Phenylethynyl halides

A study of the reaction of phenylethynyl halides with methoxide anion revealed a complex addition-elimination mechanism for this substitution. Such reactions require application of DMSO as a solvent and afford alkynyl ethers only in 42-46% yield. Reactions of phosphorylated chloroacetylenes 74 with alkoxide anions are even less selective and afford products of nucleophilic addition to the triple bond as major products. However, analogous reaction of 74 with phenoxide anion gives phenoxyacetylenes 75 in moderate yield (equation 46). ... 

Early studies concentrated mostly on phenylethynyl halides and were interpreted in terms of radical intermediates. Specific attempts to induce ionic photobehavior from the 1-halo-l-hexynes 209 in polar media, including the use of low temperature and viscous solvents, afforded almost exclusively radical-derived products. This is consistent with the high ionization potentials of 1-alkynyl radicals. 

Since it is known that halo(phenyl)acetylenes add oxidatively to Vaska s complex to give (7-phenylethynyl iridium(III) halides, 32112, the intervention of phenyliodonium iridium(III) and rhodium(III) intermediates, 33, in the alkynyliodonium reactions seems plausible. In any case, the production of cr-alkynyl complexes with alkynyl(phenyl)-iodonium triflates appears to be both more general and efficient21. 

Attempts to isolate 1-cyclopentadienyl-, 1-phenylethynyl-, and 1-alkyl-2,4,6-triphenyl-thiabenzenes by reaction of 9 with alkyllithiums or Grig-nard reagents have been unsuccessful and only IH- and/or 4//-thiopyrans have been obtained. However, a transient intense coloration of the reaction solutions has been taken as evidence that the primary nucleophilic attack is at the sulfur atom (62JA2090 71JOC791). Contrarily to aryllithi-ums, arylmagnesium halides do not allow the isolation of thiabenzenes but only of 2H- and 4//-thiopyran adducts (72JOC1718). 

The application of the ketone synthesis has continued. Phenylethynyl and vinylethynyl ketones have been synthesized by the reaction of appropriate acid halides with phenylethynylzinc chloride 521, 522) and vinyl-ethynylzinc chloride 552), respectively. 

Although many transition metal complexes containing T) -bonded substituted acetylides are known, few are available in more than moderate yields via conventional reactions of metal halides with an anionic aUcynyl compound of an alkali metal, magnesium, or copper(I) or hy dehydrohalogenation in a reaction between the metal halide and a 1-alkyne. More recently, reactions between many 1-alkynes and RuCl(l Ph3)2(Tj -CsHs) have been shown to give cationic vinylidene complexes, which are readily deprotonated to give the corresponding substituted Tj -acetylides. The synthesis of the phenylethynyl derivative is typical the intermediate phenylvinylidene complex is not isolated. 

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