Organocopper species

Michael additions [112] and other reactions typical of organocopper species can also be performed witli silylcoppet reagents such as TBDMSCu, prepared by Sn/Cu exchange [113] between Me- SnSiMeyifBu) and BuiHi)CuLi-LiCN iHi = 2-tbienyl) iScbeme 2.53) [113, 114]. 

Tridachiahydropyrone belongs to the family of marine polypropionates [69]. Efforts towards its total synthesis have recently led to a revision of the structure with the new proposal 2-147 [70]. The construction of the highly substituted cyclohex-enone moiety 2-146 which could be incorporated into this natural product [71] has been described by Perkins and coworkers (Scheme 2.33) [70, 72]. The conjugate addition/ Dieckmann-type cydization utilizing organocopper species as Michael donors afforded the enantiopure 2-145 in 68% yield. A further methylation of the (3-ketoester moiety in 2-145 followed by an elimination led to the desired cydohex-enone 2-146. 

The stoichiometric reaction of organolithium or Grignard reagents with copper halides allows direct formation of organocopper species(103). 

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. 

To date, hundreds of organocopper species have been isolated and characterized. It is beyond the scope of this chapter to discuss the synthesis and structural characterization of these compounds in detail [29]. Here, general structural features, especially those associated with the reactivity of organocopper compounds, are discussed and illustrated by representative examples. 

In this chapter, we will emphasize these recent developments, especially those that allow the preparation of organocopper species not accessible through the standard procedures involving organolithiums as precursors and their use in reactions with organic electrophiles. 

An elegant application of the homologation reaction was reported by Knochel and coworkers23. Reactions of organocopper species 43 with (iodomethyl)zinc iodide (40)... 

Good success has been reported with BF3-Et20. The combination of an organocopper species and BF3-Et20 gave a new complex,64 RCuBF3, which was far superior to RCu in its reactivity profile, and in many instances was also superior to R2CuLi (equation 26).5 There are many other examples of Lewis acid activation in the literature, with the details discussed in Volume 1, Chapter 1.12 and Volume 4, Chapter 1.3. 

The reaction of allyl halides with organocopper species usually gives regiochemical mixture of direct and S 2 attack. Exceptions to this trend are 3,3-disubstituted 1-bro-moalkenes, which give reliable direct substitution with lower-order cuprates or RCu organocopper reagents. This fact has been put to use in the synthesis of several prenelated... 

Recently, the direct transformation of allyl- 206272 and aryl tellurides 209273 into the corresponding organocopper species 207 and 210 by tellurium-copper exchange was described. The resulting allyl 207 or aryl cuprates 210 were captured by coupling with vinyl triflates 208272 or by 1,4-addition to enones 211,273 respectively (Scheme 112). 

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