Mixed cuprates

Posnet examined a series of hetetoatom mixed cuprates iXCu BuLi), which displayed a range of tliernial stabilities [X itempetatute at which reagent is stable for one bout) PhS PhO i-30 C), f-BuO i-50 C) [189], f-BuS and Et2N i -c-78... 

Betlz has subsequently developed aniido [195] and phosphido [195, 196] mixed cuprate reagents featuring increased reactivity and greater thernial stability A use-... 

Hie first example of a diital catbanionic residual ligand has recently been reported [238]. Chiral mixed cuprates generated from alkyilitliium reagents... 

Tlie recognition of tlie imporiance of duster structure has resulted in a new un-detstanding of tlie role of a dummy ligand (Y) in tlie diemistry of mixed cuprates MeCulYiLi [145], As sliown in Sclieme 10.15 for tlie case of Y = ahty nyl, tlie... 

It will be recalled that lactone-derived enol triflate 102 was expected to serve as a substrate for a Murai coupling37 with the mixed cuprate reagent derived from iodo ortho ester 103 (see Scheme 17c). If successful, this C-C bond forming process would accomplish the introduction of the remaining carbon atoms needed for the annulation of the seven-membered D-ring lactone. 

This reagent is perhaps best thought of as a higher-order mixed cuprate of the type (R3Si)2Cu(CN)Li2 (7). 

The procedure described here illustrates the preparation of mixed lithium arylhetero(alkyl)cuprate reagents and their reactions with carboxylic acid chlorides,4 These mixed cuprate reagents also react with a,a -dibromoketones,12 primary alkyl halides,4 and a,/3-unsaturated ketones,4 with selective transfer of only the alkyl group. 

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... 

Conjugate addition reactions involving organocopper intermediates can be made enantioselective by using chiral ligands.86 Several mixed cuprate reagents containing... 

Give the products expected from each of the following reactions involving mixed cuprate reagents. 

Conjugate addition to unsaturated esters.13 The mixed cuprate formed from butyllithium and copper(I) trimethylsilylacetylide, (CH3)3SiC=CCu, is more efficient than BuCu/BFj or Bu2CuLi for conjugate addition to a, p-unsaturated esters. Yields of the adduct are markedly improved by addition of CISi(CH3)3 (1.3 equiv.) to the reaction. 

Thienyl(cyano)copper lithium S Cu(CN)Li xhe reagent is obtained by reaction of thiophene with BuLi in THF at - 78° and then with CuCN at - 40°. The reagent is fairly stable and can be stored in THF at - 20° for about 2 months. It is inert, but is readily converted by addition of RLi or RMgX into a higher-order mixed cuprate, which is as efficient as the freshly prepared cuprate."1... 

The reaction of 1,2-allenyl ketones with organocuprates afforded /3,y-unsaturated enones. The reaction with mixed cuprates RR CuLi delivered, depending on the properties of R and R, two products 430 and 431 [192]. 

Tab. 3.6. Thermal stability of n- and t-Bu(heteroatom) cuprates in comparison to n-BuCu, n-Bu2CuLi, and homo mixed cuprates at 0 and 25 °C for 30 minutes, measured by quenching with PhCOCI after aging of the copper species [195a],...

The first example of a chiral carbanionic residual ligand has recently been reported [238]. Chiral mixed cuprates generated from alkyllithium reagents and cyclic a-sulfonimidoyl carbanions transfer alkyl ligands [such as n-Bu, Me, (CH2)30CH(Me)0Etj to cyclic enones with excellent enantioselectivities (77-99% ee). 

Thienyl vinyl tellurides are valuable reagents for the transfer of the vinyl group. By treatment with Bu2Cu(CN)Li2 they are converted in a single step into the mixed cuprate... 

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