Cuprates involving

Vinyl cuprates.3 An attractive route to vinyl cuprates involves transmetalla-tion of vinylzirconates, available by hydrozirconation of 1-alkynes with the Schwartz reagent in THF at 25°. Transmetallation can be effected with CH3Li (3 equiv.)... 

Layered cuprates involving double fluorite layers... 

A number of alternative multi-step procedures for the synthesis of a-tert-alkyl ketones are known, none of which possess wide generality. A previous synthesis of 2-tert-penty1cyclopentanone involved reaction of N-1-cyclopentenylpyrrol 1 dine with 3-chloro-3-methy1-l-butyne and reduction of the resulting acetylene (overall yield 46 ). However, all other enamines tested afford much lower yields. Cuprate addition to unsaturated ketones may be useful in certain cases. Other indirect methods have been briefly reviewed. ... 

On tlie basis of tliis Lotidusioti and on NMR studies of Lomplexes of 17b witli Lewis adds, a transition state model to explain tlie observed sdectivity was proposed. Tliis involved initial Lomplexation of a cuprate litliium ion to tlie tliree different betetoatoms in tlie substrate, followed by fotniation of a d-E complexation... 

In acyclic propargylic systems, organocopper and -cuprate reagents react similarly to afford allenes. An overall anti-Sfl process is involved, probably via a copper(III) intermediate. Typical examples are shown in Table 3. 

Scheme 36). Interestingly, the higher order cuprate 206 underwent conjugate addition with only moderate selectivity. This is likely due to the intervention of an electron transfer pathway. Competing electron transfer reactions involving a-alkoxymetal reagents of this type have also been reported by Cohen [81]. 

The mechanism of conjugate addition reactions probably involves an initial complex between the cuprate and enone.51 The key intermediate for formation of the new carbon-carbon bond is an adduct formed between the enone and the organocopper reagent. The adduct is formulated as a Cu(III) species, which then undergoes reductive elimination. The lithium ion also plays a key role, presumably by Lewis acid coordination at the carbonyl oxygen.52 Solvent molecules also affect the reactivity of the complex.53 The mechanism can be outlined as occurring in three steps. 

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

Arylcopper intermediates can be generated from organolithium compounds, as in the preparation of cuprates.95 These compounds react with a second aryl halide to provide unsymmetrical biaryls in a reaction that is essentially a variant of the cuprate alkylation process discussed on p. 680. An alternative procedure involves generation of a mixed diarylcyanocuprate by sequential addition of two different aryllithium reagents to CuCN, which then undergo decomposition to biaryls on exposure to oxygen.96 The second addition must be carried out at very low temperature to prevent equilibration with the symmetrical diarylcyanocuprates. 

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

An alternative method to prepare (Mormyl esters uses different building blocks to assemble the 1,4-dicarbonyl system and is complementary in many cases.10 Base-catalyzed addition of nitromefhane to a, J-unsaturated esters, followed by a variation of the Nef reaction, provides y-dialkoxy-substituted esters. The scope of this sequence has not yet been explored. Another approach involves cuprate additions to norephedrine-derived 2-alkenyloxazolidines this process allows small-scale synthesis of several p-formyl esters in optically active form (ee up to 95%).11... 

A number of pyridazines have been prepared by standard condensations of enediones with hydrazine but a general synthesis of the intermediate enediones is notable. This involved iodine-copper exchange of an iodoenone 3, followed by reaction of the resulting cuprate with acid chlorides. However, only a few of these enediones were actually converted into pyridazines <06OL1941>. 

Dieter developed a flexible two step synthesis of substituted pyrroles involving initial Beak deprotonation of /ert-butoxycarbonyl (Boc) amines 36 followed by addition of CuX-2LiCl (X = -Cl, -CN) to afford a-aminoalkylcuprates. Such cuprates undergo conjugate addition reactions to a,(3-alkynyl ketones affording a,(3-enones 37, which upon treatment with PhOH/TMSCl undergo carbamate deprotection and intramolecular cyclization to afford the pyrroles 38 . 

An alternative route to allenyl stannanes involves organocuprate displacements on propargylic chlorides bearing an alkynyl PhsSn substituent (equation 39)79. Interestingly, transmetallation by attack of the cuprate on the tin substituent is not observed in these systems. A parallel strategy can be employed for allenylgermanes (equation 39)79. The... 

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