Syntheses of vinylindoles via a Brønsted acid catalyzed highly regio- and stereoselective cis-hydroarylation of ynamides

A highly regio- and stereoselective Brønsted acid-catalyzed coupling of ynamides and indoles is described. This process is the equivalent of hydroarylation of ynamides and leads to the efficient syntheses of vinylindoles. Diels-Alder reaction between the vinylindoles and DMAD afforded carbazole derivatives in good yields.     

Synthesis of (Z)-β-(Carbonylamino)alkenylindium through Regioselective anti-Carboindation of Ynamides and Its Transformation to Multisubstituted Enamides

The regioselective anti-carboindation of ynamides by using InBr₃ and silylated nucleophiles was developed to synthesize (Z)-β-(carbonylamino)alkenylindiums. The X-ray crystallographic analysis of an alkenylindium suggested that the reaction proceeded in an anti-addition fashion. In contrast to reported syn-carbometalations of ynamides by using organometallics, a cooperation of InBr₃ and silylated nucleophiles to ynamides achieved an anti-addition, which was supported by DFT calculations. The scope of substrates included various ynamides and silylated nucleophiles, such as silyl ketene acetals and silyl ketene imines. The transformation of synthesized alkenylindiums by iodination, radical coupling, and Pd-catalyzed cross-coupling successfully afforded trisubstituted enamines with high regio- and stereoselectivities.     

Regioselective Difunctionalization and Annulation of Ynamide

The use of ynamides in organic synthesis has gained significant attention due to their ability to provide access to complex molecular structures through transformations such as 1,2-difunctionalization and annulation reactions. These reactions enable the formation of highly functionalized N-bearing olefins and unusual N-bearing heterocycles. In this minireview, we present a systematic overview of the regioselective difunctionalization and annulation reactions of ynamides. We discuss the multi-component reactions, and radical-triggered functionalizations across the ynamides carbon–carbon multiple bonds and the use of bifunctional reagents in annulation of ynamides, highlighting their potential in expanding the substrate scope. Furthermore, we provide insights into the mechanistic breakthroughs that have been achieved in recent years in the development of these reactions. Finally, we emphasize the promising future prospects of ynamides as versatile building blocks for the synthesis of complex molecular architectures.     

Umpolung Reactivity of Ynamides: An Unconventional [1,3]‐Sulfonyl and [1,5]‐Sulfinyl Migration Cascade

A regioselective sulfonyl/sulfinyl migration cycloisomerization cascade of alkyne‐tethered ynamides is developed in the presence of XPhosgold catalyst. This reaction is the first example of a general [1,3]‐sulfonyl migration from the nitrogen center to the β‐carbon atom of ynamides, followed by umpolung 5‐endo‐dig cyclization of the ynamide α‐carbon atom to the gold‐activated alkyne, and final deaurative [1,5]‐sulfinylation. This process allows the synthesis of peripherally decorated unconventional 4‐sulfinylated pyrroles with broad scope from N‐propargyl‐tethered ynamides. In contrast, N‐homopropargyl‐tethered ynamides undergo intramolecular tetradehydro Diels–Alder reaction to provide 2,3‐dihydro‐benzo[f]indole derivatives. Control experiments and density‐functional theory studies were used to study the reaction pathways.     

Pauson–Khand cycloaddition reactions of chiral ynamides. Observation of an unusual endo-addition with norbornadiene

Pauson–Khand cycloadditions using chiral ynamides are achieved in modest to good yields with excellent regioselectivity and modest stereoselectivity. An unusual endo addition is found when using norbornadiene and substituted ynamides, leading to cycloadducts that were not observed in previous studies using ynamides or ynamines.     

Synthesis of chiral allenes from ynamides through a highly stereoselective Saucy-Marbet rearrangement

A highly stereoselective Saucy-Marbet rearrangement using chiral ynamides and propargyl alcohols is described here. This rearrangement can be catalyzed by para-nitrobenzenesulfonic acid and leads to high diastereoselectivities for a range of different chiral propargyl alcohols and ynamides in a stereochemically intriguing matched, mismatched or indifferent manner. The stereoselective Saucy-Marbet rearrangement of ynamides provides an excellent entry to highly substituted chiral homo allenyl alcohols.     

Synthesis of alpha-keto-imides via oxidation of ynamides

A de novo preparation of alpha-keto-imides via ynamide oxidation is described. With a number of alkyne oxidation conditions screened, a highly efficient RuO2-NaIO4 mediated oxidation and a DMDO oxidation have been identified to tolerate a wide range of ynamide types. In addition to accessing a wide variety of alpha-keto-imides, the RuO2-NaIO4 protocol provides a novel entry to the vicinal tricarbonyl motif via oxidation of push-pull ynamides, and imido acylsilanes from silyl-substituted ynamides. Chemoselective oxidation of ynamides containing olefins can be achieved by using DMDO, while the RuO2-NaIO4 protocol is not effective. These studies provide further support for the synthetic utility of ynamides.     

Copper sulfate-pentahydrate-1,10-phenanthroline catalyzed amidations of alkynyl bromides. Synthesis of heteroaromatic amine substituted ynamides

A practical cross-coupling of amides with alkynyl bromides using catalytic CuSO(4).5H(2)O and 1,10-phenanthroline is described here. This catalytic protocol is more environmentally friendly than the use of CuCN or copper halides and provides a general entry for syntheses of ynamides including various new sulfonyl and heteroaromatic amine substituted ynamides. Given the interest in ynamides, this N-alkynylation of amides should be significant for the future of ynamides in organic synthesis.     

Copper-mediated synthesis of N-vinyl ynamides from N-vinyl carbamates

Ynamides are versatile 3-atoms building blocks for organic synthesis as they participate in a variety of ionic, radical and pericyclic processes. Converting ynamides into 5-atom building blocks, such as the yet unreported N-vinyl ynamides, would open new avenues in this fascinating chemistry. We describe herein our efforts towards such goal and demonstrate that the cross-coupling between N-vinyl carbamates and bromo-alkynes using copper(I) thiophene carboxylate, 1,10-phenanthroline and tBuOK in DMSO is a reactive system with an improved profile compared to the classical ynamides syntheses. The advantages and limitations of this copper-mediated reaction are discussed.     

Copper(II)-catalyzed amidations of alkynyl bromides as a general synthesis of ynamides and Z-enamides. An intramolecular amidation for the synthesis of macrocyclic ynamides

A general and efficient method for the coupling of a wide range of amides with alkynyl bromides is described here. This novel amidation reaction involves a catalytic protocol using copper(II) sulfate-pentahydrate and 1,10-phenanthroline to direct the sp-C-N bond formation, leading to a structurally diverse array of ynamides including macrocyclic ynamides via an intramolecular amidation. Given the surging interest in ynamide chemistry, this atom economical synthesis of ynamides should invoke further attention from the synthetic organic community.     

Oxoarylation of ynamides with N-aryl hydroxamic acids

Ynamides are electron-rich alkynes with unique reactivities and act as flexible building blocks in organic synthesis. Therefore, the investigation for transformation of ynamides with exceptional selectivity and efficiency is attractive and interesting. Herein, we report an oxoarylation of ynamides with N-aryl hydroxamic acids. In the presence of catalytic Cu(OTf)₂, both the terminal and internal ynamides could undergo an addition/[3,3] sigmatropic rearrangement cascade with N-aryl hydroxamic acids to achieve oxoarylation, along with providing selective entry to (ortho-amino)arylacetamides and oxindoles. Moreover, deuterium-labelling reaction and gram-scale reaction were conducted to probe the mechanism and showcase the scalability.     

Three Component syn-1,2-Arylmethylation of Internal Alkynes**

A Pd-catalyzed three-component syn-1,2-arylmethylation of internal alkynes (ynamides/yne-acetates/alkynes) is described. The readily available and bench stable coupling partners iodo-arenes, and methyl boronic acid are successfully used in this coupling strategy to access the methyl-containing tetra-substituted olefins; the scope is broad showing excellent functional-group tolerance. Notably, the transformation is regio- as well as stereoselective. The biologically relevant motifs (BRM) bearing iodo-arenes and ynamides are also used for the late-stage syn-1,2-arylmethylation of alkynes. Aryl-alkylation, aryl-trideuteriomethylation, alkynyl-methylation, and alkenyl-methylation of ynamides are also presented. The Me-substituted alkenes are further transformed into synthetically important β-amino-indenones and α-fluoro-α′-methyl ketones.     

Highly regio- and stereocontrolled synthesis of β-substituted α-tributylstannyl enamides

The regio- and stereocontrolled synthesis of β-substituted α-stannyl enamides is reported starting from internal ynamides. The synthesis of new ynamides as well as bis-ynamides is also described. Finally first examples of successful cross-coupling to afford α/β-disubstituted enamides are also reported.     

Nickel-catalyzed regio- and stereoselective hydrophosphinylation of internal ynamides with H-phosphinates

A method for the catalytic hydrophosphinylation of internal ynamides with H-phosphinates has been developed for the first time. The protocol employing the catalyst generated from NiBr₂ and PPh₃ could be applied to several types of ynamides and H-phosphinates, affording (E)-β-aminovinylphosphinates in a highly regio- and stereoselective manner.     

Diversity in Gold‐Catalyzed Formal Cycloadditions of Ynamides with Azidoalkenes or 2H‐Azirines: [3+2] versus [4+3] Cycloadditions

Gold‐catalyzed cycloadditions of ynamides with azidoalkenes or 2H‐azirines give [3+2] or [4+3] formal cycloadducts of three classes. Cycloadditions of ynamides with 2H‐azirine species afford pyrrole products with two regioselectivities when the C_β‐substituted 2H‐azirine is replaced from an alkyl (or hydrogen) with an ester group. For ynamides substituted with an electron‐rich phenyl group, their reactions with azidoalkenes proceed through novel [4+3] cycloadditions to deliver 1H‐benzo[d]azepine products instead.     

Synthesis of carbazoles by dehydro Diels-Alder reactions of ynamides

A new approach to carbazoles and benzannulated carbazoles by means of intramolecular dehydro Diels-Alder of ynamides is reported. N-(o-Ethynyl)aryl ynamides and N-(o-ethynyl) arylynamides were prepared in a few steps starting from o-iodoaniline. Thermal cycloaddition of N-(o-ethynyl)aryl ynamides and N-(o-ethynyl) arylynamides affords carbazoles and benzannulated and heteroannulated carbazoles in moderate-to-good yields.     

Gold-Catalyzed Annulations of N-Propargyl Ynamides with Anthranils with Two Distinct Chemoselectivities

Gold-catalyzed annulation of N-propargyl ynamides with anthranils can proceed by two distinct mechanisms. In the case of a terminal N-propargyl ynamide, its resulting α-imino gold carbene reacts with a tethered alkyne to generate a vinyl cation to enable hydrolysis, which ultimately yields a pyrrolo[2,3-b]quinoline derivative after treatment with p-toluenesulfonic acid. For an internal alkyne, its α-imino gold carbene reacts with a tethered alkyne via either a vinyl cation or an alkenylgold carbene; both paths ultimately lead to a 4-ketone-2-aminopyrrole derivative. Our mechanistic analysis indicates that water is a better nucleophile than anthranil for terminal ynamides, whereas water and anthranils are equally reactive for internal ynamides.     

A copper-catalyzed C-N bond formation involving sp-hybridized carbons. A direct entry to chiral ynamides via N-alkynylation of amides

A copper-catalyzed new C-N bond formation involving a sp-hybridized carbon is described here leading to a facile entry for syntheses of chiral ynamides. This direct N-alkynylation of amides should have a significant impact on the future development of synthetic methodologies employing ynamides.     

Sonogashira cross-couplings of ynamides. Syntheses of urethane- and sulfonamide-terminated conjugated phenylacetylenic systems

[reaction: see text] The first successful Sonogashira coupling of ynamides with aryl and vinyl iodides is described here. This study resolves the problem of the competing pathway involving homocoupling of ynamides and provides a practical entry to novel urethane- or sulfonamide-terminated conjugated acetylenic systems. An interesting tandem hydrohalogenation and Sonogashira coupling was also observed to give an en-ynamide.     

Au(Ⅰ)-Catalyzed Annulation of Benzofurazan N-oxides with Ynamides: From Predicting the Chemo-Selectivity to the Synthesis of 7-Nitroindole Derivatives

Summaryof main observation and conclusion It could be proposed that gold(I)-catalyzed reactions of ynamides with benzofurazan N-oxidesmightproceed through eitherO-attack or N-attack to affordα-oxo orα-imino Au(I)-carbenoidintermediates.Computational studies were performed to predict that benzofurazan N-oxides are ready to undergo the chemoselective N-attack tothe Au(I)-activatedynamides to generate theα-imino Au(I)-carbenoid intermediate.Experimental studies were carried out to confirm the computational results and the 7-nitroindole derivatives were synthesized in a concise and efficient manner.The unfavored O-attack for benzofurazan N-oxides,which is in contrast to nitrones and pyridine/quinoline N-oxides,in the Au(I)-catalyzed reactions with ynamides is rationalized.