Alkynyl-aryl coupling

The transition metal-catalysed coupling reaction of aryl halides with alkynes (alkynylation of aryl halides) is frequently also considered as a Heck reaction [68, 108-111], Polymers containing arylacetylene and diarylacetylene units in the backbone have been obtained by the self-coupling of ethynylaryl halides [scheme (3)] and the cross-coupling of aromatic dihalides with acetylene [scheme (6)] or diethynylbenzenes [scheme (7)] [112-121]. The majority of 

The reactivity of the aryl halide decreases in the halide order I Br, with chlorides failing to react. The reactivity of substituted aryl halides increases upon going from electron-donating substituents through unsubstituted aryl halides to electron-withdrawing substituents. Both reactivity patterns of Arl ArBr and activation of aryl halides with electron-withdrawing substituents follow the general reactivity of aryl halides in Pd(0) oxidative addition reactions [3], 

The Pd(PPh3)2 complex (PdL2) has two vacant coordination sites and easily undergoes a Cu(I)-promoted oxidative addition with aryl halide (Ar-X) to generate a Pd(II) complex. This is followed by the substitution of the halide 

In an analogous way, various poly(arylene alkynylene)s were obtained [120,134]. 

It should be noted that functionalised diacetylene monomers have also been used for coupling reactions with haloarenes. By reacting diacetylene-substituted p-aminoanilines [135] and diethynyl(methyl)( -octyl)silane [136] with diiodoarenes, polyamides and polysilanes have been prepared, respectively. 

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Figure 8.3 Schematic presentation of the mechanism for the aryl-alkynyl coupling reaction...

In addition to aryl alkynyl coupling reactions involving dihaloarenes and acetylenes or dialkynylarenes which lead to poly(arylene acetylene)s, it is worth noting that these polymers have also been obtained by the Pd(0)-catalysed heteropolycondensation of dialkoxy-substituted dibromoarenes with bis(tribu-tylstannyl)acetylenes [122]. 

Iodobenzyl 2-butynyl ethers undergo a Pd-mediated cyclisation with terminal alkynes to give lf/-[2]benzopyrans. The absence of a Cu(I) co-catalyst allows an intramolecular 6-exo-dig cyclisation to compete successfully with an intermolecular Sonogashira aryl-alkynyl coupling <02T9007>. 

Aryl-Alkynyl Coupling (Sonogashira Reaction) Reaction Conditions and Catalysts... 

Scheme 20 Aryl-alkynyl couplings employing alanes...

Alkenylboranes (R2C=CHBZ2 Z — various groups) couple in high yields with vinylic, alkynyl, aryl, benzylic, and allylic halides in the presence of tetra-kis(triphenylphosphine)palladium, Pd(PPh3)4, and a base to give R C CHR. 9-Alkyl-9-BBN compounds (p. 1013) also couple with vinylic and aryl halides " as well as with a-halo ketones, nitriles, and esters.Aryl halides couple with ArB(IR2 ) species with a palladium catalyst. ... 

Whereas Ullmann chemistry is limited to the coupling of aryl halides, a variety of species including aryl-, alkynyl-, alkenyl-, and alkylcopper species can be produced which are highly reactive toward other substrates. 

R = alkenyl, aryl, allyl, benzyl, propargyl R = alkenyl, aryl, alkynyl, alkyl, benzyl, allyl The Negishi Coupling was the first reaction that allowed the preparation of unsymmetrical biaryls in good yields. The versatile nickel- or palladium-catalyzed coupling of organozinc compounds... 

Aryl-AIkyne Coupling Reactions Alkynyl-de-halogenation, and so on Arl + RC=CCu... 

Palladium-catalyzed cross-coupling involving alkynylmetals and related alkynyl nucleophiles alkynyl-aryl, alkynyl-alkenyl, and alkynyl-alkynyl coupling... 

Subsequent studies have shown that alkenylzirconium derivatives generated in situ by hydrozirconation [46] of alkynes also undergo Pd- or Ni-catalyzed cross-coupling. As observed with alkenylalanes, Ni catalysts are generally satisfactory in the cases of alkenyl-aryl coupling [47] (Scheme 1-12), whereas Pd catalysts are more selective and distinctly superior to Ni catalysts in alkenyl-alkenyl and alkenyl-alkynyl coupling [48] (Scheme 1-13). 

Hydrometallation-cross-coupling and carbometallation-cross-coupling tandem protocols and other alkenyl-aryl, alkenyl-alkenyl, and alkenyl-alkynyl coupling reactions double metal catalysis... 

Molander, G. A., Katona, B. W., Machrouhi, F. Development of the Suzuki-Miyaura Cross-Coupling Reaction Use of Air-Stable Potassium Alkynyltrifluoroborates in Aryl Alkynylations. J. Org. Chem. 2002, 67, 8416-8423. 

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