Application of Ynamides in the Synthesis of 2-Amidoindoles

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.

Recyclable gold(I)-catalyzed heterocyclization of ynamides with benzyl or indolyl azides towards 2-aminoindoles or 3-amino-β-carbolines

A highly efficient heterogeneous gold(I)-catalyzed heterocyclization of ynamides with benzyl or indolyl azides has been achieved in 1,2-dichloroethane under mild conditions via a heterogenized α-imino gold carbene intermediate using 5 mol% of SBA-15-anchored strongly hindered NHC-gold(I) complex [IPr-SBA-15-AuNTf2] as the catalyst, delivering a wide range of valuable 2-aminoindoles or 3-amino-β-carbolines in mostly good to excellent yields with high regioselectivity. Furthermore, the new heterogenized NHC-gold(I) complex displays the same catalytic activity as IPrAuNTf2 and is facile to recover by centrifugation of the reaction mixture and can be reused at least seven times without any appreciable drop in its catalytic activity.

Synthesis of Axially Chiral N-Arylindoles via Atroposelective Cyclization of Ynamides Catalyzed by Chiral Brønsted Acids

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.

Palladium-catalyzed nucleomethylation of alkynes for synthesis of methylated heteroaromatic compounds

Herein, we disclosed a novel and efficient palladium-catalyzed nucleomethylation of alkynes for the simultaneous construction of the heteroaromatic ring and methyl group. The 3-methylindoles, 3-methylbenzofurans and 4-methylisoquinolines were obtained in moderate to excellent yields. Notably, this methodology was employed as a key step for synthesis of a pregnane X receptor antagonist, zindoxifene, bazedoxifene and AFN-1252. The kinetic studies revealed that reductive elimination might be the rate-determining step.

A novel palladium-catalyzed nucleomethylation of alkynes is developed, affording 3-methylindoles, 3-methylbenzofurans and 4-methylisoquinolines in moderate to excellent yields.

2-Imidazolidinone benzofurans as unexpected outcome of the Lewis acid mediated Nenitzescu reaction

Herein, a metal-free methodology towards 2-imidazolidinone benzofurans via piperazinone enaminoesters addition onto quinones and subsequent rearrangement has been disclosed.

Lewis acid-promoted cyclizations of o-alkyloxyphenyl-substituted ynamides to construct 2-amidobenzofurans

Lewis acid-promoted cyclizations of o-alkyloxyphenyl-substituted ynamides are described for the general construction of medicinally relevant 2-amidobenzofurans. A diverse array of 3-acyl-2-amidobenzofurans could be effectively constructed via a SnCl4-promoted intermolecular cyclization....

Media-Driven Pd-Catalyzed Reaction Cascades with 1,3-Diynamides Leading Selectively to Either Indoles or Quinolines

Divergent Pd-catalyzed reaction cascades with various 1,3-diynamides yielding either 2-amino-3-alkynylindoles or 2-amino-4-alkenylquinolines were established. Omitting or adding TBAF (tetrabutylammonium fluoride) to the reaction of N,N-(2-iodophenyl)(4-toluenesulfonyl)-1,3-diynamides with secondary or primary amines in the presence of KOH in THF and catalytic amounts of Pd(PPh₃ )₄ completely changed the outcome of the reaction. In the absence of TBAF, 2-amino-3-alkynylindoles were the sole products, while the presence of TBAF switched the product formation to 2-amino-4-alkenylquinolines. Deuterium labeling proceeded selectively at the C3 and C11 positions of the 2-amino-4-alkenylquinoline products and this suggests the unprecedented formation of [4]cumulenimines from 1,3-diynamides as reactive key intermediates.

Synthesis of Indoles via Intermolecular and Intramolecular Cyclization by Using Palladium-Based Catalysts

As part of natural products or biologically active compounds, the synthesis of nitrogen-containing heterocycles is becoming incredibly valuable. Palladium is a transition metal that is widely utilized as a catalyst to facilitate carbon-carbon and carbon-heteroatom coupling; it is used in the synthesis of various heterocycles. This review includes the twelve years of successful indole synthesis using various palladium catalysts to establish carbon-carbon or carbon-nitrogen coupling, as well as the conditions that have been optimized.

Metal-Free [3+2] Annulation of Ynamides with Anthranils to Construct 2-Aminoindoles

A novel metal-free [3+2] annulation of ynamides with anthranils provides a facile, flexible, environmentally friendly, and atom-economical route to 2-aminoindoles. This synthetic process proceeds with efficiency, excellent regioselectivity, and wide functional group tolerance under mild conditions. Moreover, the obtained 2-aminoindole products represent a multifunctional platform for the construction of various 2-aminoindolyl frameworks.

Reactivity of ynamides in catalytic intermolecular annulations

Ynamides are unique alkynes with a carbon-carbon triple bond directly attached to the nitrogen atom bearing an electron-withdrawing group. The alkyne is strongly polarized by the electron-donating nitrogen atom, but its high reactivity can be finely tempered by the electron-withdrawing group. Accordingly, ynamides are endowed with both nucleophilic and electrophilic properties and their chemistry has been an active research field. The catalytic intermolecular annulations of ynamides, featuring divergent assembly of structurally important amino-heterocycles in a regioselective manner, have gained much attention over the past decade. This review aims to provide a comprehensive summary of the advances achieved in this area involving transition metal and acid catalysis. Moreover, the intermolecular annulations of ynamide analogs including ynol ethers and thioalkynes are also discussed, which can provide insights into the reactivity difference caused by the heteroatoms.

Di-tert-butyl Ethynylimidodicarbonate as a General Synthon for the β-Aminoethylation of Organic Electrophiles: Application to the Formal Synthesis of Pyrrolidinoindoline Alkaloids (±)-CPC-1 and (±)-Alline

The reagent di-tert-butyl ethynylimidodicarbonate is demonstrated as a β-aminoethyl anion synthetic equivalent. It can be used to install ethyleneamine groups by exploiting its terminal alkyne reactivity with common organic electrophiles. Reactions exemplified with this terminal ynimide reagent include additions to imines, aldehydes, ketones, pyridinium salts, Michael acceptors, epoxides, and Pd-catalyzed Sonogashira couplings. Subsequent regioselective [3 + 2] cycloadditions of the alkynyl-imides (ynimides) generate N,N-di-Boc imide-functionalized triazole and isoxazole heterocycles. Reduction of the ynimides with Pd-catalyzed hydrogenation generates ethyleneimides with easily removable N,N-di-Boc-carbamate protecting groups, allowing for a flexible ynimide-based approach to ethyleneamine installation. The utility of this two-step aminoethylation strategy was demonstrated in the short formal syntheses of pyrrolidinoindoline alkaloids (±)-CPC-1 and (±)-alline. Analogously, the reagent (N,N,N')-tri-Boc 2-ethynylhydrazine serves as a β-hydrazinoethyl anion synthetic equivalent.

Recent advances in the synthesis of indoles from alkynes and nitrogen sources

This review highlights ten years of success in the synthesis of indoles using alkynes and nitrogen sources as substrates.

Facile one-pot synthesis of 2-aminoindoles from simple anilines and ynamides

A highly effective and facile one-pot reaction has been developed for the synthesis of 2-aminoindoles directly from anilines and ynamides.

Reactivity of epoxy-ynamides with metal halides: nucleophile (Br/Cl/OH)-assisted tandem intramolecular 5-exo-digor 6-endo-digcyclisation and AgF2-promoted oxidation

Several metal halides (CuBr, LiCl, CuF₂, AgF₂) react with epoxy-ynamides to afford 1,3-oxazolidines, 1,4-oxazines or 1,2-dioxo-enamides.

Aerobic oxidative alkynylation of H-phosphonates and amides: an efficient route for the synthesis of alkynylphosphonates and ynamides using a recyclable Cu–MnO catalyst

We developed a straightforward, atom-economical and scalable route for the synthesis of alkynylphosphonates and ynamides using a reusable Cu–MnO catalyst.

Copper Catalyzed Intramolecular N-Arylation of Ketene Aminals at Room Temperature: Synthesis of 2-Amino-3-cyanoindoles

Various 2-amino-3-cyanoindoles are synthesized through copper catalyzed intramolecular N-arylations of ketene aminals at room temperature for the first time with 60-99% yields within 0.1-2 h. Controlled regioselective N-arylations of unsymmetrical ketene aminals are also studied. Further, a new double heteroannulation approach is demonstrated for the synthesis of 11-aminoindolo[2,3- b]quinolines from acyclic and nonheterocyclic precursors.

One-pot synthesis of propynoates and propynenitriles

An efficient transformation towards propynoates and propynenitriles is herein described. The practical methodology was conducted at low temperature (–78 or –60 °C) in a one-pot manner with the assistance of base rather than any transition metal catalysts. The base-induced protocol exhibits good functional group tolerance (up to 28 examples) and high efficiency (up to 92% yields) towards substituted acetylenes of great synthetic significance, which was also well demonstrated by the gram-scale reactions.

Gold-Catalyzed Stereoselective Synthesis of Bicyclic Lactams and Ketones from N-Tosylynamidomethyl-Tethered Cyclohexenes

Six-membered ring 3-enynamides underwent cycloisomerization in the presence of a catalytic amount of a gold(I) complex delivering mainly 4-azatricyclo[4.3.1.0^3,10]dec-2-ene derivatives and dibenz[cd,f]indole derivatives as the minor products under mild reaction conditions. Upon exposure to air, most aryl-substituted azatricycles led to bicyclic γ-lactams, while the ortho-tolyl- or alkyl-substituted azatricycles provided the corresponding bicyclic γ-lactams after oxidation with osmium tetraoxide and N-methylmorpholine-N-oxide. Under acidic conditions, the ortho-tolyl- or alkyl-substituted azatricycles were further transformed into 5-N-tosylaminomethyl-tethered bicyclo[4.2.0]octan-7-ones. The gold(I)-catalyzed tandem cycloisomerization/oxidation reaction also provided a new route for the synthesis of bridged bicyclic δ-lactams from six-membered ring 4-enynamides. The mild reaction conditions allowed the synthesis of a range of bicyclic γ- and δ-lactams and N-tosylaminomethyl-tethered bicyclo[4.2.0]octan-7-ones with high diastereoselectivities.

Synthesis of 3-Substituted 2-Aminochromones via Sn(IV)-Promoted Annulation of Ynamides with 2-Methoxyaroyl Chlorides

A Sn(IV)-promoted annulation reaction of ynamides is described for the efficient synthesis of 3-substituted 2-aminochromones under mild conditions. This novel method allows for a concomitant construction of C-C and C-O bonds between ynamides and 2-methoxyaroyl chlorides by a tandem Friedel-Crafts acylation/oxo-Michael addition/elimination strategy.

Stereoselective Synthesis of (2Z)-2,4-Dienamides via NBS-Mediated Allyloxyl Addition-Claisen Rearrangement-Dehydrobromination Cascade Reaction of Ynsulfonamides

An NBS-promoted allyloxyl addition-Claisen rearrangement-dehydrobromination cascade reaction has been developed. More than 20 substituted alkynylsulfonamides were reacted with allyl alcohols to generate (2Z)-2,4-dienamides in moderate to high yields. A mechanistic model has been proposed to account for the overall reaction sequence including the stereochemical outcome. Theoretical calculations suggested that a [3,3] sigmatropic rearrangement be the rate-limiting step.

S3S63 Terminal Ynamides: Synthesis, Coupling Reactions and Additions to Common Electrophiles

Ynamides consist of a polarized triple bond that is directly attached to a nitrogen atom carrying a sulfonyl, an alkoxycarbonyl, an acyl or another electron withdrawing group. The triple bond polarization renders ynamides broadly useful building blocks with synthetic opportunities that go far beyond traditional alkyne chemistry. The versatile reactivity of ynamides in cycloadditions, cycloisomerizations, regioselective additions with various nucleophiles or electrophiles, ring-closing metathesis, and many other reactions has been investigated in detail during the past decades. A common feature of these methods is that the triple bond is consumed and either cleaved or transformed to a new functionality. The wealth of reports on these ynamide reactions is in stark contrast to the dearth of carbon-carbon bond formations that leave the triple bond of terminal ynamides intact. The recent introduction of effective synthetic methods for the preparation of terminal ynamides has set the stage to fully explore the synthetic potential of this intriguing class of compounds. This digest letter summarizes the most effective routes to terminal ynamides and the current state of selective nucleophilic addition, substitution and coupling reactions, including the first examples of asymmetric synthesis.

1,2-N-migration in a gold-catalysed synthesis of functionalised indenes by the 1,1-carboalkoxylation of ynamides

Unique α-hemiaminal ether gold carbene intermediates were accessed by a gold-catalysed 1,1-carboalkoxylation strategy and evolved through a highly selective 1,2-N-migration. This skeletal rearrangement gave functionalised indenes, and isotopic labelling confirmed the rare C–N bond cleavage of the ynamide moiety. The effect of substituents on the migration has been explored, and a model is proposed to rationalise the observed selectivity.

Copper(I)-catalyzed nucleophilic addition of ynamides to acyl chlorides and activated N-heterocycles

The addition of ynamides to acyl chlorides and N-heterocycles activated in situ with ethyl chloroformate has been accomplished at room temperature using copper iodide as catalyst. This economical and practical carbon–carbon bond formation provides convenient access to a variety of 3-aminoynones from aliphatic and aromatic acyl chlorides in up to 99% yield. The addition to pyridines and quinolines occurs under almost identical conditions and proceeds with good to high regioselectivity, producing the corresponding 1,2-dihydro-N-heterocycles in up to 95% yield.

Catalytic enantioselective nucleophilic addition of ynamides to aldehydes

The first catalytic asymmetric addition of ynamides to aliphatic and aromatic aldehydes is described. This reaction provides unprecedented access to a diverse family of N-substituted propargylic alcohols that are obtained in high yield and ee in the presence of 10 mol% of zinc triflate and N-methylephedrine. The use of apolar solvent mixtures is essential to avoid product racemization and to optimize ee's without compromising conversion.