Coupling reactions acetylenic

Coupling Reactions.—Acetylenes react with organoalanes, e.g. MesAl, and zirconocene dichloride to form the alkenyl metal complexes (38) in high yield. The exact structure of these complexes is not known but both aluminium and zirconium are essential. The stereoselectivity of the reaction is shown to be 98% c/s-addition, and once formed the complexes (38) undergo a variety of useful... 

Monosubstitution of acetylene itself is not easy. Therefore, trimethylsilyl-acetylene (297)[ 202-206] is used as a protected acetylene. The coupling reaction of trimethylsilylacetylene (297) proceeds most efficiently in piperidine as a solvent[207]. After the coupling, the silyl group is removed by treatment with fluoride anion. Hexabromobenzene undergoes complete hexasubstitution with trimethylsilylacetylene to form hexaethynylbenzene (298) after desilylation in total yield of 28% for the six reactions[208,209]. The product was converted into tris(benzocyclobutadieno)benzene (299). Similarly, hexabutadiynylben-zene was prepared[210j. 

The copper species formed depends on the solvent, and three different species were detected by F NMR, although the structure of each species was not elucidated [245 This copper reagent undergoes a variety of coupling reactions with aryl, alkenyl, allyl, and acetylenic halides [244, 245 (equation 162)... 

Copper(I) halide-catalyzed coupling reactions of perfluoro Gngnard reagents with allyl and propargyl halides have been reported [256], The acetylenic copper compound may be an intermediate in these reactions. 

The high reactivity of monosubstituted acetylenes in many reactions (acetylenic condensation, Favorsky reaction, Mannich reaction, oxidative coupling, etc.) is determined by their acidity (7IMI1 83MI1). The literature data on the thermodynamic CH acidity of these compounds are rather scarce. 

The synthesis can be conducted both in solution and without solvents. The reaction in solvent (e.g., methanol, ethanol, dioxane, dimethylformamide) is recommended for volatile 1,3-diynes and amines in this case the pyrroles are purer and the yield is higher. With disubstituted diacetylenes, ammonia and primary alkyl- and arylamines produce 1,2,3-trisubstituted pyrroles under the same conditions (65CB98 71MI1). Since disubstituted diacetylenes are readily obtained by oxidative coupling of acetylenes (98MI2), this reaction provides a preparative route to a wide range of pyrroles. 

Due to their successful synthesis of 2-(4 -chlorophenyl)-4-iodoquinoline from the corresponding precursor acetylene, Arcadi et al. (99T13233) developed a one-step synthesis of 2,4-disubstituted quinolines via palladium-catalyzed coupling reactions. An example is the Heck reaction of 4-iodoquinoline (131) with a-acetamidoacrylate (132). This one-pot synthesis yielded adduct 133 in 50% overall yield after purification via flash chromatography. 

Keywords Acetylene chemistry. Cross-coupling reactions, Cyclo[n]carbons, Expanded radialenes. Molecular scaffolding. Nanostructures, Perethynylated chromophores, Poly(triacetylene), Tetraethynylethene. 

Over the last decade, the chemistry of the carbon-carbon triple bond has experienced a vigorous resurgence [1]. Whereas construction of alkyne-con-taining systems had previously been a laborious process, the advent of new synthetic methodology based on organotransition metal complexes has revolutionized the field [2]. Specifically, palladium-catalyzed cross-coupling reactions between alkyne sp-carbon atoms and sp -carbon atoms of arenes and alkenes have allowed for rapid assembly of relatively complex structures [3]. In particular, the preparation of alkyne-rich macrocycles, the subject of this report, has benefited enormously from these recent advances. For the purpose of this review, we Emit the discussion to cychc systems which contain benzene and acetylene moieties only, henceforth referred to as phenylacetylene and phenyldiacetylene macrocycles (PAMs and PDMs, respectively). Not only have a wide... 

The Sonogashira reaction is a transition metal-catalyzed coupling reaction which is widely used for the preparation of alkyl-, aryl- and diaryl-substituted acetylenes (Table 4.7) [120]. This reaction is a key step in natural product synthesis and is also applied in optical and electronic applications. Sonogashira reactions involve the use of an organic solvent with a stoichiometric portion of a base for capturing the... 

C-TMS protection of the alkyne provided acceptable yields of 3-substituted indole as long as the hydroxy group was protected with a stable group. Purple colored impurities, one of which has been identified as azulene 45, were seen in both coupling reactions using C-TMS-alkynes such as 36 and 40d (Scheme 4.9). The azulene was presumably formed through the dimerization of acetylenes... 

Besides palladium catalysts, nickel was also found to be an effective catalyst for the Sonogashira reaction in aqueous media. Recently, Beletskaya et al. reported a Ni(PPh3)2Cl2/CuI-catalyzed Sonogashira coupling reaction of terminal acetylenes with aryl iodides in aqueous dioxane in high yields (Eq. 4.19).39... 

There are many other transition-metal catalyzed coupling reactions that are based on organic halides in aqueous media. One example is the coupling of terminal alkyne with aryl halides, the Sonogashira coupling, which has been discussed in detail in the chapter on alkynes (Chapter 4). An example is the condensation of 2-propynyl or allyl halides with simple acetylenes in the presence of copper salts. 

Cross-coupling reactions with Zn acetylenides are the most convenient and selective routes to terminal acetylenes. In this reaction Zn is markedy superior to other metals, including Sn (24).116 The higher reactivity of Zn acetylides allowed assembly of hexaethynylbenezenes in two steps, with the last three groups introduced at the second stage by the Negishi reaction (25).117... 

In the SH reaction acetylenes are used as they are, without the prior transformation into organometallic compounds which is required in other methods of coupling. The SH... 

So far, no systematic work has been done on the use of recyclable, solid-phase catalysts in cross-coupling reactions. Most of the examples have been obtained for cross-couplings with either arylboronic acids or terminal acetylenes. It should be noted, however, that due care should be exercised when interpreting results on the cross-coupling of arylboronic acids with aryl iodides, as this extremely facile reaction can be catalyzed by practically any palladium-containing material, including trivial Pd black,481 e.g., as a sediment on the reaction vessel. Therefore, this reaction cannot serve as a reliable test for comparison between different catalytic systems. 

Synthesis of Functionalized Enynes by Palladium/Copper-catalyzed Coupling Reactions of Acetylenes with (Z)-2,3-Dibromopropenoic Acid Ethyl Ester (Z)-2-Bromo-5-(trimethylsilyl)-2-penten-4-ynoic Acid Ethyl Ester. 

A variety of triazole-based monophosphines (ClickPhos) 141 have been prepared via efficient 1,3-dipolar cycloaddition of readily available azides and acetylenes and their palladium complexes provided excellent yields in the amination reactions and Suzuki-Miyaura coupling reactions of unactivated aryl chlorides <06JOC3928>. A novel P,N-type ligand family (ClickPhine) is easily accessible using the Cu(I)-catalyzed azide-alkyne cycloaddition reaction and was tested in palladium-catalyzed allylic alkylation reactions <06OL3227>. Novel chiral ligands, (S)-(+)-l-substituted aryl-4-(l-phenyl) ethylformamido-5-amino-1,2,3-triazoles 142,... 

The Fukuyama indole synthesis involving radical cyclization of 2-alkenylisocyanides was extended by the author to allow preparation of2,3-disubstituted derivatives <00S429>. In this process, radical cyclization of 2-isocyanocinnamate (119) yields the 2-stannylindole 120, which upon treatment with iodine is converted into the 2-iodoindole 121. These N-unprotected 2-iodoindoles can then undergo a variety of palladium-catalyzed coupling reactions such as reaction with terminal acetylenes, terminal olefins, carbonylation and Suzuki coupling with phenyl borate to furnish the corresponding 2,3-disubstituted indoles. 

Dipolar cycloaddition reaction of trimethylstannylacetylene with nitrile oxides yielded 3-substituted 5-(trimethylstannyl)isoxazoles 221. Similar reactions of (trimethylstannyl)phenylacetylene, l-(trimethylstannyl)-l-hexyne, and bis (trimethylsilyl)acetylene give the corresponding 3,5-disubstituted 4-(trimethyl-stannyl)isoxazoles 222, almost regioselectively (379). The 1,3-dipolar cycloaddition reaction of bis(tributylstannyl)acetylene with acetonitrile oxide, followed by treatment with aqueous ammonia in ethanol in a sealed tube, gives 3-methyl-4-(tributylstannyl)isoxazole 223. The palladium catalyzed cross coupling reaction of... 

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