Catalytic Asymmetric Formation and Reactions of Lithium Enolates and Elucidation of their Mechanisms

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Formation and reactions of lithium enolates constitute the most fundamental processes frequently employed in synthetic organic chemistry. We have previously reported novel enantioselective asymmetric deprotonation, alkylation, and protonation reactions. The purpose of the present research is to make these enantioselective asymmetric reactions catalytically asymmetric reactions as to the chiral amines used as chiral auxiliaries.To make these reactions catalytically asymmetric, it is necessary to find out conditions in which the reactions influenced by chiral auxiliaries proceed reasonably faster than those not influenced by chiral auxiliaries. Based on the studies on the mechanisms of these reactions, we examined various possibilities that satisfy such conditions.In enantioselective asymmetric deprotonation reactions of prochiral carbonyl compounds. we have found that the rates of deprotonation by bidentate chiral lithium amides proceed faster than those by tridentate lithium amides. We … More have also found that in situ lithium-hydrogen interchange reactions between chiral bidentate amine and achiral tridentate lithium amides occur rapidly favoring the formation of either sides, depending on the structures of these two species. Thus, using a combination of less than a stoichiometric amount of chiral bidentate amines and more than a stoichiometric amount of achiral tridentate lithium amides having appropriate structures, catalytic asymmetric deprotonation reactions as to the chiral bidentate amines were realized for the first time.In the enantioselective asymmetric alkylation reactions of prochiral lithium enolates, we have found that the rates of alkylation in the presence of bidentate amines are not enhanced, while those in the presence of tetradentate amines are reasonably enhanced. Thus, expecting fast ligand exchange reactions to the lithium between tetradentate chiral amines and bidentate achiral amines, catalytic asymmetric alkylation reactions were realized for the first time using a combination of less than a stoichiometric amount of chiral tetradentate amines and more than a stoichiometric amount of achiral bidentate amines. The same strategy was successfully applied to catalytic asymmetric protonation reactions. Less