Cyanocuprates higher-order

It appeared that [t-BuCu(CN)li(OEt)2] exists in the solid state as a dimer [t-BuCu(CN)Ii(OEt)2]2. Two anionic t-BuCu(CN) units, -with almost linear geom- 

NMR investigations [129, 132, 133], EXAFS and XANES studies [134-136], and theoretical calculations [127, 137, 138] performed on higher-order cyanocuprates strongly suggested that the cyanide anion was not bound to copper in these R2Cu(CN)Li2 species. Additional evidence was provided by the first X-ray crystal structure determinations of hi er-order cyanocuprates ((C,sH4CH2NMe2-2)2 Cu(CN)Li2] [139] (Eig. 1.34) and [(tBu)2Cu(CN)li2] [130] (Fig. 1.35). 

The molecular structure of the first compound comprises a polymeric chain, consisting of alternating [(C6H4CH2NMe2 2)2Cu] anionic and [Ii2(CN)(THF)4] cationic units. In the cationic unit, two lithium atoms are end-on bridged by the cyanide group, and two additional THF molecules are coordinated to each lithium atom. The fourth coordination site is occupied by the nitrc en atom of the adjacent (dimethylamino)methylphenyl group of the [(C6H4CH2NMe2-2)2Cu] anionic unit. 

On the basis of molecular wei t determinations by cryoscopy in THF and conductivity measurements, it was concluded that the polymeric chain breaks up in solution to form smaller aggregates, probably gieing rise to solvent-separated 

The structure of [t-Bu2Cu(CN)Li2] in the solid state consists of isolated [t-Bu2Cu] anionic units and [Li2CN(THF)2(PMDTA)2] cationic units (Fig. 1.35). 

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A further improvement in the cuprate-based methodology for producing PGs utilizes a one-pot procedure (203). The CO-chain precursor (67) was first functionalized with zirconocene chloride hydride ia THF. The vinyl zirconium iatermediate was transmetalated direcdy by treatment with two equivalents of / -butyUithium or methyUithium at —30 to —70° C. Sequential addition of copper cyanide and methyUithium eUcited the /V situ generation of the higher order cyanocuprate which was then reacted with the protected enone to give the PG. 

An important type of mixed cuprate is prepared from a 2 1 ratio of an alkyllithium and CuCN.11 Called higher-order cyanocuprates, their composition is R2CuCNLi2 in THF solution, but it is thought that most of the molecules are probably present as dimers. The cyanide does not seem to be bound directly to the copper, but rather to the lithium cations.12 The dimers most likely adopt an eight-membered ring motif.13... 

Hydroxy stannanes can be prepared by cleavage of epoxides with BusSnLi or cleavage of epoxy stannanes with organocuprates (equation 33)72. The two methods are stere-ochemically complementary. The higher order cyanocuprate, Bu3Sn(Bu)Cu(CN)Li2, also affords /1-hydroxy stannanes by reaction with epoxides54. 

A higher-order cyanocuprate, R2Cu(CN)Li2, reacts with a,P-unsaturated acylzirconocene chlorides at — 78 °C in THF to afford saturated ketones without giving a Michael-type product (Scheme 5.39). Treatment of the reaction mixture with D20 gives the [Pg.174]

Scheme 5.39. Reactions with higher-order cyanocuprate.

A large variety of cuprates are known nowadays. They include heteroleptic derivatives R(Y)CuM (Y = alkynyl, halide, amido, alkoxide, thiolato, phosphide M = Li or Mg), and have found widespread application in organic chemistry. Their syntheses and applications are discussed in the other chapters of this book. In addition, compounds in which the copper to lithium (or magnesium) ratio differs from 1 1 are also known examples are R3CuLi2 and the so-called higher order cyanocuprates introduced by Lipshutz et al. [99]. 

The importance of cyanocuprates as a synthetic tool in organic chemistry is well established. Depending on the amount of organolithium reagent LiR (one or two equivalents) added to CuCN, two different type of cyanocuprates are formed, with stoichiometries of RCu(CN)Li and R2Cu(CN)Li2, respectively [122] (Scheme 1.23). In order to distinguish between these two different types of cyanocuprates, the term higher-order cyanocuprates was introduced by Lipshutz et. al. for the second type of cyanocuprate, and the term lower-order cyanocuprate consequently... 

Another highlight of these additions was a systematic investigation of the use of alkylseleno- and alkyltelluro groups as non-transferable ligands of alkyl higher-order cyanocuprates [(RY)Cu(CN)R Li2, Y=Se, Te] in addition to enones. The following example is illustrative. 

Conjugate addition of higher-order cyanocuprates to enone, followed by O-functionalization... 

The etiolate intermediate, generated by the addition of higher-order cyanocuprates to enones, has been trapped with several electrophiles. Thus the addition of trimethylsilyl chloride, diethyl or diphenyl phosphorochloridate and iV-phenyltrifluoro methane-sulphonamide affords the corresponding vinyl silyl ethers, vinyl phosphates and vinyltri-flates. " ... 

One of the subunits of the natural product (-)-macrolactin A, a strong anti-viral agent, has been synthesized as shown in the following scheme, involving the hydrotelluration of a enyne (a), and the opening of an epoxide with a vinylic higher-order cyanocuprate (b). ... 

Mixed Higher Order Cyanocuprate-lnduced Epoxide Openings ... 

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