Phenylethyne

Colan The trivial name given to di-phenylethyne (diphenyl acetylene), CflHs C = C CeHs- Obtained as volatile colourless crystals, m.p. 6TC, by HgO oxidation of benzil bis-hydrazone. 

The relative stabilities of 1-phenylvinyl cations can be measured by determining the gas-phase basicity of the corresponding alkynes. The table below gives some data on free energy of protonation for substituted phenylethynes and 1-phenylpropynes. These give rise to the corresponding Yukawa-Tsuno relationships. 

Bromoquinoline (70), behaving similarly to a simple carbocyclic aryl bromide, was coupled with phenylethyne 121 to provide disubstituted ethyne 122 in 50% yield (2001JCS(P1)978). 

Reactions between aldehydes and alkynes to give propargyl alcohols are also described in Kitazume and Kasai s paper [55]. Here, various aldehydes such as benzaldehyde or 4-fluorobenzaldehyde were treated with alkynes such as phenylethyne or pent-l-yne in three ionic liquids [EDBU][OTf], [BMIM][PFg], and [BMIM][BF4] (Scheme 5.1-27). A base (DBU) and Zn(OTf)2 were required for the reaction to be effective the yields were in the 50-70 % range. The best ionic liquid for this reaction depended on the individual reaction. 

As far as we are aware, the azo coupling of an ethyne derivative was only investigated over half a century ago Ainley and (Sir Robert) Robinson (1937) investigated the reaction of phenylethynes (phenylacetylenes) with diazonium ions (Scheme 12-59). Unsubstituted phenylethyne did not give identifiable products with the 4-nitrobenzenediazonium ion, but with the more nucleophilic 4-methoxyphenyl-ethyne an azo compound (12.119) was formed. On reaction with water it gives an arylhydrazone of an a-ketoaldehyde (12.120). 

Methanolysis of 26-ad gave mainly the product of a-elimination, phenylethyne (30), but a small amount of substitution product 29 was also obtained (eq 13). 16b The deuterium distributions in the isomeric products ( )-29 and (Z)-29 are very interesting and shed light on the reaction mechanisms for their formation. Due to the basicity of methanol, the main reaction path becomes a-elimination. The deuterium is completely scrambled in the E isomer of 29, as observed in the products of trifluoroethanolysis. In contrast, the Z isomer of 29, the product of inversion, retains the deuterium at the original a position. The best interpretation is that ( )-29 is formed via phenyl participation while (Z)-29 is produced via the in-plane SN2 reaction. 

Another new catalyst was described by Leardini and coworkers158, namely FeSC>4 in DMSO. It was applied to a Meerwein reaction of phenylethyne and substituted phenylethynes with arenediazonium salts containing a thioether group in the 2-position. 

Although the acylcobalt tetracarbonyls react with hydroxide ion under phase-transfer conditions, in the presence of alkenes and alkynes they form o-adducts rapidly via an initial interaction with the ir-electron system. Subsequent extrusion of the organometallic group as the cobalt tetracarbonyl anion leads to a,(J-unsaturated ketones (see Section 8.4). In contrast, the cobalt carbonyl catalysed reaction of phenylethyne in the presence of iodomethane forms the hydroxybut-2-enolide (5) in... 

Flash pyrolysis of l,4-bis(tetrazol-5-yl)benzene at 600°C has been explored as a possible route to the dicarbene, CH-C( H4-CH . The product was phenylethyne which carried a C label from the tetrazole C-5, confirming that a CgH, species had been generated <87JA2534>. Thermal degradation of C-labelled 5-diazotetrazole has provided a source of atomic carbon for carbene reactions... 

The alkyne 85 has been oxidatively dimerized with copper(I) salts giving and coupled with l-bromo-2-phenylethyne in the presence of copper (II) salts. The 9-phenacylcarbazole 88 was cleaved to 9-benzylcarbazole with strong aqueous alkali in hot glycol. 

Gibson and co-workers have introduced a well-designed latent cyclobutadiene moiety. Compound 49 reacts with a phenylethyne-cobalt complex to give PKR product 50 as a single diastereomer that resulted from the reaction at the less sterically hindered site, and 50 was subjected to the retro-Diels-Alder reaction at 205 °G under a vacuum of 6 torr to give 51 (Equation (23)). ... 

Aminocarbonylation has been combined with the Pauson-Khand reaction to construct fused tricyclic alkaloid skeletons (see 00154). The tandem aminocarbonylation/Pauson-Khand reaction of haloalkynes with a chiral allylic amine promoted by Co2(CO)8 gave angular triquinanes as exemplified in Scheme 25. Thus, the reaction of l-chloro-2-phenylethyne 175 with Co2(CO)8 at 0°C gave alkyne-dicobalt complex 176, which was converted to enoyl-dicobalt complex 177 upon warming to 25 °C. The reaction of enoyl-dicobalt complex 177 with cyclopente-nylmethyl(l-phenylethyl)amine 179 yielded Pauson-Khand reaction product, angular triquinane 180, via A -allylic aminocarbonylated alkyne-dicobalt complex 178 (Scheme 25). ... 

DMD-mediated oxidation of phenylethyne leads to the formation of phenylacetic acid, mandelic acid, and oligomeric mandelic acid, depending on the reaction conditions. The results have been explained by the initial formation of phenyloxirene, which equilibrates with phenylformylcarbene and benzoylcarbene (Scheme 8).211... 

The oxidation of phenylethyne with isolated dimethyldioxirane gives mandelic acid (61) and phenylacetic acid (60) as the main products.115 The formation of (60) and (61) is explained as involving the initial formation of phenyloxirene and therefore dimethyldioxirane-mediated oxidation of alkynes is potentially suited to study the chemistry of the elusive oxirenes. 

Reaction of 98 at 100 °C with alkenes or alkynes gives fused systems via 1,3-dipolar cycloaddition of a reactive azomethine ylide intermediate (see Section 2.04.6.1, Equation 7). For example, the reactions with phenylethyne and A-phenylmaleimide give the bicycle 99 and tricycle 100 products, respectively (Scheme 4). The reaction with A-phenylmaleimide shows second-order kinetics and first order with respect to 98 and the dipolarophile. However, surprisingly, in the absence of the dipolarophile, 98 does not lose CO2, but undergoes racemization. A mechanism for the process has been proposed and involves the initial formation of the ylide 101 and proton transfer to give ylide 102 which reacts with the dipolarophile. Selenopenams 103 have been synthesized by this method <1999JHC1365>. 

Recent development of a Ni catalysed alkylzincation of alkynes62 has further expanded the scope of both intramolecular and intermolecular carbozinca-tion. It should be noted, however, that carbozincation may be followed by cross-coupling under the reaction conditions. The current scope of the intramolecular process appears to be limited to five-membered ring formation, and that of the intermolecular version has been limited to phenylethyne derivatives (Scheme 11.18). Further exploration of the scope of this reaction is highly desirable. 

In order to avoid this unfavourable effect of the functional groups in the dendrimer structure, a rigid hydrocarbon backbone without heteroatoms was synthesized. Dendrimers with poly(phenylethyne) backbones, bearing three and six ephedrine derivatives at the periphery, were studied in the alkylation of aldehydes and N-diphenylphosphinylimines and proved to be highly en-antioselective catalysts. For example, the system containing six catalytic sites catalyzed the addition of diisopropylzinc to aldehydes with enantioselectivi-ties of up to 86% ee. As a third backbone a polycarbosilane dendrimer was used, which is chemically inert and more flexible than the poly(phenylethyne)... 

Oxidative coupling of phenylethynesis another Cu-catalyzed reaction that involves one-electron redox steps. Substituted, conjugated alkynes are valuable components for liquid crystal applications. Auer et al. (181) used a calcined CuMgAl-LDH-C03 to catalyze the air oxidation of phenylethyne to give l,4-diphenylbuta-l,3-diyne ... 

Sodium Pbenylethynetellurolate5 An apparatus suitable for work with liquid ammonia under a nitrogen atmosphere is set up. A 500-m/flask is charged with 250 ml of liquid ammonia freshly distilled from sodium. In the liquid ammonia are dissolved 1.15 g (0.05 mol) of sodium, a catalytic amount of iron(III) nitrate is added, and 5.1 g (0,05 mol) of phenylacetylenc are added dropwise over 0.5 h to the sodium amide solution. The mixture is allowed to stand for 40 min and then 6.4 g (0.05 mol) of finely powdered tellurium arc added to the sodium acetylide solution. The ammonia is evaporated and the residue of sodium phenylethyne-tellurolate can be dissolved in an appropriate solvent for further reactions. 

The reaction of tellurium with sodium phenylacetylide produced sodium phenylethyne-tellurolate that formed, on reaction with dimethyl acetylenedicarboxylate via cycloaddition, 2,3-bis[methoxycarbonyl]-4-phenyltellurophene as one of the tellurium-containing products2. The tellurophene derivative was separated and purified by chromatography on silica gel. 

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