Homo-coupling of terminal alkynes

Oxidative homo-coupling of terminal alkynes using copper catalyst in the presence of oxygen. 

Oxidative homo-coupling of terminal alkynes mediated by stoichiometric (or often excess) Cu(OAc)2. A variant of the Glaser coupling leactioa... 

The homo-coupling of terminal alkynes is a frequent side reaction in Sonogashira and Heck-type alkynylation reaction. However, this reaction can be optimized to obtain Glaser-type products in good yields. The power of this reaction has been demonstrated in the synthesis of a wheel-like structure by Hoger and colleagues (Experimental Procedure below). ... 

Intermolecular palladium-catalyzed homo- and hetero-coupling of terminal alkynes is well documented, but rigorous mechanistic investigations of this oxidative coupling have not been reported. The proposed mechanisms revolve about (isomerization of) intermediate dialkynylpalladium(ii) complexes and subsequent reductive elimination. The catalytic cycle in the presence of iodine is shown in Scheme 6. 

Some of the most useful synthetic transformations of terminal alkynes involve intermolecular and intramolecular homo- and cross-coupling reactions between their. sp-carbon centers, leading to butadiyne or polyyne derivatives. The two most widely used and practical systems are (i) oxidative homocoupling reactions, i.e. Glaser and Eglington reactions and (ii) heterocoupling reactions, i.e. Chodkiewicz-Cadiot coupling of a terminal alkyne with a haloalkyne. 

Terminal alkynes react to form l-en-3-ynes in a process catalyzed by palladium acetate and tris(2,6-dimethoxyphenyl)phosphine. A number of functional groups such as internal alkenes, esters, and alcohols are tolerated, and good yields of homo- (eq 25) as well as hetero-coupled enynes (eq 26) are obtained. ... 

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