Vinylcopper compounds

Few comparisons have been made among the relative stabilities of other classes of organocopper compounds. Generally, for simple derivatives, the order of decreasing stability is RC=CCu > Aryl-Cu > Alkyl-Cu. For vinylcopper compounds, 2-butenylcopper is more stable than propenylcopper 294). The higher homologs of methylcopper and lithium dimethylcuprate are less stable (69, 276, 297). 

The thermal decomposition of aryl- and vinylcopper compounds is an alternative method of obtaining dimeric products from organocopper compounds. Both methods have been used extensively by Kauffmann and co-workers 153-164). Thermal decomposition of organocopper compounds of the type ZN=C(R)—CHRCu affords suitable precursors for a variety of 1,4-diketones. Thermal decomposition is not applicable to all organocopper compounds (see Section III,B,3). Various oxidations and dimerizations are listed in Table V. 

Cuprates of the type Li CuR + i, where > 1, react with the carbonyl group of propynoate esters rather than give the conjugate addition product 61). Extension of the reaction of propynoate esters to vinylcopper compounds and allylcopper compounds affords a stereospecific synthesis of 1,3- and 1,4- dienes, respectively 64, 205). 

Organocopper compounds react slowly with nitriles or not at all 124, 233). Only a low yield of benzanilide was obtained from the reaction between phenylcopper and phenyl isocyanate 124). Isocyanate insertion reactions with vinylcopper compounds in HMPT in the presence of P(0C2H5)3 afford acrylamides 225a). 

In the presence of lithium acetylide, a vinylcopper compound reacts with oxiranes to give homoallyl alcohols (Eq. 266). ° ... 

Normant. J.E, Cahiez. G.. Chuit, C., and Villieras, J., Reactivity of vinylcopper compounds. Apphcation to the stereospecific synthesis of substituted allyhc alcohols. Tetrahedron Lett., 14, 2407, 1973. 

Synthesis of dienes [1, 169, before references], Tetrahydrofurane solutions of vinylmagnesium halides are readily accessible from vinyl halides by the method of Normant.19 Kauffmann and Sahm20 found that when a THF solution of the vinyl-magnesium compound (1) is treated at —60° to —40° under nitrogen with a suspension of cuprous chloride an intensely green or red solution is obtained which presumably contains a vinylcopper compound. When the mixture is warmed to... 

Vinyl halides. The method of Normant et al. (6, 270) for preparation of vinylcopper compounds can be used to obtain vinyl halides. Reaction of 1 with iodine gives vinyl iodides directly, but this reaction when extended to Bf2 or CI2 gives mainly dimers. The desired vinyl chlorides and bromides canTte obtained with NCS or NBS in fair to good yields. The replacement occurs with retention of initial stereochemistry. The American group also stresses the importance of the purity of the copper salt and uses House s cuprous bromide complex with dimethyl sulfide (6, 270). 

Dimerization of aryl- and vinylcopper compounds is selective and hence synthetically useful (Reich, 1923 Gilman and Kirby, 1929 Hashimoto and Nakano, 1966 Nilsson and Wennerstrom, 1969 Seitz and Madl, 1972). A non-free radical mechanism has been advanced for the reaction of penta-fluorophenylcopper and o-trifluoromethylphenylcopper tetramers (Cairncross et al., 1971) and m-trifluoromethylphenylcopper octamer (Cairncross and Sheppard, 1971). These reactions proceed on the metal cluster, and the Cu(I)-Cu(0) cluster compound is, in fact, isolable. 

Vinyllithium [917-57-7] can be formed direcdy from vinyl chloride by means of a lithium [7439-93-2] dispersion containing 2 wt % sodium [7440-23-5] at 0—10°C. This compound is a reactive intermediate for the formation of vinyl alcohols from aldehydes, vinyl ketones from organic acids, vinyl sulfides from disulfides, and monosubstituted alkenes from organic halides. It can also be converted to vinylcopper [37616-22-1] or divinylcopper lithium [22903-99-7], which can then be used to introduce a vinyl group stereoselectively into a variety of a, P-unsaturated systems (26), or simply add a vinyl group to other a, P-unsaturated compounds to give y, 5-unsaturated compounds. Vinyllithium reagents can also be converted to secondary alcohols with trialkylb o r ane s. 

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]...

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 ... 

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. ... 

Vinylic bromides. Reaction of vinylcopper reagents (2) with bromine leads to products of oxidation (dienes). However, vinylic bromides can be prepared from (2) by a two-step procedure. For example, (3) undergoes copper-mercury exchange with retention of configuration on treatment with mercuric bromide (0.5 eq.) to give (4) in 74% yield. This compound is converted by bromine in... 

Vinylcopper complexes. Use of this highly pure form of CuBr results in improved yields of vinylcopper complexes (1) from 1-alkynes (equation I). The reagents 1 were used in a new synthesis of functionalized trisubstituted alkenes (2) by conjugate addition to a, -unsaturated carbonyl compounds (equjition II). The probable stereochemistry of 2 is shown. The reactions are condueted in a one-flask procedure. ... 

When vinylcopper or allylcopper compounds are allowed to react with a, -acetylenic esters, 1,3- and 1,4-dienes are synthesized stereospecifically (Naf and Degan, 1971 Corey et al., 1972). The reaction of CCLVI and lithium divinylcuprate gives the addition product (CCLVII) in a purely cis form in >90% yield. The latter is converted readily to the prostaglandin intermediate (CCLVIII). Vinylcopper may be a superior reagent for this purpose. 

Alkylcoppers, arylcoppers, allylcoppers and vinylcoppers, besides acetylene-coppers, are also able to be used as organocopper reagents. The reactions with organocopper compounds, besides acetylene coppers, are not called the Castro reaction. However, recently these reactions are noted as being highly selective [43-b9]. 

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