Lithium enolates of acetaldehyde

Scheme 8.37 Use of the lithium enolate of acetaldehyde DMH in an epoxide ring-opening reaction.

A facile preparation of 4-(heptafluoropropyl)quinoline 53 occurred on treatment of ortho-(nonafluorobutyl)aniline with the lithium enolate of acetaldehyde <96TL(37)4655>. 

Wen and Grutzner used, among other NMR parameters, the QSC of the lithium enolate of acetaldehyde to deduce that it exists as tetramers of different solvation in THF and THF/n-hexane solvent systems . However, the most thorough study of Li QSC and the most interesting in the present context was reported by Jackman and coworkers in 1987167 -pjjg effects on the QSC values of both aggregation and solvation in a number of organolithium systems was studied in this paper, i.e. different arylamides, phenolates, enolates, substituted phenyllithium complexes and lithium phenylacetylide. 

An unexpected result was obtained when DTBB-catalyzed lithiation was applied to the vinyl-oxetane 313 . After work-up, lactone 314 was isolated, the process being explained by an elimination reaction via a radical pathway more than by reduction of the benzyl radical into the anion. Thus, this hypothetical intennediate reacted with the lithium enolate of acetaldehyde, generated in situ by reductive decomposition of THF (Scheme 92). 

SCHEME 86. Trajectory of the approach403 and transition state models for the reaction of monomeric and dimeric lithium enolate of acetaldehyde with MeCl405... 

SCHEME 107. Relative energies and geometries for the O- and C-addition transition state calculated for the addition of formaldehyde to the lithium enolate of acetaldehyde and the preferred conformations of aldol535... 

Abbotto, Streitwieser and Schleyer performed an exhaustive study, using the B3LYP /6-31-bG //PM3 calculation level, on the effect of dimethyl ether solvation on aggregated forms of the lithium enolate of acetaldehyde (CH2=CH0Li) (Me20) c. 

Pratt and Streitwieser performed ab initio (HF/6-31G and HF/6-311-FG ) calculations to examine the formation of mixed dimer and trimer aggregates between the lithium enolate of acetaldehyde (lithium vinyloxide, LiOVi) and lithium chloride, lithium bromide and lithium amides. Gas-phase calculations showed that in the absence of solvation effects, the mixed trimer (LiOVi)2 LiX (20) was the most favored species. 

TABLE 12. Comparison of AE and AG calculated at two levels of theory, for intermediates derived from the lithium enolates of acetaldehyde in three reactions carried out at 298.15 K... 

The only sensible place to lithiate the starting material (which is, of course, the popular solver. THE) is next to the oxygen atom. A reverse cycloaddition then eliminates ethylene (ethene) arc gives the lithium enolate of acetaldehyde. It is easier to see the reverse cycloaddition if we write the lithium derivative as an anion. 

H This chemistry was used to make The intermediate A is the lithium enolate of acetaldehyde formed in the absence of an -a new protecting group (A. J. Duggan acetaldehyde (see p. 707 for the importance of this). It acylates on oxygen with the acid chloride i ... 

Therefore, our first idea was to 0-acylate simple enolates with phosgene. In a first course of attempts, we investigated the reaction of phosgene with alkaline metals enolates. For example we prepared lithium enolate of acetaldehyde through cleavage of tetrahydrofuran by n- butylllthium (Ref. 116) and reacted with phosgene under various conditions. Unfortunately, no trace of vinyl chloroformate was found in all experiments performed [Scheme 90]. 

Figure 2 Geometries for the oxygen transfer of an oxaziridine to the lithium enolate of acetaldehyde.

Lithium alkyls, e.g. -butyllithium, also effect ring-opening. First, 2-lithiotetrahydrofuran is formed, which at room temperature slowly decomposes through a [3+2] cycloreversion into ethene and the lithium enolate of acetaldehyde ... 

Reaction of n-butyl-lithium with tetrahydrofuran at 25 C for 16 h affords the lithium enolate of acetaldehyde. This enolate O-acylates and O-silylates readily C-alkylation is accomplished by initial formation of the tributyltin enolate followed... 

DFT and Car-Parrinello molecular dynamics simulations have been used to study aggregation effects in model aldols, using the lithium enolates of acetaldehyde and acetone, with formaldehyde and acetone as electrophiles. The core of the aggregates is Li 0 ... 

Tetrahydrofuran is cleaved by n-butyl-lithium to yield ethylene and the lithium enolate of acetaldehyde a symmetry-allowed +, 2,] cycloreversion of the anion (570) is considered the most likely mechanism. ... 

Lithiations. f-Butyllithium is less frequently used for proton abstraction than is butyllithium or sec-butyllithium. However, as it is more reactive and less nucleophilic than its isomers, t-BuLi may be the reagent of choice for the lithiation of relatively weak acids (eq 1). The addition of 1 equiv of a tertiary polyamine increases the metalating ability of the reagent. Simple hydrocarbons, which are used as solvents, are generally inert to lithiation by f-BuLi. Although ethers and amines are often used as solvents in low temperature reactions involving r-BuLi, ethers, THF, and TMEDA are readily lithiated by the reagent. Indeed, treatment of THE with f-BuLi has been reported to afford ethylene and the lithium enolate of acetaldehyde at temperatures as low as -78 °C. ... 

The Cobalt Triad.— The first methylene-bridged binuclear cobalt complex [Ck)2O-CO)0i-CH2)(C5Mes)2] has been obtained by treatment of C0CI2 with lithium pentamethylcyclopentadienide and the lithium enolate of acetaldehyde (Li+CHaCHO-). The novel transannular electron-rich olefin (35) reacts with f RhCl(cod) 2] to form the chelating c -dicarbenerhodium(i) salt (36) [X=RhCla-... 

The decomposition of THF with n-butyllithium is a very efficient method for producing the lithium enolate of acetaldehyde. The reaction is easily rationalized by assuming deprotonation in the a-oxygen position, followed by a [2-1-3] cycloreversion of the anion 186. The enolate 187 resulting under concomitant liberation of ethylene has been trapped by different electrophiles among them the silylation proves the existence of the enolate [176]. 

Support for this identification of the monomer as the most reactive under the different species of lithium enolates came from Streitwieser s computational study on a model that involves the alkylation of the lithium enolate of acetaldehyde. 

Figure 3.7 Computed transition structures (HF 6-31-ng ) for the reaction monomeric (top) and dimeric (bottom) lithium enolate of acetaldehyde with methyl chloride. Copied from Ref. [29],...

Figure 3.10 (a) Calculated global minimum of unsolvated lithium enolate of acetaldehyde and (b) calculated O-bound global minimum of lithium enolate of acetone, tri-solvated by dimethyl ether. Copied from Ref. [39a]. 

Thus, lanthanide (Lu and Yb) and yttrium enolates, which were prepared from the lithium enolate of acetaldehyde and the corresponding dimeric dicyclopenta-dienyl metal chlorides [Cp2MCl2]2> were studied by NMR and IR spectroscopy, and clear evidence for the O-bound tautomer was provided in all cases. This was confirmed by a crystal structure of dimeric yttrium enolate 17 with a Y2O2 core unit > [51]. The chelate complex 18 of scandium, on the other hand, has been shown by a crystal structure to be monomeric. Here again, the metal is bound to the enolate oxygen atom (Scheme 3.7) [52]. 

Titanium bis-enolate 19, readily available by transmetallation of the lithium enolate of acetaldehyde with dicyclopentadienyl titanium dichloride (Cp2TiCl2), was characterized by a crystal structure analysis [53, 54]. Mono-enolates of titanium and zirconium 20 were obtained analogously from Cp2Ti(Me)Cl and... 

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