Phenylacetylene synthesis

Petrova, O.V., L.N. Sobenina, LA. Ushakov et al. 2009. Reaction of acetophenone and benzylphenylketone oximes with phenylacetylene Synthesis of di- and triphenylpyr-roles. Arkivoc iv 14—20. 

The synthesis of 2-chloro-2,3,3-trifluorocyclobutyl acetate illustrates a general method of preparing cyclobutanes by heating chlorotrifluoroethylene, tetrafluoroethylene, and other highly fluorinated ethylenes with alkenes. The reaction has recently been reviewed.11 Chlorotrifluoroethylene has been shown to form cyclobutanes in this way with acrylonitrile,6 vinylidene chloride,3 phenylacetylene,7 and methyl propiolate.3 A far greater number of cyclobutanes have been prepared from tetrafluoroethylene and alkenes 4,11 when tetrafluoroethylene is used, care must be exercised because of the danger of explosion. The fluorinated cyclobutanes can be converted to a variety of cyclobutanes, cyclobutenes, and butadienes. 

Other examples of [2C+2S+1C0] cycloaddition reactions have been described by Herndon et al. by the use of chromium cyclopropyl(methoxy)carbenes. These complexes react with alkynes releasing ethene and forming cyclopenta-dienone derivatives, which evolve to cyclopentenone derivatives in the presence of chromium(O) and water [122] (Scheme 76). This reaction has been extended to intramolecular processes and also to the synthesis of some natural products [123]. These authors have also described another process involving a formal [2C+2S+1C0] cycloaddition reaction. Thus, the reaction of methyl and cyclo-propylcarbene complexes with phenylacetylene derivatives does not afford the expected benzannulated products, and several regioisomers of cyclopentenone derivatives are the only products isolated [124] (Scheme 76). 

Monomers contained terminal phenylacetylenes protected with trimethyl-silyl groups and aryl iodides masked as N,hT-dialkyltriazenes. A typical PAM synthesis involved three basic transformations (Scheme 12) ... 

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. 

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. 

Although acetylenic bonds are more reactive than C=C bonds, the reactions are often initiated by AIBN or UV radiation. Baldwin and Barden119 have used the latter method to treat a doubly labelled phenylacetylene with triphenyltin deuteride (Scheme 19). The addition of the triphenyltin deuteride was both regiospecific and gave a stereochemically pure product. A five-step synthesis (Scheme 20) converted this product into an optically pure trideuterophenylcyclopropane, which was used to study the thermal stereomutations that these compounds undergo. 

The robustness and excellent turnover numbers of platinum complexes with terminal alkynes have made it the catalyst of choice for the synthesis of polymers and other macromolecular architechtures. Alkyne hydrosilylation with platinum has also served as a key element in the synthesis of dendrimers. Sequential reaction of an alkyne with HSiMeCl2 and lithiated phenylacetylene afforded the branching unit of a dendrimer synthesis which has been used to afford a large variety of structures at high generation.44,4411 441 ... 

The Sonogashira reaction is of considerable value in heterocyclic synthesis. It has been conducted on the pyrazine ring of quinoxaline and the resulting alkynyl- and dialkynyl-quinoxalines were subsequently utilized to synthesize condensed quinoxalines [52-55], Ames et al. prepared unsymmetrical diynes from 2,3-dichloroquinoxalines. Thus, condensation of 2-chloroquinoxaline (93) with an excess of phenylacetylene furnished 2-phenylethynylquinoxaline (94). Displacement of the chloride with the amine also occurred when the condensation was carried out in the presence of diethylamine. Treatment of 94 with a large excess of aqueous dimethylamine led to ketone 95 that exists predominantly in the intramolecularly hydrogen-bonded enol form 96. 

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. 

Carreira and co-workers developed a highly efficient enantioselective addition of terminal alkynes to aldehydes giving propargyl alcohols by the mediation of zinc tri-flate and N-methylephedrine [17]. This reaction serves as a convenient and powerful synthetic route to a wide variety of enantioenriched allenes via propargyl alcohols. Dieter and Yu applied this alkynylation to the asymmetric synthesis of allenes (Scheme 4.12) [18]. Reaction of phenylacetylene with isobutyraldehyde afforded the propargyl alcohol in 80% yield with 99% ee, which was mesylated to 49 in quantitative yield. Reaction of 49 with the cyanocuprate 50 afforded the desired allene 51 with 83% ee. 

An important procedure for the synthesis of cyclopentenones is the so-called Pauson-Khand reaction, which constitutes a formal [2 + 2 + 1] cycloaddition of an alkene, an alkyne, and carbon monoxide. Due to the increase in structural diversity of the available starting materials, the reaction has become an attractive target for scientific investigations [1-8]. The first successful example was reported by Pauson, Khand et al [9] in 1973 for the conversion of norbornene with the phenylacetylene-hexacarbonyldicobalt complex to give the corresponding cyclopentenone in 45% yield (Eq. 1). 

Few examples of the preparation of six-membered heteroaromatic compounds using Fischer-type carbene complexes have been reported [224,251,381]. One intriguing pyridine synthesis, reported by de Meijere, is sketched in Figure 2.35. In this sequence a (2-aminovinyl)carbene complex first rearranges to yield a complexed 1 -azadiene, which undergoes intermolecular Diels-Alder reaction with phenylacetylene. Elimination of ethanol from the initially formed adduct leads to the final pyridine. 

Zhang JS, Moore JS, Xu ZF, Aguirre RA (1992) J Am Chem Soc 114 2273-2274 Nanoarchitectures 1. Controlled synthesis of phenylacetylene sequences... 

Another problem with this method of synthesis is that unsymmetrical acetylenes can, and usually do, give two isomeric triazoles (Scheme 2). The sterically less hindered isomer is by no means always the major product In addition to phenylacetylene, for example, the 5-phenyl-triazole often predominates in the product mixture. 

Although a two-step synthesis of l,l -(l,3-phenylene)bis-(3-phenyl-2-propyn-l-one) (1,3-PPPO) has been reported [8], we found that 1,3-PPPO could also be prepared from a one-step route, starting from iso-phthaloyl chloride and phenylacetylene, employ-... 

Scheme 16 Synthesis of optically active poly(phenylacetylene) from optically active phenylacetylenes [109]...

Unlike in the case of the preparation of indoles and benzofuranes, the synthesis of benzothiophenes from o-ethynyl-thiophenols is not known. A close analogy was reported by Larock, where phenylacetylene was coupled with 2-iodothioanisole. Ring closure of the formed o-ethynyl-sulfide was initiated by the addition of different electrophiles. The reaction led to the formation of the benzothiophene core bearing the electrophile in the... 

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