Synthesis of 1(2H)-Isoquinolones by the Nickel-Catalyzed Denitrogenative Alkyne Insertion of 1,2,3-Benzotriazin-4(3H)-ones

Ru(II)-Catalyzed C-H Amination of 1,2,3-Benzotriazinones with Azide Compounds

A Ru(II)-catalyzed directed C-H amination of 1,2,3-benzotriazinones with azide compounds has been reported. The reaction has a wide substrate scope of organic azides with good results and represents a useful pathway to the construction of versatile heterocyclic amino products. In addition, the method can be used for the phthalazinones, highlighting the synthetic practicability of the strategy.

Continuous Flow Synthesis of Benzotriazin-4(3H)-ones via Visible Light Mediated Nitrogen-Centered Norrish Reaction

We report a new protocol for the synthesis of substituted benzotriazin-4(3H)-ones which are underrepresented heterocyclic scaffolds with important pharmacological properties. Our method exploits acyclic aryl triazine precursors that undergo a photocyclization reaction upon exposure to violet light (420 nm). Continuous flow reactor technology is exploited to afford excellent yields in only 10 min residence time with no additives or photocatalysts needed. The underlying reaction mechanism appears to be based on an unprecedented variation of the classical Norrish type II reaction with concomitant fragmentation and formation of N-N bonds. Scalability, process robustness, and green credentials of this intriguing transformation are highlighted.

Palladium-catalyzed denitrogenation/vinylation of benzotriazinones with vinylene carbonate

Herein, a novel Pd-catalyzed denitrogenation/vinylation of benzotriazinones using vinylene carbonate as the vinylation reagent is reported. This transformation demonstrates an unprecedented skeletal editing approach, effectively converting NN to CC fragments in situ and synthesizing a collection of isoquinolinones with broad-spectrum functional group tolerance. Moreover, the quite concise reaction system and late-stage modification of bioactive molecules comprehensively underscore the practical potential of this protocol.

Divergent Reactivity of 1,2,3-Benzotriazin-4(3H)-ones: Photocatalytic Synthesis of 3-Substituted Isoindolinones Achieved through a Nitrogen-Mediated Hydrogen Atom Shift

A regioselective visible-light-mediated denitrogenative alkene insertion of 1,2,3-benzotriazin-4(3H)-ones was developed to access 3-substituted isoindolinones, an important structural motif present in many biologically active molecules and natural products. Notably, divergent reactivity was achieved by switching from reported nickel catalysis (where C3-substituted 3,4-dihydroisoquinolin-1(2H)-ones form) to photocatalysis, where photocatalytic denitrogenation and a subsequent nitrogen-mediated hydrogen atom shift lead to exclusive 3-substituted isoindolinone formation. The developed photocatalytic reaction is compatible with activated terminal alkenes and cyclic α,β-unsaturated esters and ketones, with wide functional group tolerance for N-substitution of the 1,2,3-benzotriazin-4(3H)-ones. The utility of this procedure is highlighted by a gram-scale synthesis and postsynthetic amidation. To understand the origin of this unique product selectivity, experimental and computational mechanistic studies were performed.

p-Cresol-Enabled Nickel-Catalyzed Intermolecular Redox-Economical Coupling of Allyl Alcohols with Alkynes through oxa-Nickelacycle

An intermolecular redox-economical coupling reaction of allyl alcohols with alkynes, catalyzed by Ni-Brønsted acid cocatalysis, has been developed. This method allows for the synthesis of a diverse range of γ,δ-unsaturated ketones with yields ranging from 40% to 94%, while maintaining excellent compatibility with various functional groups. The transformation of the resulting product demonstrates the significant practical value of this method. Further mechanistic investigations have revealed that the reaction proceeds through the formation of an oxa-nickelacycle intermediate.

Nickel-Catalyzed Intramolecular Dual Annulation Reaction of Aryl Nitrile-Containing 1,2,3-Benzotriazin-4(3H)-ones: A Pathway To Synthesize Luotonin A and Related Polycyclic Pyrroloquinazolinones

Herein, we report a nickel-catalyzed intramolecular denitrogenative dual annulation reaction of aryl nitrile-containing 1,2,3-benzotriazine-4(3H)-ones to synthesize polycyclic pyrroloquinazolinones with a tolerance of a wide diversity of substituents. This catalytic reaction is the first denitrogenative transannulation of 1,2,3-benzotriazine-4(3H)-one with nitrile, which can be applied as the critical step to synthesize luotonin A with a high step economy.

Nickel-Catalyzed Functionalization Reactions Involving C-H Bond Activation via an Amidate-Promoted Strategy and Its Extension to the Activation of C-F, C-O, C-S, and C-CN Bonds

ConspectusThe development of functionalization reactions involving the activation of C-H bonds has evolved extensively due to the atom and step economy associated with such reactions. Among these reactions, chelation assistance has been shown to provide a powerful solution to the serious issues of reactivity and regioselectivity faced in the activation of C-H bonds. The vast majority of C-H functionalization reactions reported thus far has involved the use of precious metals. Kleiman and Dubeck reported the cyclonickelation of azobenzene and NiCp2 in which an azo group directs a Ni center to activate the ortho C-H bond in close proximity. Although this stoichiometric reaction was discovered earlier than that for other transition-metal complexes, its development as a catalytic reaction was delayed. No general catalytic systems were available for Ni-catalyzed C-H functionalization reactions for a long time. This Account details our group's development of Ni(0)- and Ni(II)-catalyzed chelation-assisted C-H functionalization reactions. It also highlights how the new strategy can be extended to the activation of other unreactive bonds.In the early 2010s, we found that the Ni(0)-catalyzed reaction of aromatic amides that contain a 2-pyridinylmethylamine moiety as a directing group with alkynes results in C-H/N-H oxidative annulation to give isoquinolinones. In addition, the combination of a Ni(II) catalyst and an 8-aminoquinoline directing group was found to be a superior combination for developing a wide variety of C-H functionalization reactions with various electrophiles. The reactions were proposed to include the formation of unstable Ni(IV) and/or Ni(III) species; the generation of such high-valence Ni species was rare at that time, but since then, many papers dealing with DFT and organometallic studies have appeared in the literature in attempts to understand the mechanism. Based on our in-depth considerations of the mechanism with respect to why an N,N-bidentate directing group is required, we realized that the formation of a N-Ni bond by the oxidative addition of a N-H bond to a Ni(0) species or a ligand exchange between a N-H bond and Ni(II) species is the key step. We concluded that the precoordination of the N(sp2) atom in the directing group positions the Ni species to be in close proximity to the N-H bond which permits the formation of a N-Ni bond. Based on this working hypothesis, we carried out the reaction using KOtBu as a base and found that the Ni(0)-catalyzed reaction of aromatic amides that do not contain such a specific directing group with alkynes results in the formation of the desired isoquinolinone, in which an amidate anion acts as the actual directing group. Remarkably, this strategy was found to be applicable to the activation of various other unreactive bonds such as C-F, C-O, C-S, and C-CN.

Regioselective Synthesis of 3-Substituted Isocoumarin-1-imines via Palladium-Catalyzed Denitrogenative Transannulation of 1,2,3-Benzotriazin-4(3H)-ones and Terminal Alkynes

A palladium-catalyzed denitrogenative transannulation strategy to access various 3-substituted isocoumarin-1-imine frameworks using 1,2,3-benzotriazin-4(3H)-ones and terminal alkynes is described. The reaction is highly regioselective and tolerates a wide range of functional groups. The reaction is believed to proceed via a five-membered palladacycle intermediate extruding environmentally benign molecular nitrogen as a by-product. The utility of this method was showcased through the one-pot synthesis of biologically relevant 3-substituted isocoumarin scaffolds.

Electrochemical annulation of 1,2,3-benzotriazinones with alkynes to access isoquinolin-1(2H)-ones

An eco-friendly approach for electrochemical radical cascade annulation of 1,2,3-benzotriazinones with alkynes is described. Under catalyst-free and external reductant-free electrolysis conditions, a range of isoquinolin-1(2H)-ones were obtained in moderate to good yields. Cyclic voltammetry and control studies suggest that the reaction proceeds via a radical pathway. Furthermore, this approach could be easily scaled up.

Mechanoredox/Nickel Co-Catalyzed Cross Electrophile Coupling of Benzotriazinones with Alkyl (Pseudo)halides

An air-tolerant mechanoredox/nickel cocatalyzed cross electrophile coupling of benzotriazinones with alkyl (pseudo)halides is developed by liquid-assisting grinding in the presence of manganese powders and strontium titanate as a reductant and a cocatalyst, respectively. Mechanical activation of metal surfaces via ball milling eliminates the chemical activator for manganese, while mechanoredox cocatalysis of strontium titanate remarkably improves the aryl/alkyl cross electrophile coupling via piezoelectricity-mediated radical generation from alkyl halides. Both benzotriazinones and alkyl (pseudo)halides display reactivities in the mechanoredox/nickel cocatalysis different from those of conventional thermal chemistry in solution. The scope of the reaction is demonstrated with 26 examples, showing a high chemoselectivity of bromides vs chlorides.

Synthesis of ortho-Methylated Benzamides via Palladium-Catalyzed Denitrogenative Cross-Coupling Reaction of [1,2,3]-Benzotriazin-4(3H)-ones with DABAL-Me3

We herein developed a palladium-catalyzed reaction of [1,2,3]-benzotriazin-4(3H)-ones with DABAL-Me₃ [bis(trimethylaluminum)-1,4-diazabicyclo[2.2.2]octane adduct], a cheap, stable, and solid organoaluminum reagent. In the presence of Pd(OAc)₂/XantPhos as a commercially available catalyst, [1,2,3]-benzotriazin-4(3H)-ones underwent denitrogenative coupling with DABAL-Me₃ to afford a wide array of N-aryl amides derived from ortho-methylated carboxylic acids. Under the same catalytic conditions, ortho-ethylation of [1,2,3]-benzotriazin-4(3H)-ones could also be achieved by using triethylaluminum.

Convenient Synthesis of Salicylanilide Sulfonates from 1,2,3-Benzotriazin-4(3H)-ones and Organosulfonic Acids via Denitrogenative Cross-Coupling

An efficient and straightforward approach to synthesize salicylanilide aryl and alkyl sulfonates from 1,2,3-benzotriazin-4(3H)-ones and organosulfonic acids is described. This protocol is operationally simple and scalable, exhibits a broad substrate scope with high functional group tolerance, and affords the desired products in good to high yield. Application of the reaction is also demonstrated by converting the desired product to synthetically useful salicylamides in high yields.

Visible-light promoted intramolecular carboamination of alkynes for the synthesis of oxazolidinone-fused isoquinolinones

An efficient method for the synthesis of isoquinolinone derivatives via photopromoted carboamination of alkynes is developed. Starting from the readily available propargyl alcohol derivatives, the polycyclic isoquinolinone derivatives could be obtained with good aryl and heterocycle tolerance. Both terminal and alkyl substituted alkynes could be employed. This protocol is operationally easy, and easily conducted on a gram-scale. A possible mechanism involving radical addition and cyclization following aromatization was proposed.

Transition-Metal-Catalyzed Denitrogenative Annulation to Access High-Valued N-Heterocycles

Over the past few years, the development of efficient methods to construct high-valued N-heterocyclic molecules have received massive attention owing to their extensive application in the areas of medicinal chemistry, drug discovery, natural product synthesis and so on. To access those high-valued N-heterocycles, many methods have been developed. In this context, transition-metal-catalyzed denitrogenative annulation of 1,2,3-triazoles and 1,2,3,4-tetrazoles has appeared as a powerful synthetic tool because it offers a step- and atom-economical route for the preparation of the nitrogen-rich molecules. Compared with the denitrogenative annulation of various 1,2,3-triazole frameworks, annulation of 1,2,3,4-tetrazole remains more challenging due to the inertness of the tetrazole moiety. This Review summarizes the significant achievements made in the field of denitrogenative annulation of various 1,2,3-triazoles and 1,2,3,4-tetrazoles including some pioneering examples in this area of research. We anticipate that this denitrogenative annulation reaction will find broad applications in the pharmaceutical industry, drug discovery and other fields of medicinal chemistry.

Nickel-Catalyzed Cross-Electrophile Coupling of 1,2,3-Benzotriazin-4(3H)-ones with Aryl Bromides

The nickel-catalyzed cross-electrophile coupling of 1,2,3-benzotriazin-4(3H)-ones with aryl bromides to generate a diverse array of ortho-arylated benzamide derivatives has been developed. The reaction displayed good functional group tolerance with Zn as the reductant. The key to this transformation is the ring opening of benzotriazinones, which undergo a denitrogenative process to obtain various benzamide derivatives (29 examples, 42-93% yield). The scalability of this transformation was demonstrated.

Trifluoroacetic Acid-Mediated Denitrogenative ortho-Hydroxylation of 1,2,3-Benzotriazin-4(3H)-ones: A Metal-Free Approach

An efficient trifluoroacetic acid-mediated denitrogenative hydroxylation of 1,2,3-benzotriazin-4(3H)-ones is described. This metal-free approach is compatible with a wide range of 1,2,3-benzotriazin-4(3H)-ones, affording ortho-hydroxylated benzamides in good to high yields with a short reaction time. The reaction is believed to proceed via a benzene diazonium intermediate. The synthetic utility of the reaction was successfully demonstrated by the preparation of an antimicrobial drug, Riparin C, and benzoxazine-2,4(3H)-diones in good yields.

Visible-Light-Promoted Denitrogenative Ortho-selenylation Reaction of benzotriazinones: Synthesis of ortho-selenylated Benzamides, Ebselen Analogs

A visible-light-promoted regioselective denitrogenative cross-coupling between benzotriazinones and selenosulfonates is reported. This protocol allows for the convenient synthesis of ortho-selenylated benzamides in good yields from readily available starting materials under...

1,2-Difunctionalizations of alkynes entailing concomitant C–C and C–N bond-forming carboamination reactions

Vicinal carboamination of alkynes is a highly reliable and efficient practical strategy for the quick preparation of valuable and diverse amine derivatives starting from simple synthons. The last decade has witnessed numerous practical methods employing transition-metal-based/metal-free carboamination approaches using alkynes for the synthesis of these N-bearing entities. Driven by the renaissance of transition metal catalysis, intermolecular and intramolecular carboamination of alkynes comprising concomitant C–N and C–C bond formation has been studied extensively. In contrast to metal catalysis, though analogous metal-free approaches have been relatively less explored in the literature, they serve as alternatives to these expensive approaches. Despite this significant progress, reviews documenting such examples are sporadic; as a result, most reports of this type remained scattered throughout the literature, thereby hampering further developments in this escalating field. In this review, different conceptual approaches will be discussed and examples from the literature will be presented. Further, the reader will get insight into the mechanisms of different transformations.

The 1,2-difunctionalization of alkynes happening through concomitant C–C and C–N bond formation strategies have provide an unified access to diversely functionalized N-bearing heterocycles.

Road Map for the Construction of High-Valued N-Heterocycles via Denitrogenative Annulation

The pursuit for the discovery of new and powerful synthetic methods to access high-value N-heterocycles has been at the forefront of organic chemistry research for more than a century. Considering the importance of N-scaffolds in modern science, over the past few decades, great research efforts have been made to develop efficient synthetic methods for the construction of nitrogen-rich molecules. Among many efforts, transition metal catalyzed denitrogenative annulation reaction has emerged as a cornerstone due to its innate versatility and wider scope of application.The denitrogenative annulation approach offers clear advantages over many existing methods, as it enables effective, single-step interconversion of easily available feedstocks into a variety of other important N-containing heterocyclic frameworks. Recently, transition metal catalyzed denitrogenative annulation reaction of the 1,2,3-triazole via a metal carbene intermediate sparked significant interest in the application of various important heterocycle syntheses. Denitrogenative annulation reaction of 1,2,3-triazoles proceeds via an ionic mechanism. Recently, we demonstrated a new concept for the denitrogenative reaction of triazoles with alkenes and alkynes via in situ generated 2-(diazomethyl)pyridines. The method takes advantage of the inherent properties of a Co(III)-carbene radical intermediate and is the first report of the denitrogenative annulation/cyclopropanation by a radical-activation mechanism.On the other hand, in contrast to the denitrogenative annulation of 1,2,3-triazole, annulation reaction of 1,2,3,4-tetrazole (a surrogate of azide having an important pyridyl unit) via metal nitrene remains a big challenge. Previously, flash vacuum pyrolysis studies had been used for nitrene-nitrene rearrangement of 1,2,3,4-tetrazole at high temperature. This Account summarizes our recent efforts in developing transition metal catalyzed denitrogenative annulation of 1,2,3-triazoles via a radical mechanism and 1,2,3,4-tetrazoles via metal nitrene to access important nitrogen-rich molecules. We demonstrated that the 1,2,3,4-tetrazole under Ir-catalyzed reaction conditions can produce a productive Ir-nitrene intermediate that can successfully be employed for the construction of a wide number of α-carbolines and 7-azaindoles. Moreover, we developed an iron-based unique strategy for the intermolecular denitrogenative annulation reaction between tetrazoles and alkynes. The reaction overcomes the traditional click reaction and proceeds via an unprecedented metalloradical activation mechanism. Furthermore, we used our understanding of tetrazole reactivity to design an iron-catalyzed intramolecular denitrogenative C(sp³)-H amination reaction of primary, secondary, and tertiary centers by using a metalloradical activation concept. At the same time, we also developed a general catalytic method to enable two distinct reactions (1,3-cycloaddition and denitrogenative annulation) using Mn(TPP)Cl that afforded two different classes of nitrogen heterocycles. Mechanistic studies showed that although the click reaction likely proceeds through an ionic mechanism and the denitrogenative annulation reaction likely proceeds via an electrophilic metallonitrene intermediate rather than a metallonitrene radical intermediate. Finally, we report an iron-catalyzed rearrangement reaction (ring expansion/migration) that proceeded with an unprecedented level of selectivity, reactivity, and functional group tolerance offering rapid access to numerous complex N-heterocycles. We believe that our continuous efforts in this field would be beneficial for pharmaceutical industries, drug discovery, and other fields of medicinal chemistry.

One-pot synthesis of N-substituted benzannulated triazoles via stable arene diazonium salts

A mild and effective one-pot synthesis of 1,2,3-benzotriazin-4(3H)-ones and benzothiatriazine-1,1(2H)-dioxide analogues has been developed. The method involves the diazotisation and subsequent cyclisation of 2-aminobenzamides and 2-aminobenzenesulfonamides via stable diazonium salts, prepared using a polymer-supported nitrite reagent and p-tosic acid. The transformation was compatible with a wide range of aryl functional groups and amide/sulfonamide-substituents and was used for the synthesis of pharmaceutically important targets. The synthetic utility of the one-pot diazotisaton-cyclisation process was further demonstrated with the preparation of an α-amino acid containing 1,2,3-benzotriazin-4(3H)-one.

Rh(III)-Catalyzed three-component cascade annulation to produce the N-oxopropyl chain of isoquinolone derivatives

Developing powerful methods to introduce versatile functional groups at the N-substituents of isoquinolone scaffolds is still a great challenge. Herein, we report a novel three-component cascade annulation reaction to efficiently construct the N-oxopropyl chain of isoquinolone derivatives via rhodium(iii)-catalyzed C-H activation/cyclization/nucleophilic attack, with oxazoles used both as the directing group and potential functionalized reagents.

Cobalt-catalyzed coupling reactions of 2-halobenzamides with alkynes: investigation of ligand-controlled dual pathways

The Co-catalyzed reactions of 2-halobenzamides and alkynes to form quinolinones or 2-vinyl benzamides are described here. These two reactions can be controlled merely by ligands.

Synthesis of ortho-arylated and alkenylated benzamides by palladium-catalyzed denitrogenative cross-coupling reactions of 1,2,3-benzotriazin-4(3H)-ones with organoboronic acids

An efficient palladium-catalyzed denitrogenative cross-coupling reaction of 1,2,3-benzotriazin-4(3H)-ones with organoboronic acids is described. The reaction affords various ortho-aryl and alkenylated benzamides in good to high yields.

Nickel-catalyzed C-O/N-H, C-S/N-H, and C-CN/N-H annulation of aromatic amides with alkynes: C-O, C-S, and C-CN activation

The Ni-catalyzed reaction of ortho-phenoxy-substituted aromatic amides with alkynes in the presence of LiO^tBu as a base results in C–O/N–H annulation with the formation of 1(2H)-isoquinolinones. The use of a base is essential for the reaction to proceed. The reaction proceeds, even in the absence of a ligand, and under mild reaction conditions (40 °C). An electron-donating group on the aromatic ring facilitates the reaction. The reaction was also applicable to carbamate (C–O bond activation), methylthio (C–S bond activation), and cyano (C–CN bond activation) groups as leaving groups.

The Ni-catalyzed reaction of ortho-phenoxy-substituted aromatic amides with alkynes in the presence of LiO^tBu as a base results in C–O/N–H annulation with the formation of 1(2H)-isoquinolinones.

Rhodium-catalyzed synthesis of substituted isoquinolones via a selective decarbonylation/alkyne insertion cascade of phthalimides

A rhodium-catalyzed decarbonylation/alkyne insertion cascade of phthalimides has been established. The reaction can be carried out in an operationally simple manner and provides expedient access to a series of isoquinolones in moderate to good yields. This reaction proceeded through a sequential decarbonylation/alkyne insertion/intramolecular annulation procedure and featured good functional group tolerance, ample substrate scope, and the construction of C-C and C-N bonds in one pot.

Isoquinolone Synthesis via Zn(OTf)2-Catalyzed Aerobic Cyclocondensation of 2-(1-Alkynyl)-benzaldehydes with Arylamines

A zinc(II) triflate-catalyzed cyclocondensation of ortho-alkynylbenzaldehydes with arylamines in the presence of base under an oxygen atmosphere affording isoquinolones in good to high yields has been developed. The advantages of the present catalyst system include the use of an air-stable and cheap commercially available Lewis acid as the catalyst, high atom utilization and easily available starting materials.

Bifunctional Phosphine Ligand-Enabled Gold(I)-Catalyzed O-Nucleophilic Addition of N-Hydroxybenzo[1,2,3]-triazin-4(3H)-ones to Alkynes Followed by [3,3]-Rearrangement: Simultaneous Formation of C-O and C-N Bonds

We describe a gold (I)-catalyzed tandem O-nucleophilic addition/[3,3]-rearrangement reaction of N-hydroxybenzo[1,2,3]-triazin-4(3H)-ones with alkynes enabled by a biphenyl-2-yl phosphine ligand featuring a pendant amide moiety (L1). A variety of 1-(2-oxo-2-arylethyl)benzo [d][1,2,3]triazin-4(1H)-one derivatives were synthesized in good to excellent yields. The present protocol gives a rare example of simultaneous formation of C-O and C-N bonds in the gold(I)-catalyzed [3,3]-sigmatropic rearrangements.

Recent advances and prospects in nickel-catalyzed C–H activation

Nickel-catalyzed C–H activation has become a predominant and ubiquitous research area in organic chemistry.

Regioselective cycloaddition of potassium alkynyltrifluoroborates with 3-azetidinones and 3-oxetanone by nickel-catalysed C–C bond activation

The nickel-catalysed (4+2) cycloaddtion of potassium alkynyltrifluoroborates and 3-azetidinones and 3-oxetanone gives only one regioisomer for all alkyne substituents.

Palladium-catalyzed decarbonylative annulation of phthalimides with arynes: direct construction of phenanthridinones

A novel palladium-catalyzed decarbonylative annulation between phthalimides and arynes was well-established, affording phenanthridinone derivatives in moderate to good yields.