Alkynylation alkynyl-aryl coupling

Palladium catalysed alkynyl-aryl coupling preparation of mesitylacetylene27... 

Arylmetals can be coupled with alkenyl and alkynyl halides. In these cases, the reverse polarity affinity patterns, i.e., the alkenyl-aryl and alkynyl-aryl coupling reactions... 

Metals of intermediate electronegativities exhibited, in general, the highest catalytic activities in Pd-catalyzed cross-coupling, as observed first in alkynyl-aryl coupling reaction (Table 1 in Sect. IILl). 

Even in the alkynyl-aryl coupling where Zn, B, Sn, and Mg have been shown to be comparably satisfactory in less demanding cases, some clear-cut differences have been shown in more demanding cases (Scheme 5). This aspect is further discussed in Sect. III.2.8.2. Curiously, ethynylborates do not give the desired products in any detectable amount, even though higher alkynylborates react satisfactorily. 

These findings prompted us to systematically screen various metals in the Pd-catalyzed alkynyl-aryl coupling. Both alkynylmetals and aryl halides are readily and widely available. This study indicated that Zn, B, and Sn were the three most favorable metals, which were followed by Mg and Al, but that some other metals including Li, Hg, Si, and Zr essentially failed to give the desired products under... 

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. ... 

Stille reaction the palladium-catalyzed reaction of an aryl or vinyl halide with an organotin reagent, where one of the organic groups is alkynyl, aryl, or vinyl, to give a cross coupled product... 

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). 

Another noteworthy development is an asymmetric synthesis of chiral biaryls by a Pd-catalyzed enantioselective aryl-aryl coupling reaction of prochiral 2,6-bis(triflyloxy)biaryls [62], Using Cl2Pd[(53-Phephosl as a chiral catalyst, the first phenylation of l-[2,6-bis(triflyloxy)phenylJnaphthalene with PhMgBr proceeds in 85% ee. As might be expected, the minor enantiomer is the more reactive of the two in the second phenylation. This leads to a kinetic resolution, and the desired monophenylated enantiomer can be obtained in 93% ee. Similarly favorable enantioselective alkynylation results have also been reported [180]. 

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