Cyanocuprates lower-order

As already noled, lower order cyanocuprates are more Su2 -selective reagents. On irealmenl widi acetale 163, however, a mixture of tlie iwo regioisomets was oblained fetilry 2) [81]. In addih on, y-alkylalion bad taken place witli ca. 2 596 loss ... 

Cyanocuprates constitute a class of organocopper compounds that finds applications in organic synthesis.234 They are prepared by the direct reaction of an organolithium reagent and CuCN, with two different types of compounds being prepared depending on the stoichiometry employed the 1 1 ratio leads to RCu(CN)Li compounds whereas the 2 1 mixture affords R2Gu(GN)Li2. The lower- order or 1 1 cyanocuprates usually display the Cu-C-N-Li... 

Lower order cyanocuprates RCu(CN)Li displayed again a different behavior although they usually do not react with acceptor-substituted enynes, the cyanocuprate tBuCu(CN)Li nevertheless underwent anti-Michael additions to 2-en-4-ynoates (e.g. 70) and nitriles affording allenes of type 73 (Scheme 2.26) [51]. Unfortunately, an adequate interpretation of the abnormal behavior of this particular cuprate is still lacking. 

So-called lower order cyanocuprates RCu(CN)Li do not generally react with acceptor-substituted enynes. An exception is the cuprate t-BuCu(CN)Li which undergoes anti-Michael additions with 2-cn-4-ynoates and nitriles (equation 61)151. The mechanistic aspects of this very unusual reaction are unknown radical intermediates and electron transfer steps have not been found. 

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... 

The solution structures of cyano-Gilman cuprates and lower-order cyanocuprates have been studied by cryoscopic measurements in THF [141]. The results of this study have in several cases shown ways to obtain useful single crystals of several higher- and lower-order cyanocuprates and consequently to determine their structures in the solid state. It appears that a number of these cyanocuprates retain their observed solid-state structure when dissolved in THF. 

Scheme 6.40. Influence of alkene geometry on stereoselectivity of allylic substitution of mesylates 189 and 192 with boron trifluoride-modified lower order cyanocuprate reagents.

The stereochemistry outcome of the above reaction, proceeding with inversion of the C3-C4 double bond geometry, is anomalons since it differs from the well-established retention of the geometry in the conpling reaction of (Z)-vinylic tellurides with higher- and lower-order cyanocuprates. ... 

The lower order (L.O.) cyanocuprate (2-Th)Cu(CN)Li has an excellent shelf life, thereby providing a highly stable precursor to higher order cuprates.9 Tetrahydrofuran solutions of this L.O. cuprate are available commercially (from Aldrich Chemical Company, Inc.), thus allowing further simplification of this procedure. 

Most of the recent developments in the vinyl halide reaction chemistry of lower-order cuprates are of zinc cyanocuprates (RCu(CN)ZnX)24. While only reacting with unfunc-... 

Silyl cuprates give high yields of acylsilanes with acid chlorides (equation 58)77. Both lower-order Gilman trimethylsilylcuprates and h.o. cyanocuprates accomplish the transformation. 

Acid chlorides also couple smoothly with lower-order zinc cyanocuprates (equation 59) to give ketones in high yields. Although most acid chloride substrates employed have been simple ones, alkenes, benzylic and alkyl chloride functional groups have been present in the acyl halide without incident25. 

Like their carbon counterparts, silylcuprates and stannylcuprates readily participate in SN2 -substitution reaction with allylic electrophiles.43,51 For example, <37z//-diastereoselective allylic substitution of the vinyl oxiranes 147 with the lower-order cyanocuprate (PhMe2Si)Cu(CN)Li cleanly affords the allylsilanes 148 (Scheme 38).106 Products of this type can be converted into the corresponding diols with retention of configuration by Tamao-Fleming oxidation 53,53a,53b,107... 

Higher order alkyl cyanocuprates containing MgBr as the counter-ion 214 couple efficiently with (Z)-vinylic tellurides to give the corresponding tellurium-free olefins with retention of the (Z)-stereochemistry 215.281 By using lower-order cyanocuprates 216, the coupling is efficient even with lithium as the counter-ion (Scheme 114).282... 

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