Catalytic Asymmetric Synthesis and Reactions of Enolates

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Enolates play a central role insynthetic organic chemistry. Studies have been carried out on the possibility of making the synthesis and reactions of lithium enolates enantioselective through the agency of chiral chelated lithium amides or their corresponding amines. Based on the analysis of these reactions, attempts have also been made to convert them catalytic as to the chiral bases used.1. Catalytic Asymmetric Deprotonation :The rate of deprotonation of carbonyl compounds by a tridentate lithium amide is reasonably slower than that by a bidentate lithium amide. Based on this new finding, catalytic asymmetric deprotonation of carbonyl compounds was realized for the first time by using a combination of a chiral bidentate amine and an achiral tridentate lithium amide.2. Catalytic Asymmetric Alkylation :The rate of alkylation of lithium enolate in the presence of a tetradentate amine is reasonably faster that that in the presence of a bidentate amine. Basedon this new finding, catalytic asymmetric alkylation of lithium enolates was realized for the first time by using a combination of a chiral tetradentate amine and an achiral bidentate amine.3. Catalytic Asymmetric Protonation :Catalytic asymmetric protonation of prochiral lithium enolates was realized in the presence of less than a stoichiometric amount of a chiral tetradentate amine in toluene by insoluble achiral proton sources such as succinimide. Mechanistic details are still under investigation.