Intermolecular Hydroamination of Alkynes Catalyzed by Dimethyltitanocene

A completely new application of dimethyltitanocene as catalyst for the intermolecular hydroamination of alkynes is presented. With this inexpensive and readily available catalyst, alkynes can be easily converted into imines, amines, and ketones (see reaction scheme).     

Sonogashira cross-coupling reactions catalysed by heterogeneous copper-free Pd-zeolites

A heterogeneous [Pd(NH₃)₄]-NaY catalyst was applied to the copper-free Sonogashira cross-coupling of aryl halides with terminal alkynes. This copper-free heterogeneous Pd-catalyst is efficient, stable and recyclable. Aryl iodides and activated aryl bromides were converted quantitatively using 1 mol % Pd-catalyst to the corresponding diaryl-substituted alkynes within 3 h.     

An efficient and facile one-pot synthesis of propargylamines by three-component coupling of aldehydes, amines, and alkynes via C-H activation catalyzed by NiCl2

NiCl₂ was found to be a highly efficient and effective catalyst for the one-pot three-component (A³) coupling of aldehydes, amines, and alkynes to produce propargylamines in nearly quantitative yields. Structurally divergent aldehydes, amines, and alkynes were converted into the corresponding propargylamines. No co-catalyst or activator is needed and water is the only byproduct of this novel protocol.     

Cobalt‐Catalyzed Alkyne Hydrosilylation and Sequential Vinylsilane Hydroboration with Markovnikov Selectivity

A pyridinebis(oxazoline) cobalt complex is a very efficient precatalyst for the hydrosilylation of terminal alkynes with Ph₂SiH₂, providing α‐vinylsilanes with high (Markovnikov) regioselectivity and broad functional‐group tolerance. The vinylsilane products can be further converted into geminal borosilanes through Markovnikov hydroboration with pinacolborane and a bis(imino)pyridine cobalt catalyst.     

Au(Ⅰ)配合物催化剂室温高效催化炔烃水合反应

合成了一系列(1,1'-联苯)-2-二(1-金刚烷基)磷配体, 并制备出8种相应的Au(Ⅰ)配合物. 以甲醇为溶剂, 在6-十二炔水合反应中考察了8种Au(Ⅰ)配合物的催化性能, 结果表明, 以含有3'-(吡咯-1-羰基)官能团的Au(Ⅰ)配合物为催化剂时, 其用量仅需炔烃用量的0.1%~0.3%(摩尔分数), 室温下即可高效地催化炔烃进行水合反应.     

An efficient synthesis of propargylamines via three-component coupling of aldehydes, amines and alkynes catalyzed by nanocrystalline copper(II) oxide

An efficient three-component coupling of aldehydes, amines and alkynes to prepare propargylamines, in nearly quantitative yields using nanocrystalline CuO as a catalyst is described. Structurally divergent aldehydes and amines were converted to the corresponding propargylamines. The reaction does not require any co-catalyst. After completion of the reaction, the catalyst was recovered by centrifugation and reused several times with only a slight decrease of activity observed under the same reaction conditions.     

Fast, ligand- and solvent-free synthesis of 1,4-substituted buta-1,3-diynes by Cu-catalyzed homocoupling of terminal alkynes in a ball mill

A method for the Glaser coupling reaction of alkynes by using a vibration ball mill has been developed. The procedure avoids the use of ligands and solvents during the reaction. Aryl- and alkyl-substituted terminal alkynes undergo homocoupling if coground with KF-Al(2)O(3) and CuI as a milling auxiliary and catalyst. Furthermore, an alternative protocol has been developed incorporating 1,4-diazabicyclo[2.2.2]octane (DABCO) as an additional base allowing the use of KF-Al(2)O(3) with a lower KF loading. Besides Cu salts, the homocoupling of phenylacetylene is also catalyzed by Ni or Co salts, as well as by PdCl(2). TMS-protected phenylacetylene could be directly converted into the homocoupling product after in situ deprotection of the alkyne by fluoride-initiated removal of the trimethylsilyl group.     

Photoactivated hydrosilylation reaction of alkynes

The photoactivated (350 nm) hydrosilylation of alkynes by silanes catalyzed by platinum(II) bis(acetylacetonato) has been studied. Platinum(II) bis(acetylacetonato) is an efficient catalyst. High yields of adducts (>98% for terminal alkynes) can be obtained in 2–3 h after a short induction period with a catalyst–reactant molar ratio of 10⁻³/1. The reaction rate depends on the choice of silane, irradiation time and the concentration of catalyst. The major product is the β-trans adduct. Minor products are the α isomer with a trace of β-cis isomer. Comparisons of hydrosilylation reactions of alkynes with hydrosilylation reactions of alkenes are reported.     

Highly Efficient and Stereoselective Thioallylation of Alkynes: Possible Gold Redox Catalysis with No Need for a Strong Oxidant

Stereoselective thioallylation of alkynes under possible gold redox catalysis was accomplished with high efficiency (as low as 0.1 % catalyst loading, up to 99 % yield) and broad substrate scope (various alkynes, inter‐ and intramolecular fashion). The gold(I) catalyst acts as both a π‐acid for alkyne activation and a redox catalyst for Au^I/III coupling, whereas the sulfonium cation generated in situ functions as a mild oxidant. This novel methodology provides an exciting system for gold redox catalysis without the need for a strong oxidant.     

Cobalt‐Catalyzed Cyclization of N‐Methoxy Benzamides with Alkynes using an Internal Oxidant through C−H/N−O Bond Activation

The cyclization of substituted N‐methoxy benzamides with alkynes in the presence of an easily affordable cobalt complex and NaOAc provides isoquinolone derivatives in good to excellent yields. The cyclization reaction is compatible with a range of functional group‐substituted benzamides, as well as ester‐ and alcohol‐substituted alkynes. The cobalt complex [Co^IIICp*(OR)₂] (R=Me or Ac) serves as an efficient catalyst for the cyclization reaction. Later, isoquinolone derivatives were converted into 1‐chloro and 1‐bromo substituted isoquinoline derivatives in excellent yields in the presence of POCl₃ or PBr₃.     

Syntheses and synthetic applications of stannylated allylic alcohols

Allenyl carbinols undergo regioselective hydrostannation in the presence of MoBl3, a catalyst originally developed for the hydrostannation of alkynes, giving rise to allyl stannanes. These allyl stannanes can easily be converted into useful synthetic building blocks such as allyl iodides or vinyl epoxides.     

TiCl4/t-BuNH2 as the sole catalyst for a hydroamination-based Fischer indole synthesis

A system comprising TiCl₄ and t-BuNH₂ acts as a catalyst for highly regioselective hydroamination reactions of alkynes using hydrazines and at the same time a Lewis acid in the transformation of the generated hydrazones into indole derivatives, while a 1,3-diyne is converted to pyrroles using the same precatalyst.     

A Simple Efficient Click Synthesis of Novel Crown Ethers Containing 1,2,3-Triazole Moieties

Novel crown ether derivative containing 1,4-disubstituted-1,2,3-triazole moieties were synthesized. At the first step of the synthesis 4,13-diaza-18-crown-6 and 4-aminobenzo-15-crown-5 were converted into terminal alkynes, which were then subjected to copper(I)-catalyzed alkyne-azide coupling (CuAAC) in methylene chloride. This coupling reaction was performed according to the concept of click chemistry, using an Amberlyst A-21-supported copper(I) iodide catalyst.

     

Heterogeneously catalyzed efficient hydration of alkynes to ketones by tin-tungsten mixed oxides

The Sn–W mixed oxide prepared by calcination of the Sn–W mixed hydroxide precursor with a Sn/W molar ratio of 2:1 at 800 °C (SnW2‐800) acts as an efficient heterogeneous catalyst for the hydration of alkynes. Structurally diverse terminal and internal alkynes, including aromatic, aliphatic, and double‐bond‐containing ones, can be converted into the corresponding ketones in moderate to high yields. The catalytic activity of SnW2‐800 is much higher than those of previously reported heterogeneous catalysts and commonly utilized acid catalysts. The observed catalysis was truly heterogeneous, and the retrieved catalyst can be reused at least three times with retention of its high catalytic performance. The reaction rate for the SnW2‐800‐catalyzed hydration was decreased by addition of 2,6‐lutidine and the hydration hardly proceeded in the presence of an equimolar amount of this compound with respect to that of the Brønsted acid sites in SnW2‐800. Therefore, the present hydration is mainly promoted by the Brønsted acid sites in SnW2‐800.     

Synthesis of Triborylalkenes from Terminal Alkynes by Iridium‐Catalyzed Tandem C?H Borylation and Diboration

A two‐step reaction to convert terminal alkynes into triborylalkenes is reported. In the first step, the terminal alkyne and pinacolborane (HBpin) are converted into an alkynylboronate, which is catalyzed by an iridium complex supported by a SiNN pincer ligand. In the second step, treatment of the reaction mixture with CO generates a new catalyst which mediates dehydrogenative diboration of alkynylboronate with pinacolborane. The mechanism of the diboration remains unclear but it does not proceed via intermediacy of hydroboration products or via B₂pin₂.     

Synthesis of Triborylalkenes from Terminal Alkynes by Iridium‐Catalyzed Tandem CH Borylation and Diboration

A two‐step reaction to convert terminal alkynes into triborylalkenes is reported. In the first step, the terminal alkyne and pinacolborane (HBpin) are converted into an alkynylboronate, which is catalyzed by an iridium complex supported by a SiNN pincer ligand. In the second step, treatment of the reaction mixture with CO generates a new catalyst which mediates dehydrogenative diboration of alkynylboronate with pinacolborane. The mechanism of the diboration remains unclear but it does not proceed via intermediacy of hydroboration products or via B₂pin₂.     

Encapsulation of Palladium Carbide Subnanometric Species in Zeolite Boosts Highly Selective Semihydrogenation of Alkynes

The selective hydrogenation of alkynes to alkenes is a crucial step in the synthesis of fine chemicals. However, the widely utilized palladium (Pd)-based catalysts often suffer from poor selectivity. In this work, we demonstrate a carbonization-reduction method to create palladium carbide subnanometric species within pure silicate MFI zeolite. The carbon species can modify the electronic and steric characteristics of Pd species by forming the predominant Pd−C₄ structure and, meanwhile, facilitate the desorption of alkenes by forming the Si−O−C structure with zeolite framework, as validated by the state-of-the-art characterizations and theoretical calculations. The developed catalyst shows superior performance in the selective hydrogenation of alkynes over mild conditions (298 K, 2 bar H₂), with 99 % selectivity to styrene at a complete conversion of phenylacetylene. In contrast, the zeolite-encapsulated carbon-free Pd catalyst and the commercial Lindlar catalyst show only 15 % and 14 % selectivity to styrene, respectively, under identical reaction conditions. The zeolite-confined Pd-carbide subnanoclusters promise their superior properties in semihydrogenation of alkynes.     

Cobalt‐Catalyzed Intermolecular [2+2] Cycloaddition between Alkynes and Allenes

An intermolecular [2+2] cycloaddition reaction between an alkyne and an allene is reported. In the presence of a cobalt(I)/diphosphine catalyst, a near equimolar mixture of the alkyne and allene is converted into a 3‐alkylidenecyclobutene derivative in good yield with high regioselectivity. The reaction tolerates a variety of internal alkynes and mono‐ or disubstituted allenes bearing various functional groups. The reaction is proposed to involve regioselective oxidative cyclization of the alkyne and allene to form a 4‐alkylidenecobaltacyclopentene intermediate, with subsequent C?C reductive elimination.     

A [2+2+2]‐Cyclotrimerization Approach to Selectively Substituted Fluorenes and Fluorenols,and Their Conversion to 9,9′‐Spirobifluorenes

Synthesis of selectively substituted fluorenes and fluorenols was achieved by using catalytic [2+2+2]cyclotrimerization. Various starting diynes were reacted with different alkynes in the presence of a catalytic amount of Wilkinson’s catalyst (RhCl(PPh₃)₃) providing the compounds possessing the fluorene scaffold in good isolated yields. A set of four regioselectively substituted fluorenols was converted to the corresponding 9,9′‐spirobifluorenes and their spectral characteristics were measured.     

Efficient alkyne homocoupling catalysed by copper immobilized on functionalized silica

Copper immobilized on a functionalized silica support is a good catalyst for the homocoupling of terminal alkynes. The so‐called Glaser–Hay coupling reaction can be run in air with catalytic amounts of base. The copper catalyst is active for multiple substituted alkynes, in both polar and non‐polar solvents, with good to excellent yields (75–95%). Depending on the alkyne, full conversion can be achieved within 3–24 h. The catalyst was characterized by TGA, inductively coupled plasma and X‐ray photoelectron spectroscopy. Leaching tests confirm that the catalyst is and remains heterogeneous. Importantly, the overall reaction requires only alkyne and oxygen (in this case, air) as reagents, making this a clean catalytic oxidative coupling reaction. Copyright © 2012 John Wiley & Sons, Ltd.