Alkyne Source Research Articles

Selective N‐Monovinylation of Primary Aromatic Amides Using Calcium Carbide as an Alkyne Source

AbstractAn efficient method for the selective N‐monovinylation of primary aromatic amides using calcium carbide as an alkyne source is described. A series of N‐vinylbenzamides (enamides) were readily synthesized by this strategy. The salient features for this protocol are the use of inexpensive, easy‐to‐handle solid alkyne source, high chemoselectivity, transition metal catalyst‐free, good functional group tolerance, and simple work‐up procedures. These reactions can also be extended to the gram‐scale level.

Calcium Carbide as a Surrogate of Acetylene: Copper‐Catalyzed Construction of 3‐Methylene‐2‐arylisoindolin‐1‐ones

AbstractAn efficient method for the synthesis of 3‐methylene‐2‐arylisoindolin‐1‐ones through Sonogashira cross‐coupling/nucleophilic addition tandem reactions using calcium carbide as an alkyne source, 2‐bromo‐N‐arylbenzamides as starting materials and copper as a catalyst is described. The significant advantages of this strategy include the use of cheap and easy‐to‐handle solid alkyne source as a surrogate of inflammable and explosive gaseous acetylene, inexpensive catalyst, wide scope of substrates, simple manipulations, and simple work‐up procedures.

One-Pot Synthesis of 3-Methyl-2-arylimidazo[1,2-a]pyridines Using Calcium Carbide as an Alkyne Source.

An efficient method for the construction of 3-methyl-2-arylimidazo[1,2-a]pyridines from the reactions of calcium carbide, 2-aminopyridines, and aromatic aldehydes is described. The notable advantages for this strategy include the use of an inexpensive and concise solid alkyne source, cheap and readily available raw materials, wide-scope substrates, and a simple work-up procedure.

Copper-Catalyzed Construction of Benzo[4,5]imidazo[2,1-a]isoquinolines Using Calcium Carbide as a Solid Alkyne Source.

A method for the synthesis of benzo[4,5]imidazo[2,1-a]isoquinolines through Sonogashira cross-coupling/nucleophilic addition tandem reactions using calcium carbide as a solid alkyne source, 2-(2-bromophenyl)benzimidazoles as starting materials, and copper as a catalyst is described. The target products can also be synthesized through one-pot three-component reactions of o-phenylenediamines, o-bromobenzaldehydes, and calcium carbide. Both reaction routes can also be scaled up to gram scale.

One‐Pot Three‐Component Synthesis of 2‐Methyl‐3‐aminobenzofurans Using Calcium Carbide as a Concise Solid Alkyne Source

Main observation and conclusionA one‐pot three‐component method for the synthesis of 2‐methyl‐3‐aminobenzofurans using calcium carbide as a concise solid alkyne source, and salicylaldehydes and secondary amines as starting materials is described. This protocol has salient feature of the use of inexpensive, abundant and easy‐to‐handle alkyne source, avoiding the use of inflammable and explosive acetylene gas as an original alkyne source. In addition, step economy, satisfactory yield, and simple work‐up procedure are also advantages of this route.

Direct Synthesis of 3-Coumaranones with Calcium Carbide as an Acetylene Source.

A novel synthesis method for the construction of 3-coumaranones from the reaction of two molecules, calcium carbide and salicylaldehyde, was reported. Various 2-methyl-2-vinylbenzofuran-3(2H)-ones could be obtained in moderate yields in the absence of a metal catalyst. The salient features of this protocol involve widely available starting materials, an inexpensive and easy-to-handle alkyne source, and a cost-efficient route. The reaction mechanism was verified by density functional theory calculations of possible intermediates and corresponding transition states.

Synthesis of Diarylethynes from Aryldiazonium Salts by Using Calcium Carbide as an Alkyne Source in a Deep Eutectic Solvent

AbstractAn efficient method for the synthesis of diarylethynes from aryldiazonium salts by using calcium carbide as an alkyne source at room temperature in a deep eutectic solvent is described. The salient features of this protocol are an inexpensive and easy-to-handle alkyne source, a nonvolatile and recyclable solvent, mild conditions, and a simple workup procedure.

Synthesis of 1,3‐Diynes Using Calcium Carbide as an Alkyne Source

AbstractA simple method for the synthesis of 1,3‐diynes from iodoarenes using calcium carbide as an alkyne source and air as an oxidant is described. A series of 1,4‐diarylbuta‐1,3‐diynes were efficiently synthesized by this strategy. The salient features of this protocol are the use of inexpensive and easy‐to‐handle alkyne source, broad substrate scope, open‐air condition, and simple operation procedure.

Propargyl alcohols as alkyne sources: Synthesis of heterocyclic compounds under microwave irradiation

Fused heterocyclic compounds with alkyne substituent, have been achieved using a domino microwave-assisted [Pd]-catalysis. Interestingly, tert-propargyl alcohols underwent a selective degradative β-carbon cleavage and served as masked alkynyl equivalents, in water as the sole reaction medium. Dihydrobenzofurans, indolines, and oxindoles have been accomplished using this dual C–C bond-forming strategy.

Direct Synthesis of Propen-2-yl Sulfones through Cascade Reactions Using Calcium Carbide as an Alkyne Source.

A simple method for the construction of propen-2-yl sulfones through cascade reactions of calcium carbide with arylsulfonylhydrazones using copper as a mediator is described. The salient features of this protocol are the use of readily available and easy-to-handle alkyne source, broad substrate scope, open-air condition, and simple operation procedure.

AIBN-Induced Remote Trifluoromethyl-Alkynylation of Thioalkynes.

A novel α,α'-azobis(isobutyronitrile) (AIBN)-induced remote trifluoromethyl-alkynylation of thioalkynes with alkynyl triflones as both the trifluoromethyl and alkyne sources is described. Structurally diverse trifluoromethylated (Z)-enynes can be constructed with full control of regio-, stereo-, and site-selectivity, which serves as a highly selective method for the rapid construction of trifluoromethylated molecules.

Metal‐Free Decarboxylative A3‐Coupling/Pictet–Spengler Cascade Accessing Polycyclic Scaffolds: Propiolic Acids Exceed Alkynes

Herein, we describe the development of a metal‐free decarboxylative A3‐coupling and Pictet–Spengler cascade process to directly generate functionalized tetrahydroisoquinolines from a 2‐phenylethanamine, formaldehyde, and a propiolic acid. The key feature of this efficient reactivity is the utilization of a propiolic acid as the alkyne source, with TFA as promoter. This transformation was also demonstrated to be amenable to the construction of N‐propargyl thienotetrahydropyridine and benzodiazepine skeletons under mild conditions.

Synthesis of Ferrocenyl Alkyne–Cu(I) π-Complexes via Copper-Promoted 8-Aminoquinoline-Directed C–H Bond Alkynylations

A highly monoselective synthesis of ferrocenyl alkynes was achieved via Cu-promoted ferrocene C(sp2)–H bond activations. The reaction employs an 8-aminoquinoline group as the directing group and terminal alkynes as the alkyne source. It was found the alkynylation products actually complex with the in situ generated Cu(I) ions to give robust and stable alkyne π-copper complexes. In addition, these alkyne π-copper complexes could be freed of the copper ions to give various ferrocenyl alkynes in almost quantitative yields. The test results also showed that the alkyne π-copper complexes could be reformed from the free alkynes upon treating them with Cu(I) salts.

Alkynylation of radicals: spotlight on the "Third Way" to transfer triple bonds.

The alkynylation of radical intermediates has been known since a long time, but had not been broadly applied in synthetic chemistry, in contrast to the alkynylation of either electrophiles or nucleophiles. In the last decade however, it has been intensively investigated leading to new disconnections to introduce versatile triple bonds into organic compounds. Nowadays, such processes are important alternatives to classical nucleophilic and electrophilic alkynylations. Efficient alkyne transfer reagents, in particular arylsulfones and hypervalent iodine reagents were introduced. Direct alkynylation, as well as cascade reactions, were subsequently developed. If relatively harsh conditions were required in the past, a new era began with progress in photoredox and transition metal catalysis. Starting from various radical precursors, alkynylations under very mild reaction conditions were rapidly discovered. This review covers the evolution of radical alkynylation, from its emergence to its current intensive stage of development. It will focus in particular on improvements for the generation of radicals and on the extension of the scope of radical precursors and alkyne sources.

Gold(i)- and rhodium(iii)-catalyzed formal regiodivergent C–H alkynylation of 1-arylpyrazolones

Formal regiodivergent C-H alkynylation of 1-aryl-5-pyrazolones has been realized under the catalysis of Rh(iii) and Au(i) complexes by using a hypervalent iodine reagent as the alkyne source. Mechanistic studies indicate that the regioselectivity is ascribed to not only the choice of the catalyst but also the nature of the substrate. The substrate scope and functional group compatibility have been fully examined.

Decarboxylative Alkynylation

AbstractThe development of a new decarboxylative cross‐coupling method that affords terminal and substituted alkynes from various carboxylic acids is described using both nickel‐ and iron‐based catalysts. The use of N‐hydroxytetrachlorophthalimide (TCNHPI) esters is crucial to the success of the transformation, and the reaction is amenable to in situ carboxylic acid activation. Additionally, an inexpensive, commercially available alkyne source is employed in this formal homologation process that serves as a surrogate for other well‐established alkyne syntheses. The reaction is operationally simple and broad in scope while providing succinct and scalable avenues to previously reported synthetic intermediates.

Decarboxylative Alkynylation.

The development of a new decarboxylative cross-coupling method that affords terminal and substituted alkynes from various carboxylic acids is described using both nickel- and iron-based catalysts. The use of N-hydroxytetrachlorophthalimide (TCNHPI) esters is crucial to the success of the transformation, and the reaction is amenable to in situ carboxylic acid activation. Additionally, an inexpensive, commercially available alkyne source is employed in this formal homologation process that serves as a surrogate for other well-established alkyne syntheses. The reaction is operationally simple and broad in scope while providing succinct and scalable avenues to previously reported synthetic intermediates.

Cu(I)-catalyzed one-pot decarboxylation-alkynylation reactions on 1,2,3,4-tetrahydroisoquinolines and one-pot synthesis of triazolyl-1,2,3,4-tetrahydroisoquinolines

A facile and efficient method to introduce alkyne groups to the C-1 position of biologically interesting 1,2,3,4-tetrahydroisoquinolines via direct CH-functionalization is reported. Various alkynylated N-substituted 1,2,3,4-tetrahydroisoquinolines could be obtained by using copper(I)-chloride as catalyst, alkynoic acids as alkyne source and t-BuOOH as oxidant, in a one-pot two-step decarboxylation- alkynylation reaction in moderate to high yields. Furthermore, a one-pot protocol of a three-step decarboxylation-alkynylation-1,3-dipolar cycloaddition reaction leading to 1-triazolyl-tetrahydroisoquinolines was developed, a hitherto unknown reaction cascade.

Palladium-catalyzed oxidative deacetonative coupling of 4-aryl-2-methyl-3-butyn-2-ols with H-phosphonates.

An efficient and generally applicable protocol for palladium-catalyzed oxidative deacetonative coupling of 4-aryl-2-methyl-3-butyn-2-ols with dialkyl H-phosphonates has been developed. This methodology provides a new and practical route to alkynylphosphonates using the inexpensive 4-aryl-2-methyl-3-butyn-2-ols as the alkyne sources. This reaction could also be performed with aryl bromides, 2-methyl-3-butyne-2-ol and dialkyl H-phosphonates using the cheap 2-methyl-3-butyne-2-ol as an alkyne source.

Alkynyliodonium Salt Mediated Alkynylation of Azlactones: Fast Access to Cα-Tetrasubstituted α-Amino Acid Derivatives

An efficient electrophilic alkynylation of azlactones (oxazol-5(4H)-ones) is developed using alkynyl(phenyl)iodonium salts as the electrophilic alkyne source. After remarkably short reaction times, the desired alkyne functionalized azlactones are obtained in 60-97% yield and can be transformed easily into a variety of quaternary α-amino acid derivatives.