Coupling of organocopper reagents

Castro-Stephens reaction Heck alkynylation Sonogashira alkynylating 

The Pd-catalyzed cross-coupling of terminal alkynes with aryl and alkenyl halides in the presence of Cu(I) as co-catalyst to give arylalkynes and enynes is known as the Sonogashira coupling (first time reported by Kenkichi Sonogashira et ah). Triethylamine or diethylamine is used as a solvent. 

The most used catalyst in this reaction is Cl2Pd(PPh3)2-CuI in Et2NH or Pd(PPh3)4-CuI in R2NH or R3N. For example, arylacetylenes were prepared by the Pd-catalyzed reaction of arylbromides with terminal alkynes in the presence of Cul in triethylamine (Et3N) base 

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All types of organocopper reagents couple readily with acid halides (Table XI), affording an alternative synthesis of ketones. Posner and... 

RCu CN) Bu)JLi. The complex /i-BuiNCu(CN)i (1) is prepared from CuCN and m-Bu4NCN (1 equiv.). This new class of cuprate reagents was introduced to effect coupling of the vinyllithium 2 with the iodide 3, which proceeds in low yield with a variety of organocopper reagents. However, the cuprate prepared from 2 and I equiv. of 1 reacts with 3 to form the desired coupling product in 69% yield. 

Use of organocopper reagents offers a very efficient method for coupling of two different carbon moieties. Since copper is less electropositive than lithium and magnesium, the C-Cu bond is less polarized than the C-Li and C-Mg bonds. This difference produces three useful changes in reactivity ... 

Halodiazinones undergo palladium-catalysed couplings with boronic acids and stannanes, but the reactions appear to be less consistent than with other systems. Temporary protection as silyl derivatives," or the use of additives such as silver oxide are beneficial in some cases, but it is often preferable to carry out transformations on alkoxydiazines, followed by hydrolysis. Direct coupling with organocopper reagents has also been described." ... 

Cross-coupling with Organocopper Reagents. HexasUylbi-cyclo[2.2.2]octan-l-yl copper, prepared from tbe treatment of hexasilylbicyclo[2.2.2]octan-l-yl lithium with copper(T) iodide in THF, reacts with (iodoethynyl)trimethylsilane (eq 6) in the presence of pyridine to afford the alkynyl-substituted polysilacage compound. ... 

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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