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We report here a formal insertion of a metal carbene complex in a single carbon‐carbon bond. This behavior occurs with the participation of an α‐imino gold carbene complex, generated from benzofused triazapentalenes or, in a one‐pot procedure, from their 1‐propargyl‐1H‐benzotriazole precursors, and gold‐catalytically activated ynamides. As the result, 3H‐indole derivatives were obtained, with formation of a quaternary center. A computational analysis carried out on the reaction mechanism indicates that the bulkiness of the gold ligand plays a key role forcing a conformation, which includes aromatic interactions, that favors the approximation of the carbenic carbon to the reactive site. In addition, a negative crossover experiment rules out a cationic arene migration pathway. [ABSTRACT FROM AUTHOR]

1,3-butadiynamides—the ethynylogous variants of ynamides—receive considerable attention as precursors of complex molecular scaffolds for organic and heterocyclic chemistry. The synthetic potential of these C4-building blocks reveals itself in sophisticated transition-metal catalyzed annulation reactions and in metal-free or silver-mediated HDDA (Hexa-dehydro-Diels–Alder) cycloadditions. 1,3-Butadiynamides also gain significance as optoelectronic materials and in less explored views on their unique helical twisted frontier molecular orbitals (Hel-FMOs). The present account summarizes different methodologies for the synthesis of 1,3-butadiynamides followed by the description of their molecular structure and electronic properties. Finally, the surprisingly rich chemistry of 1,3-butadiynamides as versatile C4-building blocks in heterocyclic chemistry is reviewed by compiling their exciting reactivity, specificity and opportunities for organic synthesis. Besides chemical transformations and use in synthesis, a focus is set on the mechanistic understanding of the chemistry of 1,3-butadiynamides—suggesting that 1,3-butadiynamides are not just simple alkynes. These ethynylogous variants of ynamides have their own molecular character and chemical reactivity and reflect a new class of remarkably useful compounds. [ABSTRACT FROM AUTHOR]

We report herein intramolecular (3+2) cycloaddition reactions between ynamides as three‐atom components and benzyne. In these intramolecular reactions, the two‐bond formation is realized by exploiting benzyne precursors that contain a chlorosilyl group as a linking functionality. This method thus highlights the ambivalent character of the intermediate indolium ylide, which exhibits both nucleophilic and electrophilic properties at its C2 atom. [ABSTRACT FROM AUTHOR]

We report herein intramolecular (3+2) cycloaddition reactions between ynamides as three‐atom components and benzyne. In these intramolecular reactions, the two‐bond formation is realized by exploiting benzyne precursors that contain a chlorosilyl group as a linking functionality. This method thus highlights the ambivalent character of the intermediate indolium ylide, which exhibits both nucleophilic and electrophilic properties at its C2 atom. [ABSTRACT FROM AUTHOR]

Herein, an I2‐catalyzed unprecedented cycloisomerization of ynamides is developed, furnishing various functionalized bis(indole) derivatives in generally good to excellent yields with wide substrate scope and excellent atom‐economy. This protocol not only represents the first molecular‐iodine‐catalyzed tandem complex alkyne cycloisomerizations, but also constitutes the first chemoselective cycloisomerization of tryptamine‐ynamides involving distinctively different C(sp3)−C(sp3) bond cleavage and rearrangement. Moreover, chiral tetrahydropyridine frameworks containing two stereocenters are obtained with moderate to excellent diastereoselectivities and excellent enantioselectivities. Meanwhile, cycloisomerization and aromatization of ynamides produce pyrrolyl indoles with high efficiency enabled by I2. Additionally, control experiments and theoretical calculations reveal that this reaction probably undergoes a tandem 5‐exo‐dig cyclization/rearrangement process. [ABSTRACT FROM AUTHOR]

Herein, an I2‐catalyzed unprecedented cycloisomerization of ynamides is developed, furnishing various functionalized bis(indole) derivatives in generally good to excellent yields with wide substrate scope and excellent atom‐economy. This protocol not only represents the first molecular‐iodine‐catalyzed tandem complex alkyne cycloisomerizations, but also constitutes the first chemoselective cycloisomerization of tryptamine‐ynamides involving distinctively different C(sp3)−C(sp3) bond cleavage and rearrangement. Moreover, chiral tetrahydropyridine frameworks containing two stereocenters are obtained with moderate to excellent diastereoselectivities and excellent enantioselectivities. Meanwhile, cycloisomerization and aromatization of ynamides produce pyrrolyl indoles with high efficiency enabled by I2. Additionally, control experiments and theoretical calculations reveal that this reaction probably undergoes a tandem 5‐exo‐dig cyclization/rearrangement process. [ABSTRACT FROM AUTHOR]

An efficient radical cyclization of suitably functionalized ynamides to nitrogen-containing heterocycles is reported. Upon reaction with tributyltin hydride in the presence of catalytic amounts of AIBN in toluene at 80 °C, a range of ynamides bearing a N -iodopropyl chain could be smoothly cyclized, in a highly regio- and stereoselective manner, to the corresponding 2-arylidenepyrrolidines in good to excellent yields. The exocyclic double bond was in addition shown to be an excellent anchor for further chemical diversification and the generality of this radical cyclization could be highlighted by its extension to the synthesis of other nitrogen heterocycles including piperidines, azepanes, pyrazolidines and hexahydropyridazines. [ABSTRACT FROM AUTHOR]

In recent years, asymmetric catalysis of ynamides has attracted much attention, but these reactions mostly constructed central chirality, except for a few examples on the synthesis of axially chiral compounds which exclusively relied on noble‐metal catalysis. Herein, a facile access to axially chiral N‐heterocycles enabled by chiral Brønsted acid‐catalyzed 5‐endo‐dig cyclization of ynamides is disclosed, which represents the first metal‐free protocol for the construction of axially chiral compounds from ynamides. This method allows the practical and atom‐economical synthesis of valuable N‐arylindoles in excellent yields with generally excellent enantioselectivities. Moreover, organocatalysts and ligands based on such axially chiral N‐arylindole skeletons are demonstrated to be applicable to asymmetric catalysis. [ABSTRACT FROM AUTHOR]

In recent years, asymmetric catalysis of ynamides has attracted much attention, but these reactions mostly constructed central chirality, except for a few examples on the synthesis of axially chiral compounds which exclusively relied on noble‐metal catalysis. Herein, a facile access to axially chiral N‐heterocycles enabled by chiral Brønsted acid‐catalyzed 5‐endo‐dig cyclization of ynamides is disclosed, which represents the first metal‐free protocol for the construction of axially chiral compounds from ynamides. This method allows the practical and atom‐economical synthesis of valuable N‐arylindoles in excellent yields with generally excellent enantioselectivities. Moreover, organocatalysts and ligands based on such axially chiral N‐arylindole skeletons are demonstrated to be applicable to asymmetric catalysis. [ABSTRACT FROM AUTHOR]

Described herein is a novel Brønsted acid catalyzed intramolecular hydroalkoxylation/Claisen rearrangement, allowing the practical and atom‐economic synthesis of a range of valuable spirolactams from readily available ynamides in generally good to excellent yields with excellent diastereoselectivities and broad substrate scope. Importantly, an unexpected dearomatization of nonactivated arenes and heteroaromatic compounds is involved in this tandem sequence. Moreover, an asymmetric version of this tandem cyclization was also achieved by efficient kinetic resolution by chiral phosphoric acid catalysis. In addition, the [3,3]‐rearrangement is shown to be kinetically preferred over the related [1,3]‐rearrangement by theoretical calculations. [ABSTRACT FROM AUTHOR]

Described herein is a novel Brønsted acid catalyzed intramolecular hydroalkoxylation/Claisen rearrangement, allowing the practical and atom‐economic synthesis of a range of valuable spirolactams from readily available ynamides in generally good to excellent yields with excellent diastereoselectivities and broad substrate scope. Importantly, an unexpected dearomatization of nonactivated arenes and heteroaromatic compounds is involved in this tandem sequence. Moreover, an asymmetric version of this tandem cyclization was also achieved by efficient kinetic resolution by chiral phosphoric acid catalysis. In addition, the [3,3]‐rearrangement is shown to be kinetically preferred over the related [1,3]‐rearrangement by theoretical calculations. [ABSTRACT FROM AUTHOR]

The combination of a nucleophilic nitrene equivalent, a triple bond and a π‐acid catalyst has underpinned numerous efficient transformations for the preparation of azacycles. This personal account details our efforts in developing an annulation strategy. Adding a nucleophilic nitrenoid to an activated alkyne can generate carbenoid character that is then quenched by a cyclisation onto the nitrenoid substituent. The use and development of N‐acyl and N‐heterocyclic pyridinium‐N‐aminides as 1,3‐N,O and 1,3‐N,N‐dipole equivalents is discussed in the context of oxazole and heterocycle‐fused imidazole formation, respectively. The resulting processes are highly efficient, practically straightforward, and tolerate considerable structural and functional group variation. Our use of heteroatom‐substituted alkynes as enabling tools for reaction discovery is discussed. The reactivity accessed from the strong donor‐like properties of ynamides is complemented by that obtained from alkynyl thioethers, which are emerging as interesting substrates for π‐acid catalysis. [ABSTRACT FROM AUTHOR]

Ynamide, a unique species with inherited polarization of nitrogen lone pair electron to triple bond, has been largely used for the developement of novel synthetic methods and the construction of unusual N‐bearing heterocycles. The reaction versatility of ynamide on umpolung reactivity, radical reactions and asymmetric synthesis have been recently reviewed. This review provides an overall scenic view into the gold catalyzed transformation of ynamides. The ynamides reactivity towards nitrogen‐transfer reagents, such as azides, nitrogen ylides, isoxazoles, and anthranils; oxygen atom‐transfer reagents, like nitrones, sulfoxides, and pyridine N‐oxides; and carbon nucleophiles under gold catalysis are herein uncovered. The scope as well the mechanistic insights of each reaction is also briefed. [ABSTRACT FROM AUTHOR]

Nitrogen‐substituted alkynes, such as ynamines and ynamides, are versatile synthetic building blocks. Ynimines bearing additional nucleophilic and electrophilic centers relative to ynamines and ynamides are expected to have high synthetic potential. However, their chemical reactivity remains unexplored owing mainly to the lack of synthetic accessibility. We report herein a versatile copper‐catalyzed synthesis of ynimines from readily available O‐acetyl ketoximes and terminal alkynes. A wide range of O‐acetyl ketoximes derived from diaryl ketones, aryl alkyl ketones and dialkyl ketones underwent cross‐coupling with a diverse set of terminal alkynes to afford the ynimines in good to excellent yields. An unprecedented [5+1] heteroannulation reaction exploiting the reactivity of the ynimine generated in situ was subsequently developed for the synthesis of medicinally important heterocycles, including isoquinolines, azaindoles, azabenzofurans, azabenzothiophenes and carbolines. [ABSTRACT FROM AUTHOR]

Nitrogen‐substituted alkynes, such as ynamines and ynamides, are versatile synthetic building blocks. Ynimines bearing additional nucleophilic and electrophilic centers relative to ynamines and ynamides are expected to have high synthetic potential. However, their chemical reactivity remains unexplored owing mainly to the lack of synthetic accessibility. We report herein a versatile copper‐catalyzed synthesis of ynimines from readily available O‐acetyl ketoximes and terminal alkynes. A wide range of O‐acetyl ketoximes derived from diaryl ketones, aryl alkyl ketones and dialkyl ketones underwent cross‐coupling with a diverse set of terminal alkynes to afford the ynimines in good to excellent yields. An unprecedented [5+1] heteroannulation reaction exploiting the reactivity of the ynimine generated in situ was subsequently developed for the synthesis of medicinally important heterocycles, including isoquinolines, azaindoles, azabenzofurans, azabenzothiophenes and carbolines. [ABSTRACT FROM AUTHOR]

Research on the synthesis of heterocyclic scaffolds is an important challenge in organic synthesis because heterocycles are an important block in the structure of many drugs and pharmaceutical molecules. Ynamides are one the most versatile and enabling building blocks in organic synthesis because they have recently used starting materials for the construction of multifunctional compounds especially heterocyclic compounds. In recent times, a number of catalytic systems have been reported in the literature for the synthesis of heterocyclic scaffolds from ynamide derivatives. This review has outlined the extensive application of ynamide derivatives in the synthesis of a library of heterocyclic scaffolds. Based on Ynamides: catalysis in the synthesis of heterocyclic scaffolds [ABSTRACT FROM AUTHOR]

Ynamides are electron‐rich heteroatom‐substituted alkynes with C−C triple bond directly tethered to the amide group. Over the past decades, ynamides have proven to be versatile reagents for organic synthesis and have received extensive attention. Compared with the well‐established ionic reactions of ynamides, radical‐based ynamide reactions have been exploited relatively seldom. Herein, radical reactions of ynamides, classified by radical attack at the α‐position and β‐position of ynamides, are reviewed by highlighting the reaction selectivity, scope, mechanism, and applicability. The aim of this review is to provide a comprehensive summarization of these advances, casting light on the further development of ynamide chemistry. [ABSTRACT FROM AUTHOR]

Summary of main observation and conclusion: An efficient copper‐catalyzed carbocyclization of silyl enol ether tethered ynamides has been developed, allowing rapid and practical construction of diverse 2‐azabicyclo[3.2.0] compounds in generally good to excellent yields with broad substrate scope under mild reaction conditions. Importantly, this protocol not only constitutes a rare example of non‐noble metal‐catalyzed alkyne carbocyclization, but also represents a rare cyclization on the β‐position of π‐tethered ynamides. The possibility of asymmetric carbocyclization via kinetic resolution also emerges. [ABSTRACT FROM AUTHOR]

The gold‐catalyzed interplay between cyanamides and ynamides demonstrates condition‐dependent mechanistic dichotomy. [2+2+2] Cycloaddition proceeds under kinetically controlled conditions to give 2,4,6‐triaminopyrimidines (19 examples, up to 99%). Under thermodynamically controlled conditions, the reactivity switches from [2+2+2]‐ to [4+2] cycloaddition; the latter [4+2] reaction accomplishes 1,3‐diaminoisoquinolines (19 examples, up to 97%). The advantages of both methods include regioselectivity, mild reaction conditions (even for the thermodynamically controlled [4+2] reaction) and the possibility of introducing a variety of dialkyl, diaryl, and heterocyclic amino substituents into the target pyrimidine and isoquinoline cores. The reactions were conducted on gram scales and the versatility of the obtained products was demonstrated by post‐functionalizations. [ABSTRACT FROM AUTHOR]

Functionalised N‐heterocyclic pyridinium N‐aminides have been designed and synthesised to evaluate a nitrenoid‐based annulation strategy into imidazole‐fused oxo‐substituted frameworks of importance to medicinal and agrochemical discovery programmes. Sulfenyl substituted ynamides were identified as privileged reactants affording productive gold‐catalysed annulation reactions with these and other nitrenoids. This annulation method provides selective and efficient access into geminally amino‐sulfenyl substituted nitrogen heterocycles under mild reaction conditions. [ABSTRACT FROM AUTHOR]

A smooth, gold catalyzed, atom‐economical and regioselective synthesis of indoles is reported here. The reaction occurs from a nucleophilic attack of in situ synthesized triazapentalenes to gold activated ynamides and involves the participation of α‐imino gold carbene complexes. The use of sulfonyl ynamides drives the reaction to the formation of 2‐amidosubstituted indoles. However, the employment of 2‐oxazolidinolylynamides allows the formation of both isomers, such as, 2‐amido‐ and 3‐amidosubstituted indoles. In this case, the regioselection could be controlled by a correct choice of the catalyst ligand and the electron‐donating capability of the aryl substituent of the ynamide. A correct control in both parameters permits a totally regioselective synthesis of one or the other regioisomer. Isolation of key intermediates and X‐ray analysis allowed for a plausible explanation for this behavior. [ABSTRACT FROM AUTHOR]

Abstract: A gold‐catalyzed intermolecular [4+2] annulation of easily accessible 2‐ethynylanilines with ynamides offers a highly region‐selective, modular, efficient, and atom‐economical strategy for the synthesis of substituted 2‐aminoquinolines in up to 93% yield. [ABSTRACT FROM AUTHOR]

Abstract: Ynamides, as versatile synthetic precursors, have attracted much attention from synthetic chemists and sparked the development of a number of methodologies for the construction of various structures. 1H‐Pyrrolo[2,3‐d]carbazole is a core scaffold of a series of monoterpene indole alkaloids found in Kopsia, Strychnos, and Aspidosperma, for example. In this study, 1H‐pyrrolo[2,3‐d]carbazole derivatives were synthesized by a Brønsted acid‐catalyzed tandem cyclization starting from tryptamine‐based ynamides. This strategy prevented Wagner–Meerwein rearrangement by instantaneous intramolecular nucleophilic trapping of the indoleninium to afford a tetracyclic indoline via an in situ‐formed enol species induced by the formation of a more stable conjugate diene moiety. The functional group tolerances were investigated by using a series of readily available substrates. A plausible mechanism has been proposed based on the evidence of the capture of the hemiaminal intermediate. Lastly, a Büchi ketone, which is the pivotal intermediate in the synthesis of the indole alkaloid vindorosine, was synthesized by utilizing our newly developed methodology. [ABSTRACT FROM AUTHOR]

Abstract: Organic synthesis boasts a wide array of reactions involving either radical species or ionic intermediates. The combination of radical and polar species, however, has not been explored to a comparable extent. Herein we present the hydrative aminoxylation of ynamides, a reaction which can proceed by either a polar‐radical crossover mechanism or through a rare cationic activation. Common to both processes is the versatility of the persistent radical TEMPO and its oxidised oxoammonium derivative TEMPO+. The unique mechanisms of these processes are elucidated experimentally and by in‐depth DFT‐calculations. [ABSTRACT FROM AUTHOR]

Stable ynamides are used for the development of novel synthetic transformations and the construction of unusual carbo/heterocycles. The intramolecular cyclization of π-tethered alkene/alkyne/alleneynamides is studied extensively for the fabrication of a wide range of molecular scaffolds for various applications. The ketene-acetal/aminal generated in situ from π-tethered ynamides participates in intramolecular cyclization/cycloisomerization processes to yield N-bearing fused heterocycles. This account summarizes the scientific merits and the advances made in cyclization and cycloisomerization strategies for stable π-tethered alkene/alkyne/allene-ynamides. 1 Introduction 2 π-Tethered Ynamides 3 Alkene-Tethered Ynamides 4 Alkyne-Tethered Ynamides 5 Allene-Tethered Ynamides 6 Concluding Remarks. [ABSTRACT FROM AUTHOR]

The first synthetic route to yndiamides, a novel class of double aza-substituted alkyne, has been established by the copper(I)-catalyzed cross-coupling of 1,1-dibromoenamides with nitrogen nucleophiles. The utility of these compounds is demonstrated in a range of transition-metal-catalyzed and acid-catalyzed transformations to afford a wide variety of 1,2-diamide functionalized products. [ABSTRACT FROM AUTHOR]

Abstract A gold-catalyzed intermolecular reaction of ynamides with 3-indolyl azides via the presumable α-imino gold carbenes has been developed, providing an alternative and efficient way for the synthesis of valuable 3-amino-β-carbolines in generally good to excellent yields. Importantly, this new protocol involves an unexpected 1,2-alkyl migration pathway. [ABSTRACT FROM AUTHOR]

Platinum-catalyzed formal [5+2] and [4+2] annulations of isoxazoles with heterosubstituted alkynes enabled the atom-economical synthesis of valuable 1,3-oxazepines and 2,5-dihydropyridines, respectively. Importantly, this Pt catalysis not only led to unique reactivity dramatically divergent from that observed under Au catalysis, but also proceeded via unprecedented α-imino platinum carbene intermediates. [ABSTRACT FROM AUTHOR]

A metal-free trimolecular [2+2+2] cycloaddition of internal ynamides and nitriles for de novo synthesis of fully substituted pyridines is disclosed. With the versatile Brønsted acid catalyst HNTf2, the mild intermolecular cyclotrimerization process proceeds with complementary chemoselectivity and excellent regioselectivity. [ABSTRACT FROM AUTHOR]

A diverse set of highly substituted 4-aminoquinolines was synthesized from ynamides, triflic anhydride, 2-chloropyridine, and readily accessible amides in a mild one-step procedure. [ABSTRACT FROM AUTHOR]

A novel method for metal-free oxothiolation of ynamides to construct oxazolidine-2,4-diones bearing sulfur-substituted quaternary carbon atoms has been developed. It represents a rare C−O bond cleavage of ynamides, as well as a facile and tandem approach for the formation of C−O, C−S, and C−Cl bonds. This redox-neutral protocol can be applied to the synthesis of multisubstituted oxazolidine-2,4-diones with good chemoselectivity and good yields of isolated products under mild conditions. [ABSTRACT FROM AUTHOR]

[1,4]Oxazino[3,2- b ]indoles as well as 1 H -pyrazino[2,3- b ]indoles are constructed in good to excellent yields via gold-catalyzed cascade cyclization of (azido)ynamides. The use of readily available starting materials, a simple procedure and mild reaction conditions are other significant features of this method. [ABSTRACT FROM AUTHOR]

Reported herein is the novel gold-catalyzed intermolecular [2+2+2] cycloaddition of ynamides with two discrete nitriles to form monomeric 4-aminopyrimidines, which are pharmaceutically important structural motifs. The utility of this new cycloaddition is demonstrated by the excellent regioselectivity obtained using a variety of ynamides and nitriles. [ABSTRACT FROM AUTHOR]

Two unprecedented N functionalizations of indoles with ynamides are described. By varying the electron-withdrawing group on the ynamide nitrogen atom, either Z-indolo-etheneamides or indolo-amidines can be selectively obtained under the same metal-free reaction conditions. The scope and synthetic potential of these reactions, as well as some mechanistic insights provided by DFT calculations, are reported. [ABSTRACT FROM AUTHOR]

A new synthetic route to the privileged 1,2-dihydroisoquinolines is reported. This method, which relies on a gold-catalyzed formal [4+2] cycloaddition between ynamides and imines, provides a new retrosynthetic disconnection of the 1,2-dihydroisoquinoline core by installing the 1,8a CC and 2,3 CN bonds in one step. Both aldimines and ketimines can be used as substrates. In addition, one example of dihydrofuropyridine synthesis is also demonstrated. [ABSTRACT FROM AUTHOR]

A series of arylynamides with alkyloxy groups at the ortho position of the aryl group was prepared through a short alkylation/cross-coupling/amidation sequence. The gold-catalyzed conversion of these substrates combined both CO and CC formation steps, thus providing benzofurans with amine functionalities at the 2-position and alkyl groups at the 3-position. Cross-over experiments showed that the alkyl-migration step was an intermolecular process. X-ray crystal-structure analysis of two of the products supported our structural assignment. In some cases, the corresponding benzofurans without the alkyl group at the 3-position were obtained as side-products, which were formed through a competing protodeauration process. [ABSTRACT FROM AUTHOR]

Hydrate your chemistry! Hydrative cyclization of 5‐yne‐ynamides in the presence of Echavarren's catalyst and p‐toluenesulphonic acid (PTSA)⋅H2O at room temperature affords an array of 1,6‐dihydropyridin‐2(3H)one derivatives. Isomerization, epoxidation, and hydrogenation of the double bond and insertion of an extended π‐conjugate system into the pyridinone skeleton have been successfully accomplished (see scheme; Ts=tosyl). [ABSTRACT FROM AUTHOR]

Abstract: Ynamides are tested as new partners in radical and organometallic transformations. A radical cascade involving a 5-exo-dig cyclization followed by a 6-endo-trig radical trapping transforms ynamides into hetero-polycyclic compounds such as isoindoles, isoindolinones and pyrido-isoindolones. Various ene–tosylynamides react with platinum(II) chloride and lead to bicyclic nitrogenated heterocycles. This unprecedented and easily operated process can be coupled with a hydrolysis of the intermediate cyclic tosylenamides in a one-pot transformation, which provides cyclobutanones. [Copyright &y& Elsevier]