Copper‐Catalyzed Aerobic Oxidative Transformation of Ketone‐Derived N‐Tosyl Hydrazones: An Entry to Alkynes

A novel strategy involving Cu‐catalyzed oxidative transformation of ketone‐derived hydrazone moiety to various synthetic valuable internal alkynes and diynes has been developed. This method features inexpensive metal catalyst, green oxidant, good functional group tolerance, high regioselectivity and readily available starting materials. Oxidative deprotonation reactions were carried out to form internal alkynes and symmetrical diynes. Cross‐coupling reactions of hydrazones with halides and terminal alkynes were performed to afford functionalized alkynes and unsymmetrical conjugated diynes. A mechanism proceeding through a Cu‐carbene intermediate is proposed for the C? C triple bond formation.     

Retracted: A Facile Synthetic Route to New Fluorinated Building‐Blocks of 1‐Fluoroalkynes and 1‐Fluorodiynes

A facile and direct fluorination process of alkynes and diynes was developed. In the presence of n‐butyllithium, the reaction of a series of terminal alkynes and diynes with the electrophilic fluorinating reagent (NFSI) proceeded to afford various 1‐fluoroalkynes and 1‐fluoro‐1,3‐diynes in moderate to high yields.     

Magnetic copper ferrite catalyzed homo‐ and cross‐coupling reaction of terminal alkynes under ambient atmosphere

The application of non‐toxic and magnetically separable nano‐CuFe₂O₄ as an efficient catalyst for oxidative homo‐ and cross‐coupling reaction of terminal alkynes is described. A wide range of symmetrical and unsymmetrical 1,3‐diynes have been synthesized in moderate to good yields under ambient atmosphere. The nano CuFe₂O₄ can be recovered with a magnet and reused at least five consecutive cycles with no appreciable loss of its catalytic activity.     

CuI‐catalyzed homocoupling of terminal alkynes to 1,3‐diynes

A simple and efficient protocol for CuI‐catalyzed oxidative homocoupling reaction of terminal alkynes to symmetrical 1,4‐disubstituted 1,3‐diynes was reported. The reaction can be carried out in the open air, using NaOAc as a base in the absence of any other additives. A variety of terminal alkynes were converted to the corresponding 1.3‐diynes in good to excellent yields without any side product formation. Copyright © 2010 John Wiley & Sons, Ltd.     

3‐(Diphenylphosphino)propanoic acid: an efficient ligand for the Pd/Cu‐catalyzed homo‐coupling of terminal alkynes in the presence of oxygen at room temperature

A simple, yet efficient system for PdCl₂/CuI to catalyze the homo‐coupling reactions of various terminal alkynes has been developed using 3‐(diphenylphosphino)propanoic acid as ligand in the presence of oxygen. The alkynes, including aromatic, heteroaromatic and aliphatic alkynes, were transformed at room temperature into the corresponding 1,3‐diynes in moderate to excellent yields. The turnover number was up to 1.04 × 10³. Copyright © 2015 John Wiley & Sons, Ltd.     

First report of a nano‐Cu2O‐catalyzed protocol for homo‐coupling reaction of terminal alkynes in water/ionic liquid medium

A new, efficient and green protocol for the nano‐Cu₂O‐catalyzed homo‐coupling reaction of terminal alkynes has been developed, using water/ionic liquid as an environmentally friendly solvent. Moreover, the system also allows the synthesis of unsymmetric 1,3‐diynes by cross‐coupling of two different terminal alkynes. It is noteworthy that the nano‐Cu₂O‐catalyzed methodology is a good supplement to copper catalyst for the Glaser‐type homo‐coupling reaction. Copyright © 2016 John Wiley & Sons, Ltd.     

A General and Highly Selective Palladium‐Catalyzed Hydroamidation of 1,3‐Diynes

A chemo‐, regio‐, and stereoselective mono‐hydroamidation of (un)symmetrical 1,3‐diynes is described. Key for the success of this novel transformation is the utilization of an advanced palladium catalyst system with the specific ligand Neolephos. The synthetic value of this general approach to synthetically useful α‐alkynyl‐α, β‐unsaturated amides is showcased by diversification of several structurally complex molecules and marketed drugs. Control experiments and density‐functional theory (M06L‐SMD) computations also suggest the crucial role of the substrate in controlling the regioselectivity of unsymmetrical 1,3‐diynes.     

An alternative CuCl–piperidine‐catalyzed oxidative homocoupling of terminal alkynes affording 1,3‐diynes in air

CuCl with the use of a catalytic amount of piperidine as additive shows high catalytic activity for the oxidative homocoupling reactions of terminal alkynes in toluene at 60 °C in air to afford 1,3‐diynes in high yields. Copyright © 2009 John Wiley & Sons, Ltd.     

Copper‐catalyzed homo‐ and cross‐coupling reactions of terminal alkynes in ethyl lactate

The bio‐based chemical ethyl lactate (EL) has been discovered to be an excellent medium for the Glaser‐type homo‐ and cross‐coupling reactions of terminal alkynes. Good to excellent yields of conjugate diynes have been obtained under ligand‐free and mild heating conditions in the presence of CuI and molecular oxygen. Copyright © 2014 John Wiley & Sons, Ltd.     

Chemo‐ and Regioselective Rhodium(I)‐Catalyzed [2+2+2] Cycloaddition of Allenynes with Alkynes

A highly chemo‐ and regioselective partially intramolecular rhodium(I)‐catalyzed [2+2+2] cycloaddition of allenynes with alkynes is described. A range of diverse polysubstituted benzene derivatives could be synthesized in good to excellent yields, in which the allenynes served as synthetic equivalent to the diynes. A high regioselectivity could be observed when allenynes were treated with unsymmetrical alkynes.     

Multicomponent Reactions of Pyridines To Give Ring‐Fused Pyridiniums: In Situ Activation Strategy Using 1,2‐Dichloroethane as a Vinyl Equivalent

Reported herein is a rhodium(III)‐catalyzed three‐component annulation reaction of simple pyridines, alkynes, and 1,2‐dichloroethane (DCE), affording a streamlined pathway to diverse ring‐fused pyridiniums. DCE not only serves as a vinyl equivalent but also as an in situ activating agent for pyridine C2?H activation. A cationic five‐membered rhodacycle complex has been isolated and proposed as a possible intermediate. This strategy can be extended to other N‐containing heteroarenes for the synthesis of multiring‐fused pyridiniums. These multicomponent reactions exhibit excellent regioselectivity for 1,3‐diynes, paving a path to the cascade cyclization of 3‐fluoropyridine or N‐methylpyridin‐3‐amine with 1,3‐diynes for the construction of brand‐new tricyclic‐fused pyrano‐ or hydropyridoquinolizinium salts. These ionic fluorophores have been investigated as potential biomarkers.     

Ligand-Free Synthesis of 1,4-Disubstituted-1,3-diynes by Iron/Copper Cocatalyzed Homocoupling of Terminal Alkynes

A simple and efficient protocol for Fe/Cu cocatalyzed oxidative homocoupling reaction of terminal alkynes to symmetrical 1,4‐disubstituted‐1,3‐diynes was presented. The results showed that both CuBr and FeCl₃ played crucial roles in the reaction. It is noteworthy that this protocol employs mild, efficient, aerobic and ligand free conditions. The alkynes, including aromatic, heteroaromatic and aliphatic alkynes, were transformed into the corresponding 1,3‐diynes in good to excellent yields.     

A reusable CuSO4 · 5H2O/cationic 2,2′‐bipyridyl system catalyzed homocoupling of terminal alkynes in water

A reusable CuSO₄ · 5H₂O/cationic 2,2′‐bipyridyl system catalyzed the homocoupling reaction of terminal alkynes in water using I₂ as the additive in the presence or absence of tetrabutylammonium bromide, giving the 1,3‐diynes in good to high yields. After reaction, the residual aqueous solution could be reused several times. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of Spirocyclic C‐Arylglycosides and ‐Ribosides by Ruthenium‐Catalyzed Cycloaddition

Spirocyclic C‐arylglycosides were synthesized from the appropriately protected δ‐gluconolactones. Addition of lithium acetylide followed by glycosylation with 3‐(trimethylsilyl)propargyl alcohol converted the δ‐gluconolactones into silylated diynes. After desilylation, subsequent ruthenium‐catalyzed cycloaddition of the resultant diynes with alkynes or chloroacetonitrile gave spirocyclic C‐arylglycosides in good yields and selectivity. This strategy was also extended to the synthesis of spirocyclic C‐arylribosides from the known γ‐ribonolactone derivative. Moreover, silver‐catalyzed iodination of the sugar diynes followed by ruthenium‐catalyzed cycloaddition with acetylene delivered spirocyclic C‐iodophenylglycosides and ‐ribosides, which were subjected to palladium‐catalyzed C? C bond‐forming reactions and copper‐catalyzed coupling with nitrogen heterocycles to lead to various derivatives.     

Brønsted Acid‐Catalyzed Three‐Component 1,3‐Dipolar Cycloadditions of 1,2‐Disubstituted Alkynes with Aldehyde‐Generated Azomethine Ylides

The first 1,3‐dipolar cycloadditions (1,3‐DCs) of 1,2‐disubstituted alkynes with aldehyde‐generated azomethine ylides have been established, leading to the efficient synthesis of poly‐substituted 2,5‐dihydropyrroles.The Brønsted acid‐catalyzed three‐component 1,3‐DCs of but‐2‐ynedioates, aldehydes, and diethyl 2‐aminomalonate tolerate a wide range of substrates, offering structurally diverse poly‐substituted 2,5‐dihydropyrroles in high yields. This protocol not only provides an easy and efficient approach to poly‐substituted 2,5‐dihydropyrroles but also greatly enriches the chemistry of 1,3‐DCs, especially alkyne‐involved 1,3‐DCs.     

Facilitating Gold Redox Catalysis with Electrochemistry: An Efficient Chemical‐Oxidant‐Free Approach

Due to the high oxidation potential between Au^I and Au^III, gold redox catalysis requires at least stoichiometric amounts of a strong oxidant. We herein report the first example of an electrochemical approach in promoting gold‐catalyzed oxidative coupling of terminal alkynes. Oxidation of Au^I to Au^III was successfully achieved through anode oxidation, which enabled facile access to either symmetrical or unsymmetrical conjugated diynes through homo‐coupling or cross‐coupling. This report extends the reaction scope of this transformation to substrates that are not compatible with strong chemical oxidants and potentiates the versatility of gold redox chemistry through the utilization of electrochemical oxidative conditions.     

Cobalt‐Catalyzed Alkenylzincation of Unfunctionalized Alkynes

While transition metal catalyzed addition reactions of arylmetal reagents to unfunctionalized alkynes have been extensively developed in the last decade, analogous reactions using alkenylmetal reagents remain rare regardless of their potential utility for the synthesis of unsymmetrical 1,3‐dienes. Reported herein is the development of a cobalt/diphosphine catalyst which promotes efficient and stereoselective addition of alkenylzinc reagents to unfunctionalized internal alkynes. The resulting dienylzinc species serve as versatile intermediates for further synthetic transformations.     

Gold‐Catalyzed Cadiot–Chodkiewicz‐type Cross‐Coupling of Terminal Alkynes with Alkynyl Hypervalent Iodine Reagents: Highly Selective Synthesis of Unsymmetrical 1,3‐Diynes

A new and efficient method for the synthesis of unsymmetrical 1,3‐butadiynes by gold‐catalyzed C(sp)–C(sp) cross‐coupling of terminal alkynes with alkynyl hypervalent iodine(III) reagents has been developed. The reaction features high selectivity and efficiency, mild reaction conditions, wide substrate scope, and functional‐group compatibility, and is a highly attractive complement to existing methods. Mechanistic studies reveal that formation of a phenanthrolinyl‐ligated gold(I) complex is crucial for the efficiency and selectivity of the target transformation.     

Catalytic Enantioselective Conjugate Alkynylation of α,β‐Unsaturated 1,1,1‐Trifluoromethyl Ketones with Terminal Alkynes

The first catalytic enantioselective conjugate alkynylation of α,β‐unsaturated 1,1,1‐trifluoromethyl ketones has been carried out. Terminal alkynes and 1,3‐diynes were treated with trifluoromethyl ketones in the presence of a low catalytic load of a Cu^I‐MeOBIPHEP complex (2.5 mol %) and triethylamine (10 mol %) to give the corresponding trifluoromethyl ketones bearing a propargylic stereogenic center at the β position with good yields and excellent enantiomeric excesses in most of the cases. No 1,2‐addition products were formed under the reaction conditions. The procedure showed broad substrate scope for alkyne, diyne, and enone. A rationale for the observed stereochemistry has been provided. Finally, the potential application of the reaction products in the synthesis of chiral tetrahydrofurans bearing a trifluoromethylated quaternary stereocenter has been devised.     

NHC–Pd(II) complex–Cu(I) co‐catalyzed homocoupling reaction of terminal alkynes

Two NHC–Pd(II) complexes synthesized from trans‐cyclohexane‐1,2‐diamine were fairly effective in the NHC–Pd(II) complex/Cu co‐catalyzed terminal alkyne homocoupling reaction to give the corresponding symmetrical 1,4‐disubstituted 1,3‐diynes in good yields under mild conditions. Copyright © 2006 John Wiley & Sons, Ltd.