Phenylacetylene oxidation

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... 

Scheme 4.9 Phenylketenyl radical formation by phenylacetylene oxidation.

As an application of maleate formation, the carbonylation of silylated 3-butyn-l-ol affords the 7-butyrolactone 539[482], Oxidative carbonylation is possible via mercuration of alkynes and subsequent Lransmetallation with Pd(II) under a CO atmosphere. For example, chloromercuration of propargyl alcohol and treatment with PdCF (1 equiv.) under 1 atm of CO in THF produced the /3-chlorobutenolide 540 in 96% yield[483]. Dimethyl phenylinale-ate is obtained by the reaction of phenylacetylene, CO, PdCU, and HgCl2 in MeOH[484,485]. 

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]. 

Styrene undergoes many reactions of an unsaturated compound, such as addition, and of an aromatic compound, such as substitution (2,8). It reacts with various oxidising agents to form styrene oxide, ben2aldehyde, benzoic acid, and other oxygenated compounds. It reacts with benzene on an acidic catalyst to form diphenylethane. Further dehydrogenation of styrene to phenylacetylene is unfavorable even at the high temperature of 600°C, but a concentration of about 50 ppm of phenylacetylene is usually seen in the commercial styrene product. 

The thermal or photolytic fragmentation of furazans to nitriles and nitrile Af-oxides has been reported (73JOC1054, 75JOC2880). The irradiation of dimethylfurazan (419) in the presence of cyclopentene, and benzofurazan (420) in the presence of dimethyl acety-lenedicarboxylate, gave isoxazoline (421) and isoxazole (422), respectively, in good yields. The thermolysis of acenaphtho[l,2-c]furazan (423) in the presence of phenylacetylene gave isoxazole (424) in 55% yield. 

Phenylacetylene gives 1-phenyI-l, l-difluoroethane on reaction with a large excess of hydrogen fluoride in ether at 0 C or, in better yield, in the gas phase over a mercuric oxide catalyst [/]. Allene affords 2,2-difluoropropane [/]... 

The additions of phenyl azide and phenylnitrile oxide to pentafluorophenyl-acetylene are also regiospecific [75, 7S] (equation 12). Interestingly, in the latter reaction, phenylacetylene gives regiochemistry that is opposite to that observed for pentafluorophenylacetylene [75]... 

In contrast to other furoxans, the cycloreversion of 3,4-dinitrofuroxan to nitro-formonitrile oxide was observed even at room temperature. The nitrile oxide could be trapped in situ with electron-deficient nitriles (Scheme 149) (95MC231). Attempts to obtain cyclo adducts with styrene, phenylacetylene, rran.s-stilbene, and cyclohexene failed. 

Oxidative polymerization of trans-bis-deprotected 79 under Hay coupling conditions [54] yielded, after end-capping with phenylacetylene, the high-melting and readily soluble oligomers 80a-e with the poly (triacetylene) backbone [87,106] (Scheme 8). Poly(triacetylene)s [PTAs,-(C=C-CR=CR-C=C) -] are the third class of linearly conjugated polymers with a non-aromatic allcarbon backbone in the progression which starts with polyacetylene [PA,... 

Hydroxy(tosyloxy)iodobenzene 2014 reacts with phenyltrimethylsilane 81 in boiling acetonitrile to give diphenyliodonium tosylate 2015 and trimethylsilanol 4 or HMDSO 7 [184, 185]. Likewise, treatment of 2,5-bis(trimethylsilyl)furan 2016 with 2014 in boiling acetonitrile/methanol affords 78% iodonium tosylate 2017 and trimethylsilanol 4 [185]. In the presence of Bp3-OEt2 iodosobenzene oxidizes allyl-trimethylsilanes such as 2018 to unsaturated aldehydes such as 2019 in 63% yield, with formation of iodobenzene and trimethylsilanol 4 [186]. Analogously, vinyltrimethylsilanes such as (Z)-l-trimethylsilyl-2-phenylethylene 2020 afford, via 2021, acetylenes such as phenylacetylene in 61% yield and iodobenzene and trimethylsilanol 4 [187] (Scheme 12.54). 

The complexes [Cu(NHC)(MeCN)][BF ], NHC = IPr, SIPr, IMes, catalyse the diboration of styrene with (Bcat) in high conversions (5 mol%, THF, rt or reflux). The (BcaO /styrene ratio has also an important effect on chemoselectivity (mono-versus di-substituted borylated species). Use of equimolecular ratios or excess of BCcat) results in the diborylated product, while higher alkene B(cat)j ratios lead selectively to mono-borylated species. Alkynes (phenylacetylene, diphenylacety-lene) are converted selectively (90-95%) to the c/x-di-borylated products under the same conditions. The mechanism of the reaction possibly involves a-bond metathetical reactions, but no oxidative addition at the copper. This mechanistic model was supported by DFT calculations [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). 

The side products of the reaction between benzoylnitromethane 279 and dipolarophiles (norbornene, styrene, and phenylacetylene) in the presence of l,4-diazabicyclo[2.2.2]octane (DABCO) were identified as furazan derivatives (Scheme 72). The evidence reported indicates that benzoylnitromethane gives the dibenzoylfuroxan as a key intermediate, which is the dimerization product of the nitrile oxide. The furoxan then undergoes addition to the dipolarophile, hydrolysis, and ring rearrangement to the final products (furazans and benzoic acid) <2006EJ03016>. 

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. 

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... 

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. 

A totally different route based on dehydrogenation of a saturated polymer precursor was introduced by Francois et al. [49] (Scheme 2.9). The method is based on anionic copolymerization of cyclohexadiene with styrene, followed by oxidation with chloranil. Due to possible coupling of two styrene (or two cyclohexadiene) molecules, a block copolymer, containing oligo(phenylene vinylene) units separated by oligo(phenylacetylene) and oligo(phenylene) blocks, is obtained. To the best of our knowledge, it was, so far, used only in the synthesis of phenyl-substituted PPV 10. 

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