Organocopper compounds vinylation

The relative reactivity of organocopper compounds in additions to 6 and 7 is as follows vinyl > aryl > isopropyl > ethyl > methyl. 

The consensus favors a transitory copper(III) intermediate in the reaction of a copper corapound with an alkyl or vinyl halide 37, 57, 65, 185, 297), although Tamura and Kochi consider such an intermediate unlikely for alkyl halides (276). Collman (57) has suggested that organocopper compounds are representative of a number of transition... 

Diorganocuprates couple readily with vinylic halides and have been employed in the synthesis of some natural products, e.g., fulvoplumieren and Cecropia juvenile hormone (26, 27, 62, 63). Copper-halogen exchange can occur simultaneously 174, 309). Successful coupling reactions of organocopper compounds with vinylic halides are listed in Table VIII. 

Ebert, G. W., RIeke, R. D. Preparation of aryl, alkynyl, and vinyl organocopper compounds by the oxidative addition of zerovalent copper to carbon-halogen bonds. J. Org. Chem. 1988, 53,4482-4488. 

In a study of the reactivity of organocopper compounds with a,/3>unsaturated aldehydes, allylic and acetylenic cuprates have been found to give selective 1,2-addition to afford allylic alcohols, in contrast to the predominant 1,4-addition observed with homoallylic, phenyl, and vinyl cuprates secondary alkyl cuprates give both types of addition product. 

This procedure illustrates a general method for the preparation of alkenes from the pal 1 adium(Q)-cata1yzed reaction of vinyl halides with organo-lithium compounds, which can be prepared by various methods, including direct regioselective lithiation of hydrocarbons. The method is simple and has been used to prepare a variety of alkenes stereoselectively. Similar stoichiometric organocopper reactions sometimes proceed in a nonstereoselective... 

An analogous mechanism was proposed for the conversion of the triflate 416 to the vinyl-, allyl- and allenyl-A2-cephems 448 in yields of 47-71% by the respective tributyltin compounds in the presence of cuprous chloride (Scheme 6.91) [176]. Accordingly, the cyclic allene 417 should be liberated from 416 in the first step. Then, the organocopper species would transfer a hydrocarbon group to the central allene carbon atom of 417, leading to an allyl anion derivative, which is protonated during the workup. These reactions of 416 and 443 indicate that the cyclic allenes 417 and 444 behave toward nucleophiles as 1,2-cyclohexadiene (6) (Schemes 6.11— 13) and its non-polar derivatives such as 215 (Scheme 6.51), 221 (Scheme 6.52), 311 (Scheme 6.67) and 333 (Schemes 6.71 and 6.73), that is, they interact with nucleophiles at the central carbon atom of the allene system exclusively. 

If the reaction was carried out in THF with R2CuMgX or [RCuBr]MgX as the or-ganometallic reagent, a vinylic compound was prepared upon protonation. The E Z ratio of the product depends strongly on the type of organocopper reagent used. The reaction may proceed via the attack of Cu on the central carbon atom of the allene moiety, followed by transfer of the R group from Cu to the terminal carbon atom [54]. 

This simplified view can explain stability trends and differences between various organocopper(I) compounds, as well as the influence of bulky or coordinating substituents ortho to the copper-carbon bond on the stability of arylcopper compounds. This interpretation of the copper-carbon bond can also be applied to the binding of sp (alkyl e.g., CH2SiMe3), sp (C=C-R) [40], and other sp (vinyl) groups [41, 42]. 

Organocopper reagents, 207 Organovanadium reagents, 219 By desilylation of vinylsilanes Tetrabutylammonium fluoride, 286 By desulfurization of vinyl sulfides and related sulfur compounds Sodium dithionite, 281 Elimination reactions By dehalogenation Dichlorobis(cyclopentadienyl)-titanium, 102... 

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