Dimerization phenylacetylene

The following chemicals were obtained from the Aldrich Chemical Company, Inc., and were used without further purification p-acetamidoben2enesulfonyl chloride, 97% acetone, 99.9+%, HPLC grade sodium azide, 99% ethyl acetoacetate, 99% triethylamine, 99% rhodium(ll) acetate dimer phenylacetylene, 98%. The following solvents were obtained from Fisher Scientific and were used without further purification toluene, certified A. C. S. ethyl ether (Solvent grade. Concentrated) petroleum ether, certified A. C. S. Dichloromethane was distilled from calcium hydride. 

Pd-catalyzed cross-coupling of aryl iodide 38 and terminal phenylacetylene 39 gave a dimer (e. g. 40) containing both trimethylsilyl-protected acetylene and aryltriazene moieties. 

FeCls whenever used). To confirm the formation of the ether intermediate a separate experiment was performed between dimeric ether and phenylacetylene, observing that the dimeric ether reacted smoothly with phenylacetylene in the presence of FeCl3-6H20 to produce the desired ketone in a similar yield ( 42%) to that obtained when starting from the benzylic alcohol. 

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],... 

Borst et al. <2005CEJ3631> conducted a study on the synthesis of strained bicyclic phosphirane and phosphirene iron-tetracarbonyl complexes (Scheme 11). It was shown that, depending on the ring size of the resulting heterocycle, electrophilic phosphinidene [Ri-PrNP=Fe(CO)4] could be trapped intramolecularly with both double and triple bonds (compounds 146-150). The phosphinidene addition was found to be reversible at room temperature and when using phenylacetylene as solvent, exchange between phenylacetylene and the phosphinidene group took place. Compound 151 was isolated as the dimer, compound 152. 

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 variety of palladium-catalyzed dimerizations of conjugated enynes and their additions to diynes and triynes gave rise to styrene and phenylacetylene derivatives, respectively. Inter alia, 1,2,4-cyclohexatrienes have been invoked as intermediates in these reactions [134], 5,6-Diphenyl-l,2,4-cyclohexatriene has been proposed as an intermediate in the rearrangement of 4,4-diphenylcyclohexa-2,5-dienylidene to o-ter-phenyl and its possible existence was supported by quantum-chemical calculations [135],... 

Cuprous cyanide was used as purchased from Aldrich Chemical Company, Inc. Trace amounts of copper(ll) may cause dimerization of the phenylacetylene. 

Attempts to turn this acetylene dimerization reachon into a catalyhc polymeriza-hon process have failed thus far. In the presence of excess phenylacetylene, the iridium(I) complex 23 activates another Caikynyi—H bond and hansforms, after a hydrogen shift, to the stable (vinyl)(alkynyl) iridium(III) system 27 (Equahon 12.10). 

Most of these catalytic systems are able to dimerize either aromatic alkynes, such as phenylacetylene derivatives, or aliphatic alkynes, such as trimethylsilylacetylene, tert-butylacetylene and benzylacetylene. The stereochemistry of the resulting enynes depends strongly on both the alkyne and the catalyst precursor. It is noteworthy that the vinylidene ruthenium complex RuCl(Cp )(PPh3)(=C=CHPh) catalyzes the dimerization of phenylacetylene and methylpropiolate with high stereoselectivity towards the ( )-enyne [65, 66], and that head-to-tail dimerization is scarcely favored with this catalyst. It was also shovm that the metathesis catalyst RuCl2(P-Cy3)2(=CHPh) reacted in refiuxing toluene with phenylacetylene to produce a... 

PET converts phenylacetylene to ot-phenylnaphthalene a 1,4-bifunctional dimer radical cation (96 +) is the key intermediate 1,6-cyclization, followed by a hydrogen or hydride shift generates the final product. ... 

The dimeric complex 74 reacts with phenylacetylene or ferrocenylacetylene to yield the tetrameric complexes 75a and 75b, respectively, according to equation 26. These complexes are stable in CDCI3 solution in the absence of air and can be characterized by H and NMR spectroscopies. The low solubility of 75a in unreactive organic solvents precludes detailed studies of the solution structure in reactive solvents it decomposes to a dimeric complex, 76, according to equation 27 3. j jjg association behavior of these complexes resembles that of analogous organolithium compounds - 303... 

Ollis, and Ramsden520 treated 99, 100 and 101 with neat EPP and obtained the pyrazole 103 and the phenylpropiolic ester dimer 104, but no 105. A comparative study was carried out with phenylacetylene. When 100 was heated with DM AD in dioxane, 25% of the pyrazole 106 was obtained. These authors have concluded that the cycloaddition of alkynes to isosydnones is analogous to that of sydnones but the reactions are slower and the cycloadducts are obtained in lower yields. 

The catalytic dimerization of alkynes has led to the development of a variety of catalysts by new combinations of transition metals and ligands, and to a better understanding of the processes and mechanism involved, leading to improvement of selectivity and scope. In Table 1 the most relevant catalysts are compared with regard to phenylacetylene dimerization. The nature of the terminal alkyne has also a marked effect on the outcome of this reaction. 

Table 1. Selectivity of phenylacetylene dimerization by some transition metal catalysts.

Mononuclear ruthenium complexes have become useful catalysts, not only because they can have high regio- and stereoselectivity but also because their catalyzed reactions rely on an elucidated mechanism. This true for the cis-dihydride (PP3)RuH2 complex, a catalyst precursor for the selective head-to-head dimerization of phenylacetylene to the corresponding (Z)-enyne, via bis(alkynyl) active spe-... 

Reports on ruthenium catalytic activity focus more on mechanistic consideration of the prototypical phenylacetylene dimerization than in establishing its synthetic applicability. It is not unusual that changing the alkyne substituents results in reversed selectivity (i.e. R = Ph or SiMe3 gave ( )- or (Z)- isomers, respectively) [27]. Competitive alkyne cyclotrimerization (R = COOMe) [27] or butatriene formation (R= CH2Ph, Bu) [10, 21] have occasionally been reported as possible drawbacks in enyne synthesis. The operating mechanism restricts the reaction to terminal alkynes. 

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