Corey’s internal quench

Enantioselective deprotonation of prochiral 4-alkylcyclohexanones using certain lithium amide bases derived from chiral amines such as (1) has been shown (73) to generate chiral lithium enolates, which can be trapped and used further as the corresponding trimethylsilyl enol ethers trapping was achieved using Corey s internal quench described above. 

Conjugate addition, 34-5, 51-2,53, 132, 133 Conjugate hydroxymethylation, 59-60 Copper(n) bromide, 54 Copper([) chloride, 120 Copper(n) chloride, 120 Copper(i) cyanide, 7,52, 53 Copper(i) iodide, 54 Corey s internal quench, 104 Cyanohydrin trimethylsilyl ether, 137 Cycloaddition. 34,112 Cydobutane-l,2-dione, 135 Cyclohept-2-dione, 135 Cyclohex-2-enone, 52,123 Cyclohcxa-1,3-diene, 26 Cyclohexane carboxaldehyde, 22-3,69 73,78... 

The most predictable results are obtained with conformation-ally rigid systems, such as those represented in eqs 5 and 6, which possess axially oriented a-protons. This minimizes complications resulting from the presence of diastereotopic a-protons, although unexpected modes of deprotonation have been described with related chiral amides, which may involve boat conformations. To prevent enolate equilibration (with the resulting loss of stereoselectivity), Corey s internal quench method for enolate trapping with silyl chlorides is frequently used. The stereospecificity of this deprotonation is highly dependent on solvent and temperature conditions. Best results are obtained at —100 °C or lower temperatures, with THF as the solvent. 

Using Corey and Gross s internal quench method48 with TMSC1, silylenol ethers have been generated upon deprotonation of 4-substituted cyclohexanone with chiral lithium amides as shown in Scheme 20. It has been noted that the internal quench condition is crucial for achieving high level of enantioselectivity. 

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See also in sourсe #XX -- [ ]

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