Brønsted acid-mediated reactions of ynamides

Copper-Catalyzed and 1,3-Sulfonyl Migration Enabled Installation of Azaindoles in the Periphery of Aryl Rings: Synthesis of Sulfonylated Pyrrolo[2,3-b]quinolines and Investigation of Antimalarial Potency

Herein, an atom efficient and one-pot protocol, offering a series of sulfonylated pyrrolo[2,3-b]quinolines via C-N, C-C, and C-S bond formation, has been developed with an inexpensive copper catalyst. Notably, the reaction proceeds via a double-annulation reaction followed by a 1,3-sulfonyl migration sequence. Moreover, the method is applicable to a broad range of 2-carbonylanilines. Furthermore, synthetic applications and the scale-up reaction highlight the utility potential of this protocol. In addition, the antimalarial property of sulfonylated pyrrolo[2,3-b]quinolines showed parasite inhibition without cytotoxic effects in mammalian cells.

Synthesis of Functionalized Indolizines through 1,3-Dipolar Cycloaddition of Zwitterionic Ketenimines and Pyridinium Salts

A straightforward and efficient strategy for the synthesis of fully functionalized indolizines has been developed through a transition metal- and oxidant-free [3 + 2] cycloaddition reaction of zwitterionic ketenimines and pyridinium salts. This versatile method proceeds under mild conditions, affording functionalized indolizines in moderate to good yields. This efficient approach involves an intermolecular [3 + 2] cycloaddition, followed by enamine/imine tautomerization and aromatization. Notably, this method demonstrates broad functional group compatibility and allows for facile scalability, making it a valuable tool for the synthesis of indolizine-based frameworks in organic and medicinal chemistry.

Homogeneous Gold Catalysis: Development and Recent Advances

Gold catalysis has witnessed remarkable advances over the past decade, with numerous insightful reviews chronicling this progress. However, a comprehensive review addressing developments in the field during the post-pandemic COVID era remains notably absent. This review aims to bridge that gap by providing an in-depth analysis of recent studies, shedding light on the unique properties of gold complexes, particularly the intriguing aurophilic interactions that distinguish gold chemistry. The review systematically explores the latest achievements in both mono- and dinuclear gold-catalyzed reactions, with a focus on their applications in diverse fields, including redox coupling, asymmetric catalysis, photo-, and electrocatalysis. A special emphasis is placed on the comparative performance of mono- and dinuclear gold catalysts, with the latter often exhibiting enhanced catalytic efficiency and selectivity in certain reactions. By integrating mechanistic insights and DFT perspectives with representative experimental studies from recent years, this review highlights the significance of gold catalysis to synthetic chemistry, identifies emerging trends and outlines future directions for the field.

Nitrogen-Based Organofluorine Functional Molecules: Synthesis and Applications

Fluorine and nitrogen form a successful partnership in organic synthesis, medicinal chemistry, and material sciences. Although fluorine-nitrogen chemistry has a long and rich history, this field has received increasing interest and made remarkable progress over the past two decades, driven by recent advancements in transition metal and organocatalysis and photochemistry. This review, emphasizing contributions from 2015 to 2023, aims to update the state of the art of the synthesis and applications of nitrogen-based organofluorine functional molecules in organic synthesis and medicinal chemistry. In dedicated sections, we first focus on fluorine-containing reagents organized according to the type of fluorine-containing groups attached to nitrogen, including N-F, N-RF, N-SRF, and N-ORF. This review also covers nitrogen-linked fluorine-containing building blocks, catalysts, pharmaceuticals, and agrochemicals, underlining these components' broad applicability and growing importance in modern chemistry.

Gold-Catalyzed Intermolecular Assembly of Donor and Acceptor Fragments for [1,5]-Hydride Migrations

The [1,n]-hydride migration reactions represent one of the most powerful techniques to functionalize C(sp3)-H bonds and to rapidly construct molecular complexities. However, their substrates usually required multiple steps to prepare in advance. Herein, we developed a gold-catalyzed intermolecular coupling of hydride-donor-containing nucleophiles (amines) and hydride-acceptor-containing alkynes (1,3-diynamides) for cascade [1,5]-hydride migrations. Control experiments revealed the role of the dichloroethane solvent and the unexpected involvement of protonated anilines in promoting [1,5]-hydride migrations.

Copper-Catalyzed Triyne Cyclization via Vinyl Cations

Herein, we describe an efficient copper-catalyzed cyclization of triynes via vinyl cation intermediates. The reaction leads to the practical and atom-economical synthesis of valuable polycyclic pyrroles by constructing three new rings in one step under mild reaction conditions. The proposed reaction mechanism shows the ordered and regioselective reaction of alkynes. Moreover, the possibility of such an asymmetric triyne cyclization also emerges.

TMSOTf/TfOH-Promoted [4 + 2] Annulation of Ynamides with 2-Aminoarylnitriles To Construct 2,4-Diaminoquinolines

An effective strategy to synthesize 2,4-diaminoquinoline compounds has been efficaciously developed via a TMSOTf/TfOH-promoted [4 + 2] annulation of ynamides with 2-aminoarylnitriles. Compared with the reported transition-metal catalysts, this metal-free promotion system presented a remarkable advancement, enabling the facile and regiospecific assembly of 2,4-diaminoquinoline frameworks with wide functional group compatibility and moderate to excellent yields.

Gold-Catalyzed Synthesis of (Dihydro)quinolones by Cyclization of Benzaldehyde-Tethered Ynamides and Anilines

2-Quinolones represent a versatile class of compounds that are prevalent in natural and medicinally relevant molecules. Here we report a new approach to the selective formation of these structures. By gold catalysis, a range of benzaldehyde-tethered ynamides reacted with anilines, leading to 4-amino-3,4-dihydro-2-quinolones with high efficiency and excellent diastereoselectivity in dichloromethane. Interestingly, with methyl acetate as the solvent, the same reaction produced 3-aryl 2-quinolones as the major products. The use of a substoichiometric amount of the aniline could also promote this transformation.

Synthesis of Arenesulfenyl Fluorides and Fluorosulfenylation of Alkenes, Alkynes, and α-Diazocarbonyl Compounds

Sulfenyl fluorides are organic compounds of sulfur in formal oxidation state +2 with the formula R-S-F. Although the chloride, bromide, and iodide analogues have been extensively described in the literature, arenesulfenyl fluorides remain essentially unstudied. These structures have been implicated as putative intermediates in established processes to access polyfluorinated sulfur species; however, definitive and direct evidence of their existence has not been obtained, nor has a systematic understanding of their reactivity. Here, we report the synthesis, isolation, and spectroscopic characterization of several arenesulfenyl fluorides, including structural analysis of 2,4-dinitrobenzenesulfenyl fluoride and 4-cyano-2-nitrobenzenesulfenyl fluoride by single-crystal X-ray diffraction. The functional group undergoes direct, efficient, and highly regioselective anti-addition to alkenes and alkynes, as well as insertion by carbenes. The resulting α- or β-fluoro thioether adducts can be readily transformed into useful fluorinated motifs, for example by modification of the sulfur groups (to sulfonamides or sulfonyl fluorides), by sulfur elimination (to generate formal C-H fluorination products), or by Julia-Kocienski olefination (to form vinyl fluorides). Thus, we establish that sulfenyl fluorides are unexpectedly accessible and stable compounds, which serve as versatile reagents for the production of fluorinated organic compounds.

Regioselective N-arylation of N-Acylsulfenamides Enabled by o-Quinone Diimides

The functionalization of N-acylsulfenamides is a research focus in organosulfur chemistry, as the N-S array has unique properties and versatile applications. Although great progress has been made in S-functionalization, the N-functionalization, especially the N-arylation of N-acylsulfenamides, has rarely been explored because of the lower nucleophilicity of the N-site. Herein, we report a Brønsted acid-catalyzed regioselective N-arylation reaction of N-acylsulfenamides with o-quinone diimides. Under mild and metal-free conditions, a wide range of N-arylated N-acylsulfenamides have been prepared in good yields with excellent regioselectivity. The ease of gram-scale synthesis and transformations into useful sulfonamides demonstrates their synthetic practicality.

Isoxazoles as efficient alkyne amination reagents in divergent heterocycle synthesis

During the past decades, the exploration of new alkyne amination reactions has attracted increasing attention due to the high efficiency in heterocycle synthesis. In addition to the well-established alkyne amination reagents (such as nitrogen ylides and azides), isoxazoles and their derivatives have been proven to be efficient amination reagents, especially the N,O-bifunctional reagents of alkynes, in the transition metal-catalyzed transformation of alkynes through metal carbene intermediates. Isoxazole derivatives have been extensively applied to the rapid synthesis of a diverse range of structurally complex N-containing molecules, especially the valuable N-heterocycles in atom-economic manner. In this review, we summarize the latest trends and developments of isoxazole-enabled alkyne amination reactions and their applications in divergent heterocycle synthesis, including amination of ynamides, amination of ynol ethers, amination of thioynol ethers, amination of electron-deficient alkynes, amination of unpolarized alkynes and asymmetric amination of alkynes. Finally, we list the current challenges and opportunities for potential breakthroughs in this field.

HFIP-mediated, regio- and stereoselective hydrosulfenylation of ynamides: a versatile strategy for accessing ketene N,S-acetals

Herein, we report an HFIP-mediated, versatile, sustainable, atom-economical, and regio- and stereoselective hydro-functionalization of ynamides with various S-nucleophiles (1 equiv.) such as thiols, thiocarboxylic acids, carbamates, xanthates, and O,O-diethyl S-hydrogen phosphorothioate to access a wide variety of stereodefined trisubstituted ketene N,S-acetals under mild conditions. This protocol requires only HFIP, which plays multiple roles, such as acting as a Brønsted acid to protonate the ynamide regioselectively at the beta carbon to generate the reactive keteniminium intermediate, stabilizing the intermediate as solvent through H-bonding. After the nucleophilic attack of the S-nucleophile on the keteniminium intermediate and deprotonation, HFIP is regenerated in most of the cases and can be easily recovered and recycled, revealing the high sustainability of the protocol. Remarkably, all the reactions are highly efficient and furnish ketene N,S-acetals in excellent yields and in many cases pure products were obtained just by washing the crude reaction mixture with pentane. Significantly, the green chemistry metrics of the protocol are found to be excellent.

Copper-Catalyzed Intermolecular [2 + 2 + 2] Annulation of Diynes with Alkynes: Construction of Carbazoles

Transition-metal-catalyzed [2 + 2 + 2] annulation of alkynes is an efficient pathway for the synthesis of aromatic compounds. However, most of the established methods require noble metal catalysts. Herein, we report a copper-catalyzed intermolecular [2 + 2 + 2] annulation of diynes with alkynes through vinyl cation intermediates, enabling the atom-economical preparation of biologically important carbazole skeletons. The reaction shows good regioselectivity in the reaction of aryl(alkyl)alkynes. Moreover, preliminary results have also been obtained for the related catalytic atroposelective transformation. This reaction represents a rare example of non-noble-metal-catalyzed intermolecular [2 + 2 + 2] annulation of ynamides through the vinyl cation pathway.

Synthetic Strategy for Unsymmetrical α-Fluoro-α'-aryl Ketones

α-Fluoro-α'-aryl ketones are crucial in pharmaceuticals and agrochemicals. However, synthesizing unsymmetrical α-fluoro-α'-aryl ketones poses regioselective challenges. This study presents a one-pot aryl-oxy-fluorination method for synthesizing such unsymmetrical fluoro-aryl ketones. Using ynamide, aryl boronic acid, and F-source under Pd-catalysis, this method efficiently produces a wide range of valuable α-fluoro-α'-aryl ketones with potential applications. Through a combination of control experiments and DFT studies, we proposed a reaction mechanism involving in situ acetic acid formation.

Intermediate Control: Unlocking Hitherto Unknown Reactivity and Selectivity in N-Conjugated Allenes and Alkynes

ConspectusControlling selectivity through manipulation of reaction intermediates remains one of the most enduring challenges in organic chemistry, providing novel solutions for selective C-C π-bond functionalization. This approach, guided by activation principles, provides an effective method for selective functional group installation, enabling direct synthesis of organic molecules that are inaccessible through conventional pathways. In particular, the selective functionalization of N-conjugated allenes and alkynes has emerged as a promising research focus, driven by advances in controlling reactive intermediates and activation strategies. In this regard, our group, alongside others, has established some new approaches that have emerged as a suitable platform for the synthesis of functionalized enamides. This Account reviews recent developments in the field, highlighting new modes of reactivity and selectivity, atom-economical functionalizations, and strategies for regio- and stereocontrol, while providing mechanistic insights into related transformations.Our study is systematically organized into two sections based on substrate type and chronological research progression. In the first section, we establish a platform by controlling allenamide-derived intermediates, enabling both allenamide-alkyne (AA) cross-coupling and a few novel electrophile-promoted hydrofunctionalization reactions. The unprecedented selectivity in Pd-catalyzed allenamide-alkyne cross-coupling is achieved through neighboring group chelation, with phosphine ligand selection controlling the reaction outcome. In parallel, the electrophile-promoted functionalizations─including haloalkynylation, hydrooxycarbonylation, hydrodifluoroalkylation, and intermolecular hydroamination─are achieved through strategic selection of electrophiles or their precursors.Additionally, our findings demonstrate how ynamides' reactivity toward both electrophiles and nucleophiles, controlled through activator modulation, expands the scope of accessible transformations. Key findings include: (1) chemoselective [2 + 2 + 2] annulation through efficient trapping of N-arylated nitrilium electrophiles by ynamides, (2) divergent C-H annulation of indole-derived vinylogous ynamides controlled by metal and ligand selection via intramolecular hydroarylation, (3) bromoalkynylation-enabled functional group migration through a novel 1,3-alkynyl shift.The final section explores how N-electron polarization in 1,3-enynes enables new chemoselectivity in metal-free inter- and intramolecular couplings with indole substrates. Our findings demonstrate that modulating N-electron conjugation within the enyne skeleton─through both linear and cross conjugation─can direct activation pathways and control product selectivity.This Account aims to stimulate broader research into the intermediate-controlled functionalization of activated π-systems. Future research directions include advanced activator design, novel functional group migration strategies, and deeper mechanistic studies to enable rational reaction development.

Copper-Catalyzed [2,3]-Sigmatropic Rearrangement of Azide-Ynamides via Selenium Ylides

A copper-catalyzed [2,3]-sigmatropic rearrangement of azide-ynamides via selenium ylides is disclosed, which leads to the practical and divergent synthesis of a variety of tricyclic heterocycles bearing a quaternary carbon stereocenter in generally moderate to excellent yields. Significantly, this method represents the first [2,3]-sigmatropic rearrangement of the selenium ylide based on alkynes and an unprecedented [2,3]-sigmatropic rearrangement via α-imino copper carbenes.

Copper-Catalyzed Enantioselective Dehydro-Diels-Alder Reaction: Atom-Economical Synthesis of Axially Chiral Carbazoles

The dehydro-Diels-Alder (DDA) reaction is a powerful method for the construction of aromatic compounds. However, the enantioselective DDA reaction has been rarely developed, probably due to the competitive thermal reaction. Herein, we report a copper-catalyzed enantioselective DDA reaction through vinyl cation pathway. The reaction leads to the atom-economical synthesis of axially chiral phenyl and indolyl carbazoles in generally excellent yields with good to excellent atroposelectivities. This methodology represents the first example of non-noble metal-catalyzed enantioselective DDA reaction. Notably, new chiral ligand and organocatalyst derived from the constructed axially chiral carbazole are demonstrated to be useful in asymmetric catalysis.

Metal Additive-Free Iodine-Promoted Reorganization of Ynamide-Ynes and Stereoselective 1,2-Diiodination

We report a metal additive-free iodine-promoted one-step structural reorganization of ynamide-ynes and simultaneous stereoselective 1,2-diiodination of the migrated alkyne to form stereospecific tetrasubstituted alkenyl diiodo-tethered indoles (E-isomer). Molecular iodine is cost effective, user friendly, less toxic, commercially available, and easy to handle. The key features of the reaction include metal-and additive-free environment, selectivity, structural reorganization, mild reaction conditions, simple workup, and gram-scale synthesis. This transformation generates multiple bonds [nitrogen (N)-carbon (C)sp2, Csp2-Csp2, 2 Csp2-iodine (I)] via N-Csp bond cleavage in ynamide-ynes.

Transition-Metal-Free Radical Relay Cascade Annulation of Amides: Access to Antitumor Active Benzo[b]azepine and Oxindole Derivatives

Efficient transition-metal-free synthesis of benzo[b]azepines and oxindoles is achieved via a radical relay cascade strategy employing halogen atom transfer (XAT) for aryl radical generation followed by intramolecular hydrogen atom transfer (HAT). Optimization yielded moderate to substantial yields under visible light irradiation. Preliminary biological assessments revealed promising anti-tumor activity for select compounds. This study underscores the potential of XAT-mediated radical relay cascades in medicinal chemistry and anticancer drug discovery.

Asymmetric Büchner reaction and arene cyclopropanation via copper-catalyzed controllable cyclization of diynes

The asymmetric Büchner reaction and related arene cyclopropanations represent one type of the powerful methods for enantioselective dearomatization. However, examples of asymmetric Büchner reactions via a non-diazo approach are quite scarce, and the related arene cyclopropanation based on alkynes has not been reported. Herein, we disclose an asymmetric Büchner reaction and the related arene cyclopropanation by copper-catalyzed controllable cyclization of N-propargyl ynamides via vinyl cation intermediates, leading to chiral tricycle-fused cycloheptatrienes and benzonorcaradienes in high yields and enantioselectivities. Importantly, this protocol represents an asymmetric arene cyclopropanation reaction of alkynes and an asymmetric Büchner reaction based on vinyl cations.

Dearomative spirocyclization of ynamides

Spiro N-heterocycles, particularly aza-spiro piperidines, have shown significant promise in pharmaceutical applications due to their ability to enhance physicochemical properties. Despite their potential, the preparation of these complex structures poses significant challenges. To address this, we propose a one-pot dearomative spirocyclization reaction of ynamides. This method involves a copper-catalyzed carbomagnesiation reaction, achieving chemo-, regio-, and stereoselective formation of vinyl metal intermediates. Upon the addition of a Lewis acid, these intermediates undergo a regioselective nucleophilic dearomatization event, facilitating the synthesis of diverse aza-spiro dihydropyridine scaffolds with multiple functional handles. Various Grignard reagents, diverse ynamides, and acylating reagents have been explored. A subsequent hydrogenation reaction provides access to both partially and fully reduced spirocyclic frameworks, broadening the scope of spirocyclic structures with potential medicinal applications.

Ficini Reaction with Acrylates for the Stereoselective Synthesis of Aminocyclobutanes

The first Ficini reaction between ynamides and acrylates is reported herein. The reaction is catalyzed by B(C6F5)3 acting as a Lewis acid and is giving access to stable tri-substituted aminocyclobutenes in high yield. The resulting products can be hydrogenated and epimerized under basic conditions or in presence of a Lewis acid, providing two distinct trans- aminocyclobutane monoester stereoisomers in high yield and diastereoisomeric ratio (up to quantitative yield and >99 : 1 dr).

Asymmetric one-carbon ring expansion of diverse N-heterocycles via copper-catalyzed diyne cyclization

One-carbon ring expansion reaction of N-heterocycles has gained particular attention in the past decade because this method allows for the conversion of readily available N-heterocycles into potentially useful complex ring-expanded N-heterocycles, which are inaccessible by traditional methods. However, the catalytic asymmetric variant of this reaction has been rarely reported to date. Herein, we disclose an enantioselective one-carbon ring expansion reaction through chiral copper-catalyzed diyne cyclization, leading to the practical, atom-economic and divergent assembly of an array of valuable chiral N-heterocycles bearing a quaternary stereocenter in generally good to excellent yields with excellent enantioselectivities (up to >99% ee). This protocol represents the first example of asymmetric one-carbon ring expansion reaction of N-heterocycles based on alkynes.

TfOH-Catalyzed Reactions of Aryl Methyl Ketones with Ynamides: Synthesis of 1-Amino-1H-indenes and 2,4-Dienamides

The efficient synthesis of 1-amino-1H-indenes and 2,4-dienamides was realized via TfOH-catalyzed reactions of aryl methyl ketones with terminal ynamides in two distinct pathways. Aromatic ketones with high electrophilicity underwent [3 + 2] annulation with ynamides to produce 1-amino-1H-indenes, while aromatic ketones with low electrophilicity proceeded under the same conditions to afford 2,4-dienamides. Furthermore, the obtained 1-amino-1H-indenes could be converted into the corresponding 1H-indenes and dihydro-1H-indenes in excellent yields.

Gold-Catalyzed Alkyne Oxidative Cyclization/Mannich-Type Addition Cascade Reaction of Ynamides with 1,3,5-Triazinanes

Herein, a gold-catalyzed alkyne oxidative cyclization/Mannich-type addition cascade reaction of ynamides with 1,3,5-triazinanes in the presence of a Brønsted acid has been presented. A class of functionalized fluorenes bearing a quaternary carbon center was synthesized directly with moderate to excellent yields via in situ formed α-oxo carbenes using quinoline N-oxide as the oxidant under mild reaction conditions.

Access to Piperazine-Fused Pyrrolocarbazoles Enabled by Acid-Catalyzed Stereoselective Hydroarylation of Ynamide-Indoles and Subsequent Diels-Alder Reactions/Aromatizations

Pyrrolocarbazole skeletons are well known to possess a variety of biological activities that might be therapeutically useful in the treatment of cancers. Herein, an acid-catalyzed stereoselective hydroarylation/Diels-Alder cycloaddition/aromatization of ynamide-indoles is described. We newly designed and synthesized a variety of piperazine-fused pyrrolocarbazole derivatives that could be further applied to the synthesis of potent Wee1 inhibitors.

Lewis Acid Catalyzed Cycloaddition of Bicyclobutanes with Ynamides for the Synthesis of Polysubstituted 2-Amino-bicyclo[2.1.1]hexenes

Synthesis of bicyclic scaffolds has gained significant attention in drug discovery due to their potential to mimic benzene bioisosteres. Here, we present a mild and scalable Sc(OTf)3-catalyzed [3+2] cycloaddition of bicyclo[1.1.0]butanes (BCBs) with ynamides, yielding a diverse array of polysubstituted 2-amino-bicyclo[2.1.1]hexenes in good to excellent yields. These products offer valuable starting materials for the construction of novel functionalized bicyclo[1.1.0]butanes. Preliminary mechanistic studies indicate that the reaction involves a nucleophilic addition of ynamides to bicyclo[1.1.0]butanes, followed by an intramolecular cyclization of in situ generated enolate and keteniminium ion. We expect that these findings will encourage utilization of complex bioisosteres and foster further investigation into BCB-based cycloaddition chemistry.

Gold(I)-catalysed cyclisation of (E)-ketene-N,O-acetals: a synthetic route toward spiro-oxazole-γ-lactones

In this study, we developed a cascade 5,5-cyclisation of internal ketene-N,O-acetals utilizing homogeneous Au(I) catalysis. This process involves an initial 5-exo-dig carbocyclisation, followed by a 5-exo-dig heterocyclisation that stereoselectively incorporates the O-atom of a water molecule into an N-tethered propargyl alkyne. This sequential reaction results in the formation of one C-C, two C-O, and two C-I bonds, ultimately leading to the synthesis of spiro-α-iodo-γ-lactone structures featuring oxazole rings in good yields.

Controllable Synthesis of Cyclopenta[b]indolines via Photocatalytic Fluoroalkylative Radical Cyclization Cascade of Ynamides

A de novo method for direct construction of cyclopenta[b]indolines via a photocatalytic fluoroalkylative radical cyclization cascade of ynamides has been established, which proceeds via a sequence of radical addition, 1,5-HAT, 5-endo-trig cyclization, intramolecular arylation, and oxidative deprotonation. This protocol allows for the controllable assembly of a tricyclic architecture with three contiguous stereocenters, showcasing its high efficiency, compatibility, and regio- and diastereoselectivity for accessing pharmacologically significant fluoroalkylated cyclopenta[b]indolines. It represents one of the very few examples of tetrafunctionalization of alkynes.

Brønsted acid catalyzed Ficini [2 + 2] cycloaddition of ynamides with enones

Herein, we describe a novel metal-free Brønsted acid-catalyzed Ficini [2 + 2] cycloaddition of ynamides with enones under mild reaction conditions, leading to the formation of various cyclobutenamides in generally good to excellent yields within short reaction times. This work represents the first example of ynamides involved in a nonmetal-catalyzed [2 + 2] cycloaddition with enones.

Stereodivergent Synthesis of 1,4-Dicarbonyl Compounds through Sulfonium Rearrangement: Mechanistic Investigation, Stereocontrolled Access to γ-Lactones and γ-Lactams, and Total Synthesis of Paraconic Acids

Although simple γ-lactones and γ-lactams have received considerable attention from the synthetic community, particularly due to their relevance in biological and medicinal contexts, stereoselective synthetic approaches to more densely substituted derivatives remain scarce. The in-depth study presented herein, showcasing a straightforward method for the stereocontrolled synthesis of γ-lactones and γ-lactams, builds on and considerably expands the stereodivergent synthesis of 1,4-dicarbonyl compounds by a ynamide/vinyl sulfoxide coupling. A full mechanistic and computational study of the rearrangement was conducted, uncovering the role of all of the reaction components and providing a rationale for stereoselection. The broad applicability of the developed tools to streamlining synthesis is demonstrated by concise enantioselective total syntheses of (+)-nephrosteranic acid, (+)-rocellaric acid, and (+)-nephromopsinic acid.

Copper-Catalyzed [2 + 2] Cyclization/Ring Expansion of Ene-Ynamides: Construction of Medium- and Large-Sized Rings

Catalytic cyclization of enynes is an efficient approach for the preparation of cyclic compounds, and a large variety of four- to six-membered rings could be synthesized using this method. However, it has been rarely employed for the construction of medium- and large-sized rings. Herein, we describe a copper-catalyzed cycloisomerization of ene-ynamides through a [2 + 2] cyclization/electrocyclic ring opening cascade, leading to the atom-economical assembly of indole-fused medium- and large-sized rings in moderate to excellent yields under mild reaction conditions. Importantly, the synthetic utility of this reaction was demonstrated by the convenient synthesis of iprindole.

TMSOTf-Catalyzed [4 + 2] Annulation of Ynamides and β-(2-Aminophenyl)-α,β-ynones for the Synthesis 2-Aminoquinolines

A metal-free TMSOTf-catalyzed [4 + 2] annulation of ynamides with β-(2-aminophenyl)-α,β-ynones enables the regiospecific and facile assembly of 2-aminoquinoline frameworks. The catalyst TMSOTf presented a remarkable advancement compared to previously reported transition-metal catalysts. A wide range of 3-aryl/alkyl-substituted 2-aminoquinolines were generated in moderate to excellent yields due to the mild conditions.

Enantioselective functionalization of unactivated C(sp3)-H bonds through copper-catalyzed diyne cyclization by kinetic resolution

Site- and stereoselective C-H functionalization is highly challenging in the synthetic chemistry community. Although the chemistry of vinyl cations has been vigorously studied in C(sp3)-H functionalization reactions, the catalytic enantioselective C(sp3)-H functionalization based on vinyl cations, especially for an unactivated C(sp3)-H bond, has scarcely explored. Here, we report an asymmetric copper-catalyzed tandem diyne cyclization/unactivated C(sp3)-H insertion reaction via a kinetic resolution, affording both chiral polycyclic pyrroles and diynes with generally excellent enantioselectivities and excellent selectivity factors (up to 750). Importantly, this reaction demonstrates a metal-catalyzed enantioselective unactivated C(sp3)-H functionalization via vinyl cation and constitutes a kinetic resolution reaction based on diyne cyclization. Theoretical calculations further support the mechanism of vinyl cation-involved C(sp3)-H insertion reaction and elucidate the origin of enantioselectivity.

Acid-Catalyzed Highly Enantioselective Synthesis of α-Amino Acid Derivatives from Sulfinamides and Alkynes

An enantioselective difunctionalization of activated alkynes using chiral sulfinamide reagents is developed. It is an atom and chirality transfer process that allows for the modular synthesis of optically active α-amino acid derivatives under mild conditions. The reaction proceeds through an acid-catalyzed [2,3]-sigmatropic rearrangement mechanism with predictable stereochemistry and a broad scope.

Aromatic Amine and Chiral Phosphoric Acid Synergistic Catalyzed Cascade Reaction of Alkynylnaphthols with Aldehydes

A novel approach using aromatic amines and chiral phosphoric acids in a synergistic catalytic cascade reaction of 2-alkynylnaphthols with aldehydes has been established. This method offers a direct route to preparing flavanone analogues with excellent stereoselectivity. Mechanistic studies reveal a sequential process involving addition, elimination, cyclization, and hydrolysis in which aromatic amines and chiral phosphoric acids play key roles via imine-enamine and hydrogen bonding models.

Chemoselectivity of the CuAAC/Ring Cleavage/Cyclization Reaction between Enaminones and α-Acylketenimine

Ketenimines represent an important class of reactive species, useful synthetic intermediates, and synthons. However, in general, ketenimines preferentially undergoes nucleophilic addition reactions with hydroxyl and amino groups, and carbon functional groups remain a less studied subset of such systems. Herein, we develop a straightforward syntheses of pyridin-4(1H)-imines that is achieved by cyclization of a reacting enaminone unit with α-acylketenimine which is generated from the reactions of sulfonyl azides and terminal ynones in situ (CuAAC/Ring cleavage reaction). The cascade process preferentially starts with the nucleophilic α-C of the enaminone unit instead of an amino group, attacking the electron-deficient central carbon of ketenimine, and the chemoselectivity unconventional products pyridin-4(1H)-imines were formed by intramolecular cyclization.

Copper-catalyzed room-temperature cross-dehydrogenative coupling of secondary amides with terminal alkynes: a chemoselective synthesis of ynamides

A copper-catalyzed aerobic oxidative cross-dehydrogenative coupling reaction between secondary amides and terminal alkynes has been developed. With the aid of ligands and 3 Å molecular sieves, ynamides can be efficiently synthesized at room temperature and conveniently scaled up. A legitimate mechanism involving nitrogen-centred radicals and copper trivalent intermediates has been proposed.

CuI/DMAP-Catalyzed Oxidative Alkynylation of 7-Azaindoles: Synthetic Scope and Mechanistic Studies

An efficient and practical method for the N-alkynylation of 7-azaindoles has been established by using CuI/DMAP catalytic system at room temperature and in open air. This simple protocol has been successfully employed in the synthesis of a wide range of N-alkynylated 7-azaindoles with good yields. Also, this approach is well-suited for large-scale N-alkynylation reactions. The designed N-alkynylated 7-azaindoles were further subjected to Cu-/Ir-catalyzed alkyne-azide cycloaddition (CuAAC/IrAAC) or "click" reaction for the rapid synthesis of 1,4-/1,5 disubstituted 1,2,3-triazole decorated 7-azaindoles. A mechanistic study based on density functional theory (DFT) calculations and ultraviolet-visible (UV) spectroscopic studies revealed that the CuI and DMAP combination formed a [CuII (DMAP)2 I2 ] species, which acts as an active catalyst. The DFT method was used to assess the energetic viability of an organometallic in the C-N bond formation pathway originating from the [CuII (DMAP)2 I2 ] complex. We expect that the newly designed Cu/DMAP/alkyne system will offer valuable insights into the field of Cu-catalyzed transformations.

TMSOTf-Catalyzed Reactions of N-Arylynamides with Sulfilimines To Construct 2-Aminoindoles and α-Arylated Amidines

Here, we disclose an efficient TMSOTf-catalyzed C-H annulation of aryl-terminated N-arylynamides with sulfilimines, leading to the practical assembly of various valuable 2-aminoindoles in generally moderate to excellent yields with a broad range of functional groups, while nonaryl terminated N-arylynamides undergo TMSOTf-catalyzed aminative arylation with sulfilimines providing α-arylated amidines.

Brønsted-Acid-Catalyzed Enantioselective Desymmetrization of 1,3-Diols: Access to Chiral β-Amino Alcohol Derivatives

Herein, we describe a Brønsted-acid-catalyzed enantioselective desymmetrization of 1,3-diols with alkynes through a hydroalkoxylation/hydrolysis process. The reaction leads to the atom-economical synthesis of valuable chiral β-amino alcohols under mild reaction conditions. Further synthetic transformations based on the β-amino alcohol moiety provide divergent approaches toward chiral N-containing heterocycles.

Ir/Zn-cocatalyzed chemo- and atroposelective [2+2+2] cycloaddition for construction of C─N axially chiral indoles and pyrroles

Here, an Ir/Zn-cocatalyzed atroposelective [2+2+2] cycloaddition of 1,6-diynes and ynamines was developed, forging various functionalized C─N axially chiral indoles and pyrroles in generally good to excellent yields (up to 99%), excellent chemoselectivities, and high enantioselectivities (up to 98% enantiomeric excess) with wide substrate scope. This cocatalyzed strategy not only provided an alternative promising and reliable way for asymmetric alkyne [2+2+2] cyclotrimerization in an easy handle but also settled the issues of previous [Rh(COD)2]BF4-catalyzed system on the construction of C─N axial chirality such as complex operations, limited substrate scope, and low efficiency. In addition, control experiments and theoretical calculations disclosed that Zn(OTf)2 markedly reduced the barrier of migration insertion to significantly increase reaction efficiency, which was distinctly different from previous work on the Lewis acid for improving reaction yield through accelerating oxidative addition and reductive elimination.

Chiral Auxiliary Approach for Gold(I)-Catalyzed Cyclizations

Two different classes of stereoselective cyclizations have been developed using a chiral auxiliary approach with commercially available [JohnPhosAu(MeCN)SbF6 ] as catalyst. First, a stereoselective cascade cyclization of 1,5-enynes was achieved using the Oppolzer camphorsultam as chiral auxiliary. In this case, a one-pot cyclization-hydrolysis sequence was developed to directly afford enantioenriched spirocyclic ketones. Then, the stereoselective alkoxycyclization of 1,6-enynes was mediated by an Evans-type oxazolidinone. A reduction-hydrolysis sequence was selected to remove the auxiliary to give enantioenriched β-tetralones. DFT studies confirmed that the steric clash between the chiral auxiliary and alkene accounts for the experimentally observed diastereoselective cyclization through the Si face.

Copper-catalyzed atroposelective formal [4+1] annulation of 1,2-diketones with vinyl cations

The enantioselective transformation of easily accessible 1,2-diketones represents a quick pathway towards enantioenriched molecules. Herein, we disclose a copper-catalyzed atroposelective formal [4+1] annulation of 1,2-diketones with vinyl cations, enabling the efficient and atom-economical construction of axially chiral arylpyrroles bearing 1,3-dioxole moieties with good to excellent enantioselectivities under mild reaction conditions. Importantly, this methodology constitutes the first enantioselective formal [4+1] annulation of 1,2-diketones.

Copper-catalyzed intermolecular formal (5 + 1) annulation of 1,5-diynes with 1,2,5-oxadiazoles

One-carbon homologation reactions based on one-carbon insertion into the N-O bond of heterocycles have received tremendous interest over the past decades. However, these protocols have to rely on the use of hazardous and not easily accessible diazo compounds as precursors, and examples of the relevant asymmetric catalysis have not been reported. Here we show that a copper-catalyzed intermolecular formal (5 + 1) annulation of 1,5-diynes with 1,2,5-oxadiazoles involving one-carbon insertion into the heterocyclic N-O bond via non-diazo approach. This method enables practical and atom-economic synthesis of valuable pyrrole-substituted oxadiazines in generally moderate to good yields under mild reaction conditions. In addition, the possibility of such an asymmetric formal (5 + 1) annulation also emerges.

Asymmetric Hydrative Aldol Reaction (HAR) via Vinyl-Gold Promoted Intermolecular Ynamide Addition to Aldehydes

Herein, we reported an intermolecular asymmetric hydrative aldol reaction through vinyl-gold intermediate under ambient conditions. This tandem alkyne hydration and sequential nucleophilic addition afforded a "base-free" approach to β-hydroxy amides with high efficiency (up to 95 % yields, >50 examples). Vinyl gold intermediate was applied as reactive nucleophile and Fe(acac)3 was used as the critical co-catalyst to prevent undesired protodeauration, allowing this transformation to proceed under mild conditions with good functional group tolerance and excellent stereoselectivity (>20 : 1 d.r. and up to 99 % ee).

Organocatalytic intramolecular (4 + 2) annulation of enals with ynamides: atroposelective synthesis of axially chiral 7-aryl indolines

Catalytic enantioselective transformation of alkynes has become a powerful tool for the synthesis of axially chiral molecules. Most of these atroposelective reactions of alkynes rely on transition-metal catalysis, and the organocatalytic approaches are largely limited to special alkynes which act as the precursors of Michael acceptors. Herein, we disclose an organocatalytic atroposelective intramolecular (4 + 2) annulation of enals with ynamides. This method allows the efficient and highly atom-economical preparation of various axially chiral 7-aryl indolines in generally moderate to good yields with good to excellent enantioselectivities. Computational studies were carried out to elucidate the origins of regioselectivity and enantioselectivity. Furthermore, a chiral phosphine ligand derived from the synthesized axially chiral 7-aryl indoline was proven to be potentially applicable to asymmetric catalysis.

1,3-Butadiynamides the Ethynylogous Ynamides: Synthesis, Properties and Applications in Heterocyclic Chemistry

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.

Atom-economic and stereoselective catalytic synthesis of fully substituted enol esters/carbonates of amides in acyclic systems enabled by boron Lewis acid catalysis

Carboacyloxylation of internal alkynes is emerging as a powerful and straightforward strategy for enol ester synthesis. However, the reported examples come with limitations, including the utilization of noble metal catalysts, the control of regio- and Z/E selectivity, and an application in the synthesis of enol carbonates. Herein, a boron Lewis acid-catalyzed intermolecular carboacyloxylation of ynamides with esters to access fully substituted acyclic enol esters in high yield with generally high Z/E selectivity (up to >96 : 4) is reported. Most importantly, readily available allylic carbonates are also compatible with this difunctionalization reaction, representing an atom-economic, catalytic and stereoselective protocol for the construction of acyclic β,β-disubstituted enol carbonates of amides for the first time. The application of the carboacyloxylation products to decarboxylative allylations provided a ready access to enantioenriched α-quaternary amides. Moreover, experimental studies and theoretical calculations were performed to illustrate the reaction mechanism and rationalize the stereochemistry.

Modular enantioselective access to β-amino amides by Brønsted acid-catalysed multicomponent reactions

β-Amino acids are structural motifs widely found in therapeutic natural products, novel biomimetic polymers and peptidomimetics. As a convergent method, the synthesis of stereoenriched β-amino amides through the asymmetric Mannich reaction requires specialized amide substrates or a metal catalyst for enolate formation. By a redesign of the Ugi reaction, a conceptually different solution to prepare chiral β-amino amides was established using ambiphilic ynamides as two-carbon synthons. The modulation of ynamides or oxygen nucleophiles concisely furnished three classes of β-amino amides with generally good efficiency as well as excellent chemo- and stereo-control. The utility is verified in the preparation of over 100 desired products that bear one or two contiguous carbon stereocentres, including those that directly incorporate drug molecules. This advance also provides a synthetic shortcut to other valuable structures. The amino amides could be elaborated into β-amino acids, anti-vicinal diamines, γ-amino alcohols and β-lactams or undergo transamidation with amino acids and amine-containing pharmaceuticals.