Vinylcopper reagents

Because the vinylzinc and vinylcadmium reagents can be prepared directly from the vinyl halides (I, Br) with zinc or cadmium metal, this route avoids cross coupling processes and provides a one-pot in situ preparation of perfluo-rovinylcopper compounds Table 7 shows examples of this method of preparation of vinylcopper reagents from the indicated cadmium or zinc reagent [145]... 

Table 7. Preparation of Fluorinated Vinylcopper Reagents via Exchange of Cu(I) Halides with Fluorine-Containing Vinybinc or Cadmium Compounds [145]...

The reaction has been incorporated into a synthetic approach to enediynes [77]. Structural and mechanistic studies by Oehlschlager established the reversibility of these stannylcupration reactions [25cj. Although the resultant vinylcopper reagents were thermodynamically favored, crossover experiments found facile ligand exchange processes. Efforts to control the regiochemistry of the addition were met... 

Alkynyl(phenyl)iodonium Tosylates Preparation and Stereospecific Coupling with Vinylcopper Reagents. Formation of Conjugated Enynes P. J. Stang and T. Kitamura, Department of Chemistry University of Utah, Salt Lake City, UT 84112... 

Vinylcopper reagents, 207 Vinylcopper reagents-Magnesium(II) halide, 207... 

Although there are several exceptions, perfluorinated vinylzinc reagents react only slowly with allyl or acyl halides. Transmetallation of the vinyl zinc reagents to copper(I) halides provides high yields of vinylcopper reagents... 

E)-1,3-Enynes.2 These salts couple with vinylcopper reagents to give (E)-l,3-enynes in yields of 46-94%. 

The reaction was applied to the formation of arylcopper used for homocoupling and coupling reactions, which have already been described in Section IV.B.2. In addition, it was established that the simple use of copper(I) salts in polar solvents permitted the transmetallation from tin to copper. The transient vinylcopper reagent was subjected to various intramolecular reactions such as coupling with vinyl halides , addition to a, /S-unsaturated ketones , to a, /3-unsaturated esters and addition to a, /3-alkynic esters . In addition to copper(I) halides, the reaction can be mediated by copper(I) cyanide and... 

Vinylcopper reagents react with a wide variety of electrophilic reagents such as halogens, alkyl halides, allylic halides, acid chlorides, epoxides, a,(3-unsaturated ketones, and a,p-acetylenic esters with complete retention of the double bond stereochemistry. To enhance the reactivity of vinylcopper intermediates toward carbon electrophiles, the coupling is often carried out in the presence of activators such as HMPT, DMPU, and/or P(OEt)3 (triethylphosphite). Some representative examples of stereospecific... 

V-Silylated vinylcopper reagents are acylated with acid chlorides followed by palladium-catalyzed 1,5-sigmatropic rearrangement to form silyloxy dienes in moderate yield (equation 57)." ... 

The preparation of a,p-unsaturated ketones by direct acylation of vinylcopper reagents has proven more problematic, since lithium cuprates do add to the product enones. Better results are obtained with the less reactive monovinyl copper compounds in the presence of a palladium catalyst. Alkynic ketones have been prepared by a variation of the Stephens-Castro coupling. ... 

As seen in Scheme 1.14, exceptions to this are when benzyl [50], allylmagnesium chloride [51], vinylaluminum [52, 53], or vinylcopper reagents are used as nucleophiles [54]. 

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