Phenylacetylene, reaction with ethyl

Phenylacetone, 54, 50 Phenylacetonitrile, 50, 20 Phenylacetylene, reaction with ethyl magnesium bromide,... 

Domino-Heck Reactions-General Procedure 5.6 mg (25 pmol) of palladium(II) acetate and 55 pmol of the arsine ligand were dissolved in 3 ml of dry dimethyl formamide and the solution was stirred at 65°C (40°C for trimethylsilylacetylene) for 15 mitt Then, 127 mg (1.35 mmol) N-Benzoyl-2-azabicyclo[2.2.1]hept-5-en-3-one, 1 mmol of the aryl compound. Four hundred and eighty-eight microliters (3.50 mmol) of triethylamine, and 3.00 mmol of the phenylacetylene (or silylmethyl-acetylene) were added rapidly in one portion. The mixture was heated at the same temperature for 24 h. After cooling down to room temperature 50 ml of brine were added, the reaction mixture was extracted with ethyl acetate and dried over MgSO. The solvent was evaporated, the residue purified by column chromatography (n-Hexan-Ethyl acetate 4 1). 

Interesting publications of work undertaken in this field of reactivity by a research group in (what at that time was part of) the USSR, unfortunately, was published mainly in rather inaccessible journals. The rates of reaction of phenylacetylene with ethyl- and phenylmagnesium bromide were measured in diethyl ether and in tetrahydrofuran, respectively [32]. The results, presented in Table 8, clearly show the dramatic change in the second-order rate constants, when diethyl ether is replaced by tetrahydrofuran as the solvent. The same effect had been found in 1968 by others [33] for the reaction of benzylmagnesium chloride with phenylacetylene at 0°C the second-order rate constant (/c2 X 10 L mol sec ) was 0.008 in diethyl ether and 84 in tetrahydrofuran, a change by a factor of (more than) 10 thousand. 

Thiaselenole-2-thiones undergo similar reactions. The cycloaddition of 5-phenyl-l,3-thiaselenole-2-thione (75) with ethyl propiolate gave two [3 + 2] cycloaddition products thione (76) and selenone (77) (80JHC549). Phenylacetylene was the neutral molecule lost in these reactions. 

Reaction Procedure (Scheme 2.61) To a mixture of Na2PdCl4 (12 mg, 0.0408 mmol) and sodium dodecyl sulfate (144 mg, 0.5 mmol) in water (3 mL) were added 2-iodophenol (220 mg, 1 mmol), phenylacetylene (123 mg, 1.2 mmol), and EtsN (303 mg, 3 mmol). The mixture was heated to reflux (oil bath) for 14 h (TLC). After cooling, the reaction mixture was extracted with ethyl acetate (3 x 10 mL). The extract was washed with water and brine and dried with Na2S04. Evaporation of the solvent left the crude product, which was purified by column chromatography over silica gel (hexane-ether, 92 8) to afford pure product. 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

Although the reaction of certain acetylenes such as phenylacetylene and ethyl phenylpropiolate with cold concentrated sulfuric acid to give acetophenone (15) and benzoylacetic acid (16) has been known since the 1880 s, it was only in the 1960 s that this reaction was studied mechanistically. 

A Michael-type addition reaction of phosphine generated from red phosphorus in concentrated aqueous KOH solution has been noted to provide moderate isolable yields of pure organophosphorus products.27 For example, tris-(2-cyanoethyl)phosphine is produced in 45% isolable yield from acrylonitrile, and tris-(2-[y-pyridyl]ethyl) phosphine oxide is isolated in 40% yield from 4-vinylpyridine under these conditions. Excellent yields of the tertiary phosphine oxide, tris-(2-cyanoethyl)phosphine oxide, have been reported using white phosphorus in absolute ethanol with KOH at ice/salt-bath temperatures.28 A variety of solvent systems were examined for this reaction involving a Michael-type addition to acrylonitrile. Similarly, tris-(Z-styryl)phosphine is produced from phenylacetylene under these conditions in 55% isolated yield. It is noteworthy that this last cited reaction involves stereospecific syn- addition of the phosphine to the alkyne. 

Nucleophilic attack of phosphines on 1,2,3-selenadiazoles leads to formation of selenophosphoranes and substituted acetylenes <2004CHE503>. Thus, 4-phenyl-1,2,3-selenadiazole 54 reacted with tributylphosphine in benzene at room temperature (Scheme 12). In the first stage, the Se-N bond is broken as a result of nucleophilic attack by tributylphosphine. Elimination of a molecule of nitrogen follows. A molecule of phenylacetylene is released from the intermediate and tributylselenophosporane 167 is produced. When triphenylphosphine is used, triphenylselenophos-phorane 168 is formed in quantitative yield after boiling for 1 h. In the reaction of 5-ethoxycarbonyM-mcthyl-1,2,3-selenadiazole 166 with phosphines, selenophosphoranes 167 and 168 are formed in 100% yield. Ethyl but-2-ynecarboxylate 169 was isolated from the reaction mixtures in 92% yield. 

Simultaneously and independently, similar results were obtained by the author s group47,49. It was observed that a short reflux (1-2 min) of an equimolecular mixture of chalcone 291 and A -ethylbenzonitrilium salt 35 in 1,2-dichloroethane furnishes the 2,4,6-triphenyl-3-ethyl-4//-l,3-oxazinium salt 38 (equation 81) obtained also by reaction of benzaldehyde with 35 and phenylacetylene (equation 15). If the salt 35 reacts with benzoylacetone 137 under the same conditions, 4-methylene-4//-l,3-oxazinium hexa-chloroantimonate 301 is formed47 (equation 82). 

Both pyrrole itself, as well as 4,5,6,7-tetrahydroindole underwent N-vinylation with 2-cyano-l-phenylacetylene in DMSO in the presence of KOH, while the treatment of 4,5,6,7-tetrahydroindole with 2-benzoyl-1-phenylacetylene under the same conditions furnished predominantly a C-vinylated product <03S1272>, Several functionalized 3-vinylpyrroles were prepared by reaction of pyrrole-3-carbodithioates with malonitrile, cyanacetamide, or ethyl cyanoacetate induced by KOH in DMSO <03TL3501>. 

However, in several special cases data on the possible formation of n-complexes with a monomeric form of OAC have been obtained. Thus, NMR studies have shown the formation of a n-complex by interaction of phenylacetylene with triethylaluminium. The heat of this reaction is 0.7 0.2 kcal/mol. Taking into account the heat of dissociation of an AljEtg molecule (17 kcal/mol the strength of the n-bond between phenylacetylene and aluminium ion is about 9 kcal/mol. The rate of phenylacetylene insertion into the aluminium-ethyl bond is first order with respect to the concentration of the -complex, according to reaction (18) ... 

---