4-Arylacetylenes

Parameters of IR spectra (in solutions, films, or KBr) of acetylenylpyrazoles are close to those in the arylacetylene series. The values of the characteristic frequencies of the stretching vibrations of a disubstituted triple bond are in the... 

Few 1 -benzothiophene-S-oxides 218 were obtained in moderate yields by treatment of 1-arylacetylenes 219 with sulfur dioxide and benzene in the presence of antimony pentafluoride250 (equation 127). A series of cyclic sulphoxides have been prepared by hydrolysis of the corresponding alkoxy sulphonium salts 220251-254 (equation 128). Syn-sulphoxide 221 was obtained in a low yield (15-20%) in the reaction of the dianion of cyclooctatetraene 222 with thionyl chloride255 (equation 129). 

The novel highly substituted spiro[4.4]nonatrienes 98 and 99 are produced by a [3+2+2+2] cocyclization with participation of three alkyne molecules and the (2 -dimethylamino-2 -trimethylsilyl)ethenylcarbene complex 96 (Scheme 20). This transformation is the first one ever observed involving threefold insertion of an alkyne and was first reported in 1999 by de Meijere et al. [81]. The structure of the product was eventually determined by X-ray crystal structure analysis of the quaternary ammonium iodide prepared from the regioisomer 98 (Ar=Ph) with methyl iodide. Interestingly, these formal [3+2+2+2] cycloaddition products are formed only from terminal arylacetylenes. In a control experiment with the complex 96 13C-labeled at the carbene carbon, the 13C label was found only at the spiro carbon atom of the products 98 and 99 [42]. 

Scheme 20 Formation of highly substituted spiro [4.4]nonatrienes 98 and 99 from the (T-dimethylamino-2 -trimethylsilyl)ethenylcarbene complex 96 and arylacetylenes 97 [42,81]...

A microwave-assisted Cu-catalyzed Sonogashira-type protocol on aryl iodide substrates without the involvement of a palladium catalyst has also been published (Scheme 54) [71]. Reactions were executed using Cut and CS2CO3 in NMP at 195 °C. The application seems to be fairly limited since there are indications that only (hetero)arylacetylenes are suitable coupHng partners for this protocol. In addition, aryl bromides react more sluggishly than aryl iodides. Moreover, even on aryl iodides the reaction times required are on the order of hours. 

Unactivated aryl halides react with copper acetylides to give good yields of arylacetylenes Stephens-Castro coupling)P ... 

The relative rates of hydration of arylacetylenes in acetic acid water sulfuric acid to the corresponding acetophenones were investigated by Bott et al. (17), and they are listed in Table I. 

Once again, a large amount of diverse evidence indicates the intermediacy of a vinyl cation in electrophilic additions to arylacetylenes. As in the case of the hydration of alkynyl ethers and thioethers, the vinyl cation formed is especially stable because of resonance interaction and charge delocalization with the adjacent rr center of the aromatic system. 

Another important click reaction is the cycloaddition of azides. The addition of sodium azide to nitriles to give l//-tetrazoles is shown to proceed readily in water with zinc salts as catalysts (Eq. 11.71).122 The scope of the reaction is quite broad a variety of aromatic nitriles, activated and nonactivated alkyl nitriles, substituted vinyl nitriles, thiocyanates, and cyanamides have all been shown to be viable substrates for this reaction. The reaction of an arylacetylene with an azide in hot water gave 1,4-disubstituted 1,2,3-triazoles in high yields,123 while a similar reaction between a terminal aliphatic alkyne and an azide (except 111 - nitroazidobenzcnc) afforded a mixture of regioisomers with... 

Cyclotrimerization of arylacetylene was observed in the reaction of [PhC=CAg] with [(dppm)2Au2(MeCN)2]2+[BF4-]2 in dichloromethane. The products form an AusAg9 cluster containing 1,2,3-tri-phenylarene units aurated in the 4,5,6-positions.136... 

Palladium-catalyzed addition of the selenium-silicon bond of PhSe-SiMe3 to arylacetylenes proceeds in a regio- and stereoselective manner to afford (Z)-a-(phenylseleno)-/ -(trimethylsilyl)styrenes (Equation (123)).250 Aliphatic alkynes fails to undergo the addition reaction. Analogous addition of the Se-Ge bond to alkynes occurs under similar conditions. 

The palladium-catalyzed asymmetric hydrosilylation of styrenes has been applied to the catalytic asymmetric synthesis of l-aryl-l,2-diols from arylacetylenes (Scheme 6).46 Thus, ( )-l-aryl-2-(trichlorosilyl)ethenes, which are readily generated by platinum-catalyzed hydrosilylation of arylacetylenes, were treated with trichlorosilane and the palladium catalyst coordinated with MOP ligand 12f to give 1 -aryl-1,2-bis(silyl)ethanes, oxidation of which produced the enantiomerically enriched (95-98% ee) 1,2-diols. 

Ortiz de Montellano PR, Komives EA. Branchpoint for heme alkylation and metabolite formation in the oxidation of arylacetylenes by cytochrome P-450. J Biol Chem 1985 260(6) 3330-3336. 

Particularly significant results have been obtained in the oxidative carbonylation of simple and functionalized alkynes. Thus, the PdI2/KI-catalyzed oxidative carbonylation of simple alkyl- or arylacetylenes, as well as of propy-nyl alcohol and propynyl acetate, carried out in alcoholic solvents under mild conditions (15-25 atm of CO, 4-9 atm of air, 25-80 °C), led to the formation of maleic derivatives (together with small amounts of fumaric derivatives) and 5,5-dialkoxyfuran-2(5H)-ones, in high yields and with unprecedented catalytic efficiencies for this kind of reaction (up to ca. 4000 mol of product... 

The toxic potential of metabolic intermediates, of the carrier moiety, or of a fragment thereof, should never be neglected. For example, some problems may be associated with formaldehyde-releasing prodrugs such as N- and 0-[(acyloxy)methy 1] derivatives or Mannich bases. Similarly, arylacetylenes assayed as potential bioprecursors of anti-inflammatory arylacetic acids proved many years ago to be highly toxic due to the formation of an intermediate ketene. 

The versatility in the construction of dendritic macromolecules, and the unique advantages offered by a controlled step-wise approach, are perhaps best illustrated by the all hydrocarbon family of arylacetylenic dendrimers devel-... 

Fig. 4. Extended monomers, 27 and 28, used in construction of dendritic poly(arylacetylenics)...

Fig. 5. Chromophore labeled dendritic poly(arylacetylenic),30, for LED applications...

TetralkylteUnriiims, prepared in situ by the reaction of tellurium tetrachloride with 4 equiv of alkyllithiums, react with arylacetylenes to afford dialkyl tellurides A, alkylation products B, an alkene C and minor amounts of a vinyl telluride D. ... 

Toluene-p-sulfonyl azide adds to electron-deficient acetylenes and to phenylacetylene at 80°-100° over a period of several days. The azide adds much more readily to ynamines, - refiecting the electronic compatibility of these components. The triazoles so formed are labile and exist in equilibrium with open-chain diazo tautomers (Section IV, G) the adduct with ethoxyacetylene exists entirely in the diazo form. Other sulfonyl azides have been reacted with arylacetylenes, but yields of triazoles are generally poor. ... 

For the asymmetric 1,4-addition of alkenyl groups in aprotic media, alkenyl zirconium reagents can be used, which are generated by hydrozirconation of terminal alkynes (Figure 3.30). Under these conditions, alkenyl groups derived from alkylacetylenes are efficiently installed, but those from arylacetylenes are not as effective (entry 3). 

The authors proposed mechanism for dimerization involves initial formation of metal vinylidene complex 9 via 1,2-H-migration. A second molecule of arylacetylene acts as a dienophUe in a formal [4 + 2] Diels-Alder cycloaddition with 9. A subsequent... 

Scheme 9.2 Cyclodimerization of arylacetylenes with a rhodium porphyrin catalyst.

A series of 3-chloro-4-arylacetylenic pyridazines have been cyclized to the corresponding 5-aryl-furo(or pyrrolo or thia)[2,3-( ]pyridazinones <2006TL6125, 2006JMC3753>. 

The bromination with alkali hypobromite in aqueous solution gives good results with (hetero)arylacetylenes, enynes (RCH=CHOCH) and diynes (RC=CC=CH) all acetylenes that are more acidic than those acetylenes in the aliphadc or cycloaliphatic series with an isolated triple bond. For the conjugated systems the hypobromite method is superior to the reaction of metallated acetylenes with bromine. Various acetylenic alcohols are also brominated smoothly, which can be explained in part by their better solubility in water. Since in the case of primary and secondary ethynyl alcohols, oxidation of the alcohol can occur, the use of an excess of hypobromite should be avoided. The best procedure is drop wise additon of a small shot measure of hypobromite ro a mixture of alcohol and water. If the bromoalkynes to be prepared are not too volatile, small amounts of THF or dioxane may be added to effect a better solubility of the alkyne in the aqueous phase. Addition of a co-solvent may also be desired when the starting compound is a solid (e.g. ethynylcyclohexanol). 

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