Aryl-acetylene

When aiomatics aie present, they can capture the intermediate vinyl cation to give P-aryl-a,P-unsatutated ketones (182). Thus acylation of alkyl or aryl acetylenes with acyhum salts in the presence of aromatics gives a,P-unsaturated ketones with a trisubstituted double bond. The mild reaction conditions employed do not cause direct acylation of aromatics. 

Hydrogen chloride adds to aryl acetylenes in acetic acid to give mixtures of a-... 

The Pauson-Khand reaction was originally developed using strained cyclic alkenes, and gives good yields with such substrates. Alkenes with sterically demanding substituents and acyclic as well as unstrained cyclic alkenes often are less suitable substrates. An exception to this is ethylene, which reacts well. Acetylene as well as simple terminal alkynes and aryl acetylenes can be used as triple-bond component. 

Methanofullerene 20 with phenylacetylene dendrimer addends has also been reported [45] (Fig. 10). The UV absorption of fullerodendrimer 20 is particularly strong and is mainly attributed to transitions located on the two dendritic branches of the molecule. The photophysical investigations revealed that the large poly(aryl)acetylene branches act as photon antennae [46]. 

The utility of a palladium catalyst in the synthesis of substituted aryl acetylenes is well established.(7,8,9,10) The end-capping agent I was produced by using a standard catalyst system, dichlorobls(triphenylphosphlne)palladlum (II)/copper (I) iodide/triphenylphosphlne mixture, which has been employed in previously developed ethynylation procedures.(10) The copper (I) iodide is believed to act as a cocatalyst, reducing the palladium (II) complex to the active palladium (0) catalyst. The scheme is shown in Figure 3 (diethylamine is the solvent).(11)... 

Sonogashira has proposed a catalytic cycle (Figure 4) which shows 1) the reduction of the palladium complex, 2) coordination of the aryl halide and acetylene with the palladium (0) complex and 3) the reductive elimination of the substituted aryl acetylene and regeneration of the active catalyst.(10)... 

Aryl-acetylene synthesis, Cf. Cadiot-Chodkiewicz coupling and Sonogashira coupling. The Castro-Stephens coupling uses stoichiometric copper, whereas the Sonogashira variant uses catalytic palladium and copper. 

Regiochemistry of the obtained product leading to 1,1-disubstituted ethylenes is contrary to that observed in the addition of sodium butyltellurolate to aryl acetylenes, which produces exclusively the Z isomer resulting from an anti addition. ... 

Hydrazoic acid adds readily to acetylenes with electron-withdrawing groups, and less readily to alkyl and aryl acetylenes.Acetylene itself gives a high yield of i -triazole under carefully controlled conditions. Not all acetylenes give triazoles with hydrazoic acid. Open-chain azides have been obtained with ethoxyacetylene and with dimethyl acetylenedicarboxylate... 

Using Sonogashira conditions, the (R)-acetylenes (R)-904 and (R)-905 were coupled with M-carbethoxy-2-iodoaniline 700 to afford the aryl acetylenes (R)-906 and (R)-907. Executing similar functional group transformations as reported... 

Bowman et al. reported the total synthesis of ellipticine (228) involving an imidoyl radical cascade reaction (730). For this key step, the required imidoyl radical was generated from the imidoyl selanide 1290, which was obtained from ethyl 2-(4-pyridyl)acetate (1286). Reaction of 1286 with LDA, followed by addition of methyl iodide, led to the corresponding methyl derivative 1287. Treatment of 1287 with 2-iodoaniline (743) in the presence of trimethylaluminum (AlMes) afforded the amide 1288. Using Sonogashira conditions, propyne is coupled with the amide 1288 to afford the aryl acetylene 1289. The aryl acetylene 1289 was transformed to the... 

Aryl acetylenes undergo dimerization to give 1-aryl naphthalenes at 180 °C in the presence of ruthenium and rhodium porphyrin complexes. The reaction proceeds via a metal vinylidene intermediate, which undergoes [4 + 2]-cycloaddition vdth the same terminal alkyne or another internal alkyne, and then H migration and aromatization furnish naphthalene products [28] (Scheme 6.29). 

In the course of research on catalysis by synthetic metalloporphyrins, Tagliatesta and coworkers reported a unique cyclodimerization reaction of aryl acetylenes to give 2-aryl naphthalenes (6, Scheme 9.2) [5]. Ru(CO) and RhCl complexes effectively promote this reaction, with the latter catalyst (8) providing generally superior yields and selectivities for a small range of substrates (Table 9.1). As a synthetic method, Tagliatesta s cyclodimerization reaction is most remarkable for its efficiency. Yields of up to 78% were observed at a substrate/catalyst ratio of 5700 1. Successful recycling of recovered catalyst was also demonstrated. 

Hierso et al reported a copper-free, Sonogashira reaction for a number of activated and deactivated aryl halides with alkyl-/aryl acetylenes and using a variety of metallic precursors, bases and tertiary phosphanes in [bmim][BF4]. They found that a combination of [Pd(/7 -C3H5)Cl]2/PPh3 with 1 % pyrrolidine in the absence of copper showed the highest activity. 

Aryl acetylenic derivatives continue to exhibit interest as precursors for fused ring systems. Foe example, treatment of l-methyl-5-(trimethylsilylethynyl)uracil with ammonium fluoride leads to 3-methylfuro[2,3- 1pyrimidin-2(3//)-one in good yield <2006JMC391>. 

Addition of carbenes. Aryl acetylenes condense with the chlorinated oxocarbene 202 (35 hours at 100°) and give, through 1,3-cycloaddition, 3-substituted 4,5,6,7-tetrachloro-2-phenylbenzofurans (203).459 Compound 203 is readily dechlorinated (hydrogenation on Raney nickel in... 

Reactions of Ni(COD)2 with isocyanides in the presence of aryl acetylenes gave the products Ni4(CNR)4(ArC2Ar)3 (R = Bu, C6HM, Ar = Ph R = Bu, Ar = C6H4Me-p) together with Ni(ArC2Ar)(CNR)2. NMR studies on the addition of aryl acetylenes to Ni4(CNR)7 indicated only the formation of the trisacetylene adduct, with no evidence for intermediates being observed in this addition. However, addition of 3-hexyne to Ni4(CNBu )7... 

Another example of promising research is the efficient electrochemical dicarbo-xylations of aryl-acetylenes with C02, using an uncomplicated bimetallic redox couple as the catalytic system. In this case, metallic nickel was used as the cathode and aluminum as the anode, to generate in situ carboxylation-active nickel species (Scheme 5.20) [61]. 

Scheme 5.20 Ni-catalyzed electrochemical carboxylation of aryl-acetylenes without stabilizing ligands [61].

V-Tosylimines are alkynylated by aryl acetylenes in acetonitrile the reaction is promoted by zinc bromide and Hunig s base (A,A-diisopropylethylamine).74... 

In the alkyne dimerization catalyzed by palladium systems, all proposed mechanisms account for an alkynyl/alkyne intermediate with cis addition of the alkynyl C-Pd bond to the alkyne in a Markovnikov fashion, in which the palladium is placed at the less-substituted carbon, both to minimize steric hindrance and to provide the most stable C-Pd bond (Scheme 2a). The reverse regioselectivity in the palladium-catalyzed dimerization of aryl acetylenes has been attributed to an agostic interaction between the transition metal and ortho protons of the aromatic ring in the substrate (Scheme 2b) [7, 8],... 

The general catalytic cycle in the Pd(0)/Cu(I)-promoted aryl-acetylene coupling reaction is shown in Figure 8.3 [3],... 

Acetylene itself and alkyl- and aryl-acetylenes react with diazomethane under more severe conditions, such as 2-5 atmospheres, 20-40°.465-469 By this method 3,3 -dipyrazolyl (38) was synthesized... 

Hetaryl-substituted perfluoroalkyl(aryl)acetylenes, reactions with heterocycles 91UK1005. 

On the other hand, the catalytic system CpRu(CH3CN)3PF6/SnBr4 in the presence of lithium bromide in a less polar solvent such as acetone led to the favored formation of (Z)-vinyl bromides. Interestingly, when alkynes with a quaternary propargylic carbon or aryl acetylenes were used, complete selectivity for the (Z) isomer was obtained [60] (Eq. 46). 

Cocyclotrimerization of Aryl Acetylenes Substituent Effects on Reaction Rate... 

Cyclotrimerization of polyfunctional aryl acetylenes offers a unique route to a class of highly aromatic polymers of potential value to the micro-electronics industry. These polymers have high thermal stability and improved melt planarization as well as decreased water absorption and dielectric constant, relative to polyimides. Copolymerization of two or more monomers is often necessary to achieve the proper combination of polymer properties. Use of this type of condensation polymerization reaction with monomers of different reactivity can lead to a heterogeneous polymer. Accordingly, the relative rates of cyclotrimerization of six para-substituted aryl acetylenes were determined. These relative rates were found to closely follow both the Hammett values and the spectroscopic constants A h and AfiCp for the para substituents. With this information, production of such heterogeneous materials can be either avoided or controlled. 

One class of materials that minimizes both of these problems without compromising thermal stability is poly (aryl acetylenes). Over the past several years, two types of these polymers have been investigated in our laboratories diethynyl oligomers and cyclotrimerized multi-ethynyl aromatics (1). Examples of these two types of oligomers (1 and 2, respectively) are illustrated below. 

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