A,<o-Diynes

Coupling reactions of non-conjugated a,o>diynes have been systematically classified by Tamao [17]. 

An jco-OT o-cyclisation of a,o -diynes promoted by bis(pyridyl)iodonium(i) tetrafluoroborate (IPy2BF4) has been described for the first time and is an excellent route for accessing a variety of sulfur-containing heterocycles when employing alkynyl sulfides (Scheme 49) <1998AGE3136>. 

Among partially intramolecular versions of this cocycloaddition, a,o>-diynes have been found to cycloadd only with low efficiency to isocyanates in the presence of CpCo precursors. In contrast, o>-iso-cyanatoalkynes react smoothly with silylated alkynes in the presence of CpCo(CO)2, giving high yields of products formed with excellent chemoselectivity and modest to excellent regioselectivity (equation 47). The regioselectivity is most likely controlled in a manner similar to that in equation (43). ... 

Anneiated benzenes.1 Vollhardt s cocyclization of bis(trimethylsilyl)ethyne with a.tu-diynes has been extended to several new partners. Thus a,trimethylsilyl)propyne and trimethylsilylalkynes. Examples are shown in equations (I) and (II). 

The cyclopolymerization of a,o)-diynes (equation 30) has been intensively studied by Choi and coworkers with a variety of dipropargyl compounds containing different substituents (31)266,278,281-288... 

When a,o>-diynes are oxidised in aqueous ethanolic solution by oxygen in the presence of copperfl) chloride and ammonium chloride... 

Takeuchi and coworkers reported an iridium-catalyzed cycloaddition of a,o -diynes and nitriles to give pyridines in 2012 [57]. With [Ir (cod)Cl]2/DPPF or BINAP as the catalytic system, pyridines were formed effectively (Scheme 3.24). A wide range of nitriles (aliphatic and aromatic nitriles) can be applied and reacted smoothly with Q ,a -diynes to give the pyridines. In the case of unsymmetrical diyne bearing two different internal alkyne moieties, high regioselectivity can be achieved which can be explained by the different reactivities of the a-position in iridacyclopentadiene. Terpyridine and quinquepyridine were prepared as well. [Ir(cod)Cl]2/chiral diphosphine catalyst can be applied to enantioselective synthesis. Kinetic resolution of the racemic... 

The influence of the positions of the geminal dimethyl groups in the formation of bis-gfem-dimethylcycloalkynes from oc,(o-dibromoalkanes and the disodium salts of a,(o-diynes was interpreted in terms of conformational effects/ ... 

Pd/Cu-catalyzed coupling of 150 with excess of the liberated pentamer 151 affords the polymer supported 17-mer. Directly heating the mixture of 150 and 151 causes a much lower yield, possibly due to decomposition of the a,with acid liberates the free 120-nm long 17-mer 152. ... 

Table 3.11 Some 2-oxopyridinophanes from a,

Acetylene and its derivatives are polymerized using suitable transition metal catalysts to give high-molecular-weight (MW) polymers (Scheme 1). The monomers include acetylene, mono- and disubstituted acetylenes, and a,carbon-carbon double bonds along the main chain and exhibit unique properties, such as metallic conductivity, that are not expected with vinyl polymers. 

As shown above, a,o)-diynes are reactive substrates in [2 + 2 + 2]-cycloaddition chemistry. However, a limitation of the use of a,o)-diynes is the presence of a secondary fiised-ring system in the arene product. A more flexible synthetic strategy that does not need the tether is desired. [2 + 2 + 2] Cycloaddition of monoynes is a challenging target in the synthesis of polysubstituted benzenes. However, selectivity is a drawback, and the development of a highly selective catalyst is desired. 

Bicyclo[3.3.0]octadienones, bicyclo[4.3.0]nonadienones, and bicyclo[5.3.0]deca-dienones but also cyclopentadienones with annulated 0-, S-, and IM-heterocycles are obtained in high yields from bis(trimethylsilyl) protected a,o)-diynes following the same approach (Scheme 4-4). ... 

Kase, K., Goswarmi, A., Ohtaki, K., Tanabe, E., Saino, N. and Okamoto, S. (2007) On-demand generation of an efficient catalyst for pyridine formation from unactivated nitriles and a,[Pg.260]

Polyenyne Oligomers Oligomeric a-o-Diynes Oligo(alkynes)... 

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