Homo- and Cross-Coupling of Alkynes

Homo-dimerization of terminal alkynes is catalyzed by Pd complexes. Usually control of regio- and stereoselectivities is difficult and a mixture of isomers 234, 235 

Control of selectivities in cross-dimerization of two alkynes is more diffieult. Trost et al. carried out selective dimerization of 1-alkynes with aeceptor alkynes, possessing an EWG, using TDMPP [72], Furthermore, Trost and Meintosh succeeded in the selective cross-coupling of 1-alkyne 241 with unactivated alkyne 242, obtaining the coupled product 243 in 62% yield [73]. 

Yamamoto et al. reported a new and more complicated dimerization of diynes. Pd(PPh3)4-eatalyzed reaction of dodecadiyne (50) in the presence of AcOH afforded ( )-l,2-dialkenyl-1,2-dialkynylethylene 244 in 65% yield [74], 

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Homo- and cross-couplings of alkyne promoted by metallic catalysts are versatile reactions for carbon-carbon bond formation and have been utilized to synthesize functional hyperbranched polymers. 

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