Internal arylacetylenes

The reaction of aryl halides 1 with alkynylcopper(I) 2 under reflux in pyridine to prepare internal arylacetylenes is known as the Stephens-Castro reaction [Eq. (1)] [2]. The reaction has proved to be particularly important in the synthesis of a wide range of tolan and heteroaromatic alkynes [3]. Vinyl and allenic halides can also be used and several reviews... 

Acetylenic monomers also appeared to undergo polymerisation with conventional olefin metathesis catalysts. This relates to monosubstituted highly branched alkylacetylenes and arylacetylenes as well as disubstituted acetylenes (internal alkynes) [16-18], It has been demonstrated that acetylene itself may also be polymerised using olefin metathesis catalysts [19,20]. The polymerisation of alkynes [scheme (2)] involves a metathesis reaction [scheme (5) of Chapter 2] analogously to that of cycloolefins [21] ... 

I2 DMSO, " MeRe03/H202, " as well as by electrooxida-A ruthenium complex with a small amount of trifluoroacetic acid converts internal alkynes to the a-diketone. Ozone generally oxidizes triple-bond compounds to carboxyhc acids (19-9), but a-diketones are sometimes obtained instead. Selenium dioxide (Se02) with a small amount of H2SO4 oxidizes alkynes to a-diketones as well as arylacetylenes to a-keto acids (ArC=CH ArCOCOOH). " ... 

Biphenylene end groups were found to react at 350-400 °C with internal 1,2-di-arylacetylene group to form phenanthrene crosslink [89]. 

The Pauson-Khand reaction is the formation of cyclopentenones 486 by the action of dicobalt octacarbonyl on an alkyne, followed by an alkene. The process involves the intermediacy of cobalt complexes 485 (equation 53). (For reviews, see References 302 and 303.) Terminal alkynes, including acetylene and arylacetylenes, give better yields than internal acetylenes. An example of an intramolecular Pauson-Khand reaction is the conversion of the enyne 487 into the cyclopentanocyclopentenone 488 ". ... 

A different source of arenesulphenyl cations has been reported by Montevecchi and coworkers . They showed that the BFs-promoted reaction of 4 -nitrobenzenesulphena-nilide (35) with aryl-substituted alkynes in poorly nucleophilic solvents such as chlorobenzene generally led to bissulphides (36) and sulphimides (37) in addition to diphenyl disulphide and 4-nitroaniline. In acetonitrile as solvent, products of capture of the thiirenium ion by the solvent were also observed (equation 22). The thiirenium ion from phenylacetylene reacted even with the poorly nucleophilic solvent chlorobenzene to ( )-PhSCH=CPhC6H4Cl. With alkyl-substituted alkynes in chlorobenzene as solvent, a small amount of ( )-2-fluorovinyl sulphide PhSC(R )=CF(R ) was also detected. The yield of this sulphide could be increased when the reaction was performed in the presence of tetrabutylammonium tetrafluoroborate. Terminal alkynes gave the corresponding 2-fluorovinyl sulphides in 35-55% and internal alkynes in 65-87% yield. The procedure was unsuccessful for di-tcrt-butylacetylene and gave low yields for arylacetylenes. In acetic acid as solvent the thiirenium ion was captured as ( )-PhSC(R )=CR (OAc). 

Under the same conditions, a range of primary, secondary, and tertiary alkylmag-nesium chlorides reacted efficiently with silyl- and arylacetylenes, while aliphatic alkynes and internal alkynes were unreactive (Scheme 10.95). 

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