Glaser-type alkyne coupling

Whereas Glaser-type oxidative coupling opens efficient synthetic pathways toward symmetrical diynes, its performance in heterocoupling is poor. The latter may be accomplished by Cadiot-Chodkiewicz coupling of terminal alkynes with 1-haloalkynes (usually 1-bromoalkynes). The reaction is conducted in the presence of an amine and catalytic amounts of a copper(I) salt. Because, in contrast with the Glaser-type reactions described above, it follows a nonoxidative reaction mechanism, oxygen is not necessary - but needs often not to be excluded (Scheme 4) [9]. 

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). ... 

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