Phenylethyne, oxidation

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 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. 

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. 

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 ... 

Auer, S. M., Wandeler, R., Gobel, U. and Baiker, A. (1997). Heterogeneous coupling of phenylethyne over Cu-Mg-Al mixed oxides - influence of catalyst composition and calcination temperature on structural and catalytic properties. J. Catal. 169, 1. 

Regardless of the mechanism, three clear generalizations concerning the reactions can be made. First, in cycloadditions to monosubstituted (alkyl/ aryl) alkynes only the 5-substituted isoxazole is obtained. Only in the case of perfluoroalkylalkynes has any significant amount of the 4-substituted isomer (31) been observed.89 Second, the reaction is hindered by bulky substituents on the alkyne. Finally, the reaction is not appreciably hindered by bulky substituents on the nitrile oxide, even when they are so large as to inhibit dimerization almost completely.59 Competition for phenylethyne between pentachloro- and pentabromobenzonitrile oxide gave approximately equimolar amounts of the two adducts (32)90... 

Phenylethyne also undergoes oxidative addition of the C—H bond to Ni(0) ... 

Phenylethyne also undergoes oxidative addition of the C—H bond to Ni(0) [Ni(PPh3)4] + PhCsCH—>[NiH(C=CPh)(PPh3)2] + 2PPh3... 

Palladium(O) complexes react with alkynes by oxidative addition of the C—H bond. The initial reaction of [Pd(PPh3)4] with phenylethyne presumably produces [PdH(CsCPh)(PPh3)2], but reaction with excess PhC=CH gives trans-[Pd(CsCCPh)2(PPh3)2 as the final product . 

Pentacarbonyl[cyclopropylethynyl(ethoxy)carbene]chromium complex 19 reacted with cyclo-penta-1,3-diene to give a cyclopropyl-substituted carbene complex of norbornadiene 22, which was converted to the corresponding carboxylic acid 23 upon oxidation or to a 1,4-quinone-type derivative 24 after Dotz-type cyclization with phenylethyne. ... 

Miller and coworkers treated 1-chloro- and l-bromO 2-phenylethyne with antimony pentafluoride in liquid sulphur dioxide benzene was added as a carbocation scavenger. Instead of carbon-halogen heterolysis they unexpectedly observed formation of 2-halo-3-phenylbenzothiophene 5 -oxide (41). On closer examination and depending upon substituent X various other products were observed, e.g. 1-halo-2,2-diphenylvinylsulphinic acids (42). The initial step in the formation of these products is probably electrophilic addition of sulphur dioxide, assisted by the Lewis acid. Trapping of the carbon cation by benzene and elimination of antimony pentafluoride explained the various products. 

C gave tributyl[(Z)-2-(phenylethynyl)ethenyl]tin 39 in good yield. The palladium-stannane complex (40), which could be generated by oxidative addition of Pd(0) coordinated by 38 onto C—Ph bond of phenylethyne, is assumed to involve the catalytic cycle (Scheme I7),[i t[i8]... 

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