Copper chloride with enolates

Reaction of the lithium enolate 2 with prochiral aldehydes at low temperature proceeds with little selectivity, producing all four possible diastereomers 3, 4, 5, and 6 in similar amounts50. Transmetalation of the lithium enolate by treatment with three equivalents of diethylaluminum chloride or with one equivalent of copper cyanide generates the corresponding cthylaluminum and copper enolates which react at — 100°C with prochiral aldehydes to produce selectively diastereomers 1 and 2, respectively50. The reactivity of tin enolates of iron- propanoyl complexes has not been described. 

In contrast, transmetalation of the lithium enolate at —40 C by treatment with one equivalent of copper cyanide generated a species 10b (M = Cu ) that reacted with acetaldehyde to selectively provide a 25 75 mixture of diastereomers 11 and 12 (R = CH3) which are separable by chromatography on alumina. Other diastereomers were not observed. Similar transmetalation of 10a (M = Li0) with excess diethylaluminum chloride, followed by reaction with acetaldehyde, produced a mixture of the same two diastereomers, but with a reversed ratio (80 20). Similar results were obtained upon aldol additions to other aldehydes (see the following table)49. 

Chiral carboxyamides derived from acid chlorides and A-chiral cA-aminoindanol can be protonated and Li Cu transmetallated to generate copper enolates which react with A-lithium derivative of A-Boc-O-tosylhydroxylamine (LiBTOC) 31 to give a-A-Boc amino carboxamides in high yields and enantiomeric excess (Scheme 38) . The chiral auxiliary can be removed by acidic hydrolysis to obtain the a-aminocarboxylic acid. 

Yield.—66% theoretical (10 gms.). Colourless crystals insoluble in water M.P. 61° gives a deep violet coloration with ferric chloride and a bluish-green crystalline precipitate of copper benzoyl acetone with alcoholic copper acetate. This shows the compound to be tautomeric, a little of the enol form being present at ordinary temperatures. The acidity of the hydroxyl group in the enol form is not so marked as it is in the case of the hydroxymethylene compounds nevertheless, the metallic salts of benzoyl acetone and such di-ketones are remarkably stable, and on account of their great crystallising power have been used for the determination of the valency and atomic weight of the rare elements. They are also of importance in the modern theory of co-ordination. (C., 1900,1., 588 B., 34, 2584.)... 

House and Fischer (38) have found that lithium dimethyl cuprate reacts with enone 108 and yields a mixture of trans and cis 3,5-dimethyl-cyclohexanones 109 and 110 in a 98 2 ratio. Similar results were observed by Allinger and Riew (39) using methylmagnesium iodide in the presence of copper(I) chloride. In another case, Heathcock and co-workers (AO) observed the exclusive formation of the trans isomer V[2 from enone 111 no cis isomer was detected. Thus, the preferred mode of approach by cuprate reagent is also 76 + 78 which leads to a chair-like enolate ion. 

With this end in view, phenyldimcthylsilyl tri-n-butylstannane was added under the influence of zero-valent palladium compound with high regioselectivity and in excellent yield to the acetylene 386 to give the metallated olefin 387 (Scheme 56). The vinyl lithium carbanion 388 generated therefrom, was then converted by reaction with cerium(lll) chloride into an equilibrium mixture (1 1) of the cerium salts 389 and 390 respectively. However, the 1,2-addition of 389 to the caibonyl of 391, which in principle would have eventually led to ( )-pretazettine, did not occur due to steric reasons — instead, only deprotonation of 391 was observed. On the other hand, 390 did function as a suitable nucleophile to provide the olefinic product 392. Exposure of 392 to copper(II) triflate induced its transformation via the nine membered enol (Scheme 55) to the requisite C-silyl hydroindole 393. On treatment with tetrafluoroboric acid diethyl ether complex in dichloromethane, compound 393 suffered... 

In ammoniacal solutions of copper salts, the oxidation products are likely to contain nitrogen thus, hexoses give oxalic acid, imidazoles, hydrogen cyanide, and urea. Kinetic studies have been reported for the reaction of Cu(II) in the presence of ammonia with maltose, lactose, melibiose, and cellobiose.190 For the oxidation by tetraamminecopper(II) in ammoniacal and buffered media the rate of reaction is first order in disaccharide concentration, order one-half in ammonia concentration, but it is independent of Cu(II) concentration. The reaction rate is decreased by the addition of ammonium chloride, because of the common ion effect. These kinetics suggested mechanisms involving an intermediate enediolate ion, with the rate of reaction being equal to the rate of enolization.191 A similar mechanism has been proposed for the oxidation of D-fructose by a copper-pyridine complex in an excess of pyridine.192... 

Apart from copper(I)-mediated reactions, few studies of the treatment of vinyliodonium salts with carbanions have appeared. The vinylations of the 2-phenyl- and 2- -hexyl-l,3-indandionate ions shown in equations 222 and 223 are the only reported examples of vinyliodonium-enolate reactions known to this author26,126. ( ,)-l-Dichloroiodo-2-chloroethene has been employed with aryl- and heteroarvllithium reagents for the synthesis of symmetrical diaryliodonium salts (equation 224)149,150. These transformations are thought to occur via the sequential displacement of both chloride ions with ArLi to give diaryl (/ -chlorovinyl)iodanes which then decompose with loss of acetylene (equation 225). That aryl(/ -chlorovinyl)iodonium chlorides are viable intermediates in such reactions has been shown by the conversion of ( )-(/ chlorovinyl)phenyliodonium chloride to diaryliodonium salts with 2-naphthyl- and 2-thienyllithium (equation 226)149,150. 

Copper(l) chloride in combination with tributyltin hydride shows unique character as an initiator of certain radical reactions. Hydrostannation of a,/3-unsaturated ketones with Bu3SnH is initiated by CuCl and the resulting tin enolates react with aldehydes under the influence of CuCl as a Lewis acid catalyst (Equation (81))/... 

Compounds with acidic hydrogen atoms react rapidly with cuprates. Phenylacetylene has been mentioned as one example (223). Another is diethyl phenylmalonate (144), which on addition to lithium dimethylcuprate gave a rapid evolution of methane and the formation of a methyl-copper-like precipitate which did not redissolve. Subsequent to the addition of benzoyl chloride and the customary work-up, only acetophenone and the phenylmalonate were isolated. The reaction may be summarized by Eq. (23). The failure to isolate the acylated product may be ascribed to the formation of the enolate, (II). 

A variety of methods are available for the halogenadon of aldehydes and ketones, and rely on the ease of enolization of such compounds. Copper(ID chloride or bromit in ethyl acetate at reflux have been shown to be effecdve reagents and rely on the promotion of enolization by the copper ion prior to the transfer of halogen. Since these conditions tend to favor the thermodynamic enol, unsymmetrical ketones preferentially halogenate at the more highly substituted a-carbon atom. Similar selectivity is observed with NBS. 0.11... 

Enol silyl ethers can lead to a-chloro ketones on treatment with anhydrous copper(II) chloride in DMF or iron(lll) chloride in acetonitrile (equation 13, Table 1). The chlorination of (36 equation 14) proceeds through a cation radical intermediate formed by an electron-transfer process with metal halides. 

The Michael addition of organometallic nucleophiles to enones in the presence of copper(I) salts produces enolates which on treatment with phenylselenenyl bromide give a-seleno ketones. For example, the reaction of the zirconium enolate of 15 with a mixture of phenylselenenyl bromide and diphenyl diselenide affords a mixture of diastereomeric (2R)- and (2V)-phenylse-leno)cyclopentanones 16 in 50% and 31 % isolated yield, respectively12. The analogous reaction with phenylselenenyl chloride gives only the tram-isomer in 27% yield formation of the cw-product is not observed12. 

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