerance, affording a diverse array of geometrically defined and synthetically valuable enamides bearing primary, secondary or tertiary alkyl groups in satisfactory yields.

The ruthenium-catalyzed C-H functionalization of enamides with isocyanates: easy entry to pyrimidin-4-ones

Ruthenium-catalyzed heteroannulation between enamides and isocyanates has been realized as a complementary approach to conventional strategies for the synthesis of pyrimidin-4-ones. High step- and atom-economy was achieved for the rapid construction of such privileged scaffolds, which are found in a multitude of pharmaceutical compounds. The generality and practicability of this transformation were reflected by the broad scope of substrates with diverse functional groups, large-scale synthesis, and late-stage diversification.