Cuprate mixed

The cuprates / Ba2Cu307 a with the orthorhombic (nearly tetragonal) R 123-type structure exist for R = Y and all 4f elements with the exception of Ce and Tb. For 0 < S < 0.6 they are cuprate-mixed-valence high-7"c superconductors, with the exception... 

Mixed cuprates. Mixed cuprates from this copper reagent are useful because of high solubility in THF and because (CH3)aCC=CCu is an expensive reagent. They are prepared by reaction of 1 and RLi in THF at — 78°. 

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... 

The optically active iodide 153 (Scheme 43) can be conveniently prepared from commercially available methyl (S)-(+)-3-hydroxy-2-methylpropionate (154) (see Scheme 41). At this stage of the synthesis, our plan called for the conversion of 153 to a nucleophilic organometallic species, with the hope that the latter would combine with epoxide 152. As matters transpired, we found that the mixed higher order cuprate reagent derived from 153 reacts in the desired and expected way with epoxide 152, affording alcohol 180 in 88% yield this regioselective union creates the C12-C13 bond of rapamycin. 

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. 

In these reactions one equivalent of chiral azaenolate remains unused. This can be overcome when a mixed azaenol cuprate 9 is employed with an acetylide as nontransferable ligand or when a mixed azaenol dimethylzincate 10 is used. Higher diastereoselectivities are achieved with zincates than with copper azaenolates and with (li ,2S )-2-methoxy-1,2-diphenylethanamine as auxiliary231. 

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... 

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