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Phenylacetylene, reduction

Tandem cyclization/3-substitution can be achieved starting with o-(trifluoro-acetamido)phenylacetylenes. Cyclization and coupling with cycloalkenyl trif-lates can be done with Pd(PPh3)4 as the catalyst[9]. The Pd presumably cycles between the (0) and (II) oxidation levels by oxidative addition with the triflate and the reductive elimination which completes the 3-alkenylation. The N-protecting group is removed by solvolysis under the reaction conditions, 3-Aryl groups can also be introduced using aryl iodides[9]. [Pg.23]

A simple-minded picture suggests that the CC K bonds in aUcynes and alkenes ought to be similar. Are they Consider the thermodynamics of reduction of phenylacetylene to first give styrene and then phenylethane. (The energy for H2 is given at right.)... [Pg.115]

It should be noted that the selective reduction of phenylacetylene and diphenylacetylene to either the ds-alkene or the alkane was achieved using LiAlH4 in the presence of FeCk or NiCk as a catalyst [90, 91]. However, deuterolytic workup of the reaction mixtures gave deuterium incorporations <26%, indicating that these reagent systems are not well suited for the synthesis of vinyl- or alkylaluminum compounds from alkynes. [Pg.68]

After formation of Pd(0) from the Pd(II) precursor, oxidative addition of the P-H bond could give a hydride complex. Insertion of the alkyne into either the Pd-P or Pd-H bond, followed by reductive eUmination, gives the product Consistent with this proposal, treatment of Pt(PEt3)3 with PH(0)(0Et)2 gave the P-H oxidative addition product 14, which reacted with phenylacetylene to give primarily (>99 1) the Markovnikov alkenylphosphonate (Scheme 5-18, Eq. 2). [Pg.154]

Independent studies of the reduction of C=C and C=C bonds indicate that the latter is kinetically favored. Thus, in the absence of phenylacetylene, the rate of hydrogenation of styrene to ethylbenzene is about one order of magnitude faster than those for C=C bond reduction, indicating that the origin of the selectivity cannot be kinetic. The styryl compound represents a thermodynamic sink that causes virtually all the osmium present in solution to be tied up in this form, and therefore the kinetically unfavorable pathway becomes essentially the only one available in the presence of alkyne.31... [Pg.52]

Competitive reduction tests for cyclohexanone styrene, under transfer conditions, show preferential reduction of cyclohexanone however, under hydrogenation conditions the styrene is reduced exclusively.99 It is worth mentioning that the OsH2(r)2-H2)(CO)(P Pr3)2 precatalyst, formed by addition of NaBH4 to OsHCl (CO)(P Pr3)2, rapidly reduces phenylacetylene to styrene, under transfer conditions, but the reaction rate falls progressively due to the formation of Os(C=CPh)2 (CO)(P Pr3)2.72 As previously mentioned, an alkynyl-dihydrogen intermediate... [Pg.54]

Catalytic studies and kinetic investigations of rhodium nanoparticles embedded in PVP in the hydrogenation of phenylacetylene were performed by Choukroun and Chaudret [90]. Nanoparticles of rhodium were used as heterogeneous catalysts (solventless conditions) at 60 °C under a hydrogen pressure of 7 bar with a [catalyst]/[substrate] ratio of 3800. Total hydrogenation to ethylbenzene was observed after 6 h of reaction, giving rise to a TOF of 630 h 1. The kinetics of the hydrogenation was found to be zero-order with respect to the al-kyne compound, while the reduction of styrene to ethylbenzene depended on the concentration of phenylacetylene still present in solution. Additional experi-... [Pg.239]

Phenylacetylene, oxidative coupling to diphenyldiacetylene, 45, 39 partial reduction to styrene using palladium catalyst, 46, 90 reaction with sodium hypobromite to yield phenylbromocthyne, 45, 86 Phenylacetyl fluoride, 46, 6... [Pg.79]

Akita and Ohta disclosed one of the earliest Sonogashira reactions of chloropyrazines and their A-oxides [24, 25]. The union of 2-chloro-3,6-dimethylpyrazine (23) and phenylacetylene led to 2,5-dimethyl-3-phenylethynylpyrazine (29). Subsequent Lindlar reduction of adduct 29 then delivered (Z)-2,5-dimethyl-3-styrylpyrazine (30), a natural product isolated from mandibular gland secretion of the Argentine ants, Iridomyrmex humilis. [Pg.359]

This section presents the result of the catalytic performances in the case of phenylacetylene hydrogenation reaction. The catalytic evaluation was performed in a classical well-stirred stainless steel reactor operating in batch mode under constant H2 pressure (10 bar) at 17°C using n-heptane as the solvent. As mentioned in Section 13.2.2, no modification of the particle size distribution has been observed by transmission electron microscopy before or after reduction of colloidal oxide particles. [Pg.280]

Computational and catalytic studies of the hydrosilylation of terminal alkynes have been very recently reported, with the use of [ Ir( r-Cl)(Cl)(Cp ) 2] catalyst to afford highly stereoselectively P-Z-vinylsilanes with high yields (>90%) [35]. B-isomers can be also found among the products, due to subsequent Z —> E isomerization under the conditions employed. The catalytic cycle is based on an lr(lll)-lr(V) oxidahve addition and direct reductive elimination of the P-Z-vinylsilane. Other iridium complexes have been found to be active in the hydrosilylation of phenylacetylene and 1-alkynes for example, when phenylacetylene is used as a substrate, dehydrogenative silylation products are also formed (see Scheme 14.5 and Table 14.3). [Pg.350]

A second factor from which the solvent effect stems is associated with the insertion process. The reaction of species 6 with phenylacetylene revealed that the insertion took place into the H-Rh bond (Scheme 24). Although isolation of species 10 was not possible due to its high reactivity, 2D NMR techniques confirmed the structure. In CD2CI2, a polar solvent, the process took place smoothly even at room temperature to generate 10 (and 11 8 through reductive elimination from 10). However, the process was sluggish in toluene and more than 93% of 6 remained unchanged even after 24 h. [Pg.40]

Phenylacetylenes (3 mol) react with Te02 (1 mol) and excess of lithium halide in refluxing HOAc to produce 3-halobenzotellurophenes via the addition of a Te(IV) acetate halide to the triple bond, cychzation (probably by loss of HOAc) and reduction of the Te(IV) cyclic product to 3-halobenzotellurophene by an excess of the phenylacetylene. Owing to isolation facihties, the product is converted into the crystalhne dichlorides that is reduced to the benzotellurophenes. °... [Pg.292]

C yields a polymer with 90% cis content polymerization at 100°C yields a polymer with >90% trans content. Polyacetylene, doped with an oxidant or a reductant, showed promise as a polymeric semiconductor [Chien, 1984], That promise was not realized because of the oxidative instability of polyacetylene and emergence of cheaper and more stable polymer systems (Sec. 2-14j). Various substituted acetylenes such as phenylacetylene have also been studied [Kanki et al., 2002 Misumi et al., 2000],... [Pg.684]

Furane derivatives were also prepared by the carbonylation of acetylene derivatives. Phenylacetylene was converted to the furanone derivative shown in 3.35. under reductive conditions, while in the presence of oxygen 2-phenylmaleic anhydride was isolated as the main product.43... [Pg.42]

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... [Pg.345]

Acetylene can be made to react with aryl iodides in the presence of [PdCl2(PPh3)2] and Cul as catalyst (equation 180) 631 The potential intermediate, phenylacetylene, was not observed. (E) - 2-Bromostyrene and 2-bromopyridine also underwent the reaction. The initial reduction of palladium(II) to palladium(O) is believed to involve the coupling of two moles of acetylene. The precise mechanism is not known, but the reaction is thought to proceed according to Scheme 68. [Pg.302]


See other pages where Phenylacetylene, reduction is mentioned: [Pg.891]    [Pg.65]    [Pg.65]    [Pg.246]    [Pg.32]    [Pg.51]    [Pg.353]    [Pg.547]    [Pg.66]    [Pg.436]    [Pg.88]    [Pg.26]    [Pg.26]    [Pg.50]    [Pg.319]    [Pg.168]    [Pg.1182]    [Pg.811]    [Pg.683]    [Pg.891]    [Pg.244]   
See also in sourсe #XX -- [ Pg.49 , Pg.179 ]




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