Organocopper complexes alkynes

Alkynylcoppers constitute a class of compounds relevant to several synthetic organic reactions,47 where they have been proposed as key intermediates. The interest in this area has supposed that the number of structurally characterized alkynylcopper complexes has considerably expanded in the last few years. The most common route toward alkynylcoppers is based on the reaction of a terminal alkyne with a copper source, either a salt or an organocopper compound (Equations (8) and (9)). 

When the CuBr-SMe2 complex is used in preparing the organocopper reagent, and Me2S is a cosolvent in the addition, higher yields may be achieved. Under such conditions even the otherwise unreactive methylcopper adds to terminal alkynes to generate 2-methyl-susbtituted alkenylcopper derivatives.520... 

Formation of metal-carbon bonds by addition of an organometallic reagent to an unsaturated compound or a diazonium compound is a little-used method in organocopper chemistry. Various alkylcopper reagents, (RCu + MgXg or LiX), add to acetylene or the alkynes, RC=CH, in a cis manner in ether or ether-pentane at low temperatures (223). A 7T-complex is a probable intermediate. The vinylcopper addition product obtained is dependent on the nature of the alkyne, being sensitive to electronic effects in the latter ... 

Transmetalation from Zr to Cu is a highly beneficial process as it combines the ease of preparation of organozirconocenes from alkenes and alkynes with the wide scope of organocopper reagents in organic synthesis. Schwartz and coworkers were first to demonstrate transmetalation to Cu in their report on the reductive dimerization of alkenylzirconocenes [94]. Virgili et al. used this transformation to prepare dialkoxy-1,3-butadienes [95]. The copper-mediated coupling of alkenylzirconocene 85 and phenethynyl bromide was reported to yield 86 [96] (Scheme 19). The latter two reactions can also be mediated by ox-ovanadium complexes [97]. 

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