Electrophiles alkyne reactions with

Terminal alkynes with no electron-withdrawing group next to the acetylenic linkage when treated with enamines merely add across the double bonds of the enamines (9i). But electrophilic alkynes (those with an electron-withdrawing group next to the acetylenic linkage) undergo cycloaddition reactions with enamines. 

Alkynes undergo electrophilic addition reactions with hydrogen halides and bromine, but these reactions have limited synthetic utility. However, one reaction of alkynes that is commonly used in organic chemistry is hydration of the carbon-carbon triple bond to give a ketone, a transformation that is catalyzed by mercuric ion in the presence of sulfuric acid (Eq. 11.10). 

Oxazolium hydroxide, anhydro-5-hydroxy-aromaticity, 6, 184 cycloaddition reactions, 6, 209 dimerization, 6, 207 1,3-dipolar cycloaddition reactions with alkynes, 6, 210 electrophilic reactions, 6, 207 mesoionic reactions, 6, 188 reactions, 6, 206-211 synthesis, 6, 225-227... 

The chemistry of alkynes is dominated by electrophilic addition reactions, similar to those of alkenes. Alkynes react with HBr and HC1 to yield vinylic halides and with Br2 and Cl2 to yield 1,2-dihalides (vicinal dihalides). Alkynes can be hydrated by reaction with aqueous sulfuric acid in the presence of mercury(ll) catalyst. The reaction leads to an intermediate enol that immediately isomerizes to yield a ketone tautomer. Since the addition reaction occurs with Markovnikov regiochemistry, a methyl ketone is produced from a terminal alkyne. Alternatively, hydroboration/oxidation of a terminal alkyne yields an aldehyde. 

Alkynes react with electrophilic selenium reagents such as phenylselenenyl tosylate.155 The reaction occurs with anti stereoselectivity. Aryl-substituted alkynes are regioselective, but alkyl-substituted alkynes are not. 

Because of the slightly acidic nature of the sp C-H bonds, the reaction of metal acetylides with various electrophiles is one of the most general strategies in organic transformations.1 Traditionally, such reactions are carried out by using alkali metal acetylides which are air and water sensitive. On the other hand, there is much interest in developing transition-metal catalyzed terminal alkyne reactions involving soft and more stable C-M bonds as reaction intermediates, because many such reactions can tolerate water. 

The synthesized CPMV-alkyne 42 was subjected to the CuAAC reaction with 38. Due to the strong fluorescence of the cycloaddition product 43 as low as 0.5 nM, it could be detected without the interference of starting materials. TMV was initially subjected to an electrophilic substitution reaction at the ortho-position of the phenol ring of tyrosine-139 residues with diazonium salts to insert the alkyne functionality, giving derivative 44 [100]. The sequential CuAAC reaction was achieved with greatest efficiency yielding compound 45, and it was found that the TMV remained intact and stable throughout the reaction. 

Alkenes and alkynes react with sulfur dichloride (SC12), giving 2-chloroethyl(or vinyl)sulfenyl chlorides. The reaction is an electrophilic addition to the multiple bond, and consequently the possible intermediacy of thiiranes, or thiiranium ions analogous to bromonium ions, has been... 

Alternatively, l,3-dithiol-2-ones have been obtained by reacting di-isopropylxanthogen disulfide with unsaturated substrates, such as disubstituted alkynes R2C2, in the presence of AIBN (azoisobutyrylnitrile), a radical initiator.78 Finally, vinylene dithiocarbonates can be obtained by reacting mer-cury(II) acetate with the corresponding trithiocarbonates, generated by reaction of electrophilic alkynes with ethylene trithiocarbonate.79 Analogously,... 

The reactions of electrophilic alkynes, such as DMAD (dimethyl acetylene-dicarboxylate), with metal per- and poly-chalcogenido complexes have been exploited for the synthesis of homoleptic and heteroleptic 1,2-dithiolene,... 

The bisfunctionalization of alkynes by both C02 and another electrophile can also be achieved, as shown in Scheme 9.17,17a The titanium-carbon bond in the titanacycle complex 31, which was formed by reaction of C02 with the titanacyclopropene 30, can be substituted with various electrophiles. For example, its reaction with NBS or I2 afforded the synthetically useful vinyl bromide or iodide 32, respectively, while the reaction with D20 yielded the /3-deuterated a,/ -unsaturated carboxylic acid. When an aldehyde such as PhCHO was used as an electrophile, butenolide 33 was produced after acidic workup. 

Quaternary ammonium tribromides can also be produced in situ from the quaternary ammonium bromide, sodium hypochlorite and sodium bromide and can be used, for example, in electrophilic addition reactions reaction with alkenes and alkynes. 

Addition of 2 mol equivalents of T " to alkynes gave bis-perchlorates 40 [R = H, Me, Ph R = R = MeO (geometry not established)], which were explosive upon heating. The alkyne reactions were much slower than those with alkenes, and no reaction at all occurred with ethyl propiolate, from which it was concluded that all these reactions have the character of electrophilic addition to the unsaturated unit (79JOC915). 

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