3- Hexyne phenylacetylene

CONDENSATIONS WITH SODAMIDE IN LIQUID AMMONIA Acetylenic compounds are conveniently prepared with the aid of Uquid ammcx as a solvent. The preparation of a simple acetylenic hydrocarbon ( -butylacetylene or 1-hexyne) and also of phenylacetylene is described. Experimental details are also given for two acetylenic carbinols, viz., 1-ethynyl-eyciohoxanul and 4-pentyn-l-ol. It will be noted that the scale is somewhat laige smaller quantities can readily be prepared by obvious modifications of the directions. 

Examples of perfluoroalkyl iodide addition to the triple bond include free radical addition of perfluoropropyl iodide to 1 -heptyne [28] (equation 21), thermal and free radical-initiated addition of lodoperfluoroalkanesulfonyl fluorides to acetylene [29] (equation 22), thermal addition of perfluoropropyl iodide to hexa-fluoro 2 butyne [30] (equation 23), and palladium-catalyzed addition of per-fluorobutyl iodide to phenylacetylene [31] (equation 24) The E isomers predominate in these reactions Photochemical addition of tnfluoromethyl iodide to vinylacetylene gives predominantly the 1 4 adduct by addition to the double bond [32] Platinum catalyzed addition of perfluorooctyl iodide to l-hexyne in the presence of potassium carbonate, carbon monoxide, and ethanol gives ethyl () per fluorooctyl-a-butylpropenoate [JJ] (equation 25)... 

However, a number of examples have been found where addition of bromine is not stereospecifically anti. For example, the addition of Bf2 to cis- and trans-l-phenylpropenes in CCI4 was nonstereospecific." Furthermore, the stereospecificity of bromine addition to stilbene depends on the dielectric constant of the solvent. In solvents of low dielectric constant, the addition was 90-100% anti, but with an increase in dielectric constant, the reaction became less stereospecific, until, at a dielectric constant of 35, the addition was completely nonstereospecific.Likewise in the case of triple bonds, stereoselective anti addition was found in bromination of 3-hexyne, but both cis and trans products were obtained in bromination of phenylacetylene. These results indicate that a bromonium ion is not formed where the open cation can be stabilized in other ways (e.g., addition of Br+ to 1 -phenylpropene gives the ion PhC HCHBrCH3, which is a relatively stable benzylic cation) and that there is probably a spectrum of mechanisms between complete bromonium ion (2, no rotation) formation and completely open-cation (1, free rotation) formation, with partially bridged bromonium ions (3, restricted rotation) in between. We have previously seen cases (e.g., p. 415) where cations require more stabilization from outside sources as they become intrinsically less stable themselves. Further evidence for the open cation mechanism where aryl stabilization is present was reported in an isotope effect study of addition of Br2 to ArCH=CHCHAr (Ar = p-nitrophenyl, Ar = p-tolyl). The C isotope effect for one of the double bond carbons (the one closer to the NO2 group) was considerably larger than for the other one. ... 

Whereas cyclotrimerization of phenylacetylene with uncomplexed PdCl2 provides only low yields of the unsymmetrical trimer, and polymers, on treatment of 3-hexyne with Pd/C and Me3SiCl 14 hexaethylbenzene 2165 is obtained in quantitative yield [78] (Scheme 13.23). 

However, with 1-hexyne or phenylacetylene, the thorium catalyst induces a dramatic inversion in regioselectivity giving imines with various amounts of dimerized alkyne (e.g., Eq. 4.84) [301],... 

The use of stronger acid conditions provides somewhat better synthetic yields of alkanes from alkynes. A useful method consists of treatment of the substrate with a combination of triethylsilane, aluminum chloride, and excess hydrogen chloride in dichloromethane.146 Thus, treatment of phenylacetylene with 5 equivalents of triethylsilane and 0.2 equivalents of aluminum chloride in this way at room temperature yields 50% of ethylbenzene after 1.5 hours. Diphenylacetylene gives a 50% yield of bibenzyl when treated with 97 equivalents of triethylsilane and 2.7 equivalents of aluminum chloride after 2.8 hours. Even 1-hexyne gives a mixture of 44% n -hexane and 7% methylpentane of undisclosed structure when treated with 10 equivalents of triethylsilane and 0.5 equivalent of aluminum chloride for 0.5 hour.146... 

Platinum on carbon did almost exactly the same thing but required a temperature of about 100°C to do so. With excess acetylene, only III formed. With tcrt-butylacetylene no II formed, probably because of steric hindrance, but I and III formed readily. 3-Hexyne reacted more slowly, required heat with chloroplatinic acid, and formed exclusively c/s-3-di-chlorosilyl-3-hexene. Trichlorosilane with platinum on carbon also added (57) to 1-alkynes or to phenylacetylene exclusively by cis addition to give only trans adducts. Later works (55) indicate that chloroplatinic acid and other soluble catalysts also give exclusively cis addition with a wide variety of Si—H compounds. 

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... 

Finally, the only example of a polynuclear homogeneous catalyst is the dinuc-lear complex [Pt P sH ]4- [66], which catalyzed the hydrogenation of styrene, phenylacetylene, 1-octyne, and 1-hexyne (i-PrOH, 60°C, 20.7 atm H2 pressure, Pd substrate ratio 1 1800) to the corresponding alkanes within 10 h of reaction. 

A Ni(dppe)Br2-Zn system effectively catalyzes co-cydotrimerization of an allene with a propiolate. The reaction is highly regio- and chemoselective to afford a poly-substituted benzene derivative in good yield. (Scheme 16.82) [92], From the observation that no desired [2 + 2 + 2] product is obtained for the reaction of 1-hexyne and phenylacetylene with w-butylallene under similar conditions, the presence of an electron-withdrawing C02Me group in the alkyne moiety is essential for the success of the present [2 + 2 + 2]-co-cyclotrimerization. 

The method has been applied by the submitters2 to the preparation of cyclohexylmethylpropiolaldehyde diethyl acetal (54% yield) from cyclohexylmethylacetylene and triethyl orthoformate of phenylethynyl n-butyl dimethyl ketal (40% yield) from phenylacetylene and trimethyl -orthovalerate and of phenylethynyl methyl diethyl ketal (34% yield) from phenylacetylene and triethyl orthoacetate. w-B utylpropiolaldehyde diethyl acetal was isolated in 32% yield by heating an equimolar mixture of 1-hexyne and triethyl orthoformate containing catalytic amounts of a zinc chloride-zinc iodide catalyst under autogenous pressure at 190° for 3 hours. 

Since the substitution reaction succeeded so well with olefins, the obvious extension to acetylenes was tried. Of course, only terminal acetylenes could be used if an acetylenic product was to be formed. This reaction has been found to occur but probably not by a mechanism analogous to the reaction of olefins (43,44). It was found that the more acidic acetylene phenylacetylene reacted with bromobenzene in the presence of triethylamine and a bisphos-phine-palladium complex to form diphenylacetylene, while the less acidic acetylene, 1-hexyne did not react appreciably under the same conditions. The reaction did occur when the more basic amine piperidine was used instead of triethylamine, however (43). Both reactions occur with sodium methoxide as the base (44). It therefore appears that the acetylide anion is reacting with the catalyst and that a reductive elimination of the disubstituted acetylene is... 

The diphosphine of choice for obtaining good regioselectivity is the bis(diphe-nylphosphino)butane (Scheme 4). It enables addition of a variety of carboxylic acids to phenylacetylene and hexyne. The reaction temperature, which enables complete conversion can be reduced from 80 to 0 °C when the acidity of the carboxylic acid increases in the pK, range from 5 to 1.5. The milder temperature conditions always lead to higher regioselectivity of the addition. The preparation of functionalized (Z)-cnol esters can be conducted in apolar solvents such as toluene or pentane dienyl esters are selectively produced from conjugated enynes [9]. 

Isolation of the air-sensitive silacyclopropene was avoided by development of a two-step, one-flask procedure, which transformed alkynes into the desired azasilacyclopentadienes (Scheme 7.29)." For terminal alkynes, silver phosphate was employed for di-terf-butylsilylene transfer and copper(I) triflate was used to promote nitrile insertion. These conditions successfully transformed phenylacetylene into azasilacyclopentadiene 106b. For internal alkynes, copper(I) triflate catalyzed both silylene transfer to 3-hexyne as well as nitrile insertion to produce enamine 106k. 

Arene ruthenium(II) complexes have been shown to catalyze the re-gioselective addition of ammonium carbamate to terminal alkynes, such as phenylacetylene and 1-hexyne, to produce vinylcarbamates. 

Activation entropies of — 29 and — 51 cal. mol-1K-1 have been calculated for k2 and k3 respectively in the case of tolylacetylene and the difference is that expected between a bimolecular and a termolecular event. A value of AS of - 41 cal. mol-1 K 1 for k2 in the case of 3-hexyne indicates a more ordered transition state than in the case of phenylacetylene derivatives. 

Also from this study the difference in the rate of bromination of alkenes and alkynes is quite evident. Thus the bimolecular coefficient (k2) for styrene is 2 x 103 times that for phenylacetylene and k2 for 3-hexene is 1-4 x 105 times the value for 3-hexyne. Since the first two compounds are believed to react via carbonium ions and the latter two via bromonium ions there seems to be an extra factor of 102 in the stability of bromonium ions from alkenes relative to those from alkynes. 

Monosubstituted acetylene polymers with relatively small steric effect, naturally, show properties intermediate between those of the two extremes in Table 25. For example, poly(l-hexyne) and poly(phenylacetylene) are dark brown to yellow, more or less sensitive to air, and somewhat paramagnetic. In the following discussion, individual properties of not these polyacetylenes but those with large steric effect will be mostly described. 

Preparation of the in situ Catalyst and Catalytic Reaction. (This is a typical procedure for norbomadiene and phenylacetylene or 1-hexyne). Tris(acetylacetonato)cobalt (7.1 mg, 2.0x10 mmol) and (+)-NORPHOS (13.8 mg, 3.0 x 10 mmol) are dissolved in 1 ml of THF under dry nitrogen, using standard Schlenk techniques. Norbomadiene (1.0 mL, 10.0 mmol) and 10 mmol of phenylacetylene or 1-hexyne are added. The reaction is started by addition of 5 mL of a IM solution of diethylaluminum chloride in hexane. The reaction mixture is kept at 35 °C for 4 h. Then 5 mL of isopropanol are added and the volatile components are removed in vacuum. The oily residue is distilled at 80 °C in high vacuum in a Kugelrohr apparatus. Chemical yield >99% enantiomeric excess 98.4-99.6% for (+)-4-phenyldeltacyclene and 97.6-98.0% for (+)-4-n-butyldeltacyclene. 

Supercritical water has the potential to be an interesting solvent system for organotransition metal systems. An example of this potential is found with the complex (7r- cp)Co(CO)2, which in organic solvents catalyzes the cyclotrimerization of hexyne-1, phenylacetylene, and butyne-2. At I40°C in aqueous media these reactions show poor selectivity to benzenes, but at 374°C in supercritical water the selectivity is again high (139). 

Pentyne and 1-hexyne are hydrogenated with [Ti(Cp)2(CO)2] to 1-pentene and 1-hexene, respectively, but phenylacetylene gives ethylbenzene. Reduced compounds of [Ti(Cp)2Cl2] with Na, Mg, Ca, sodium naphthalenide, or butyllithium catalyze the hydrogenation of a variety of alkynes to alkenes. 

A successful study of non-phosphine iridium complexes Ir", Ir , and Ir e. g., IrX(cod)2 [60], IrH2(triso)(SiMePh2)2 [61, 62], Ir(triso)(coe)2 (coe = cyclooctene triso = tris(diphenyloxophosphoranyl)methanide), Ir(triso)(C2H4)2 [61], has demonstrated effective hydrosilylation of alkenes and alkynes. Iridium phosphine complexes, e. g., Ir(C=CPh)(CO)2PCy2 [63] and IrCl(CO)(PPh3)2 [64], are also found to be active for hydrosilylation of phenylacetylene and 1-hexyne. 

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