| In the field of catalytic, asymmetric synthesis, there is a growing emphasis on multifunctional systems in which multiple parts of a catalyst, or multiple catalysts, work together to promote a specific reaction. These efforts, in part, are result-driven, and they are also part of a movement towards emulating the efficiency and selectivity of nature's catalysts, enzymes. In this Dissertation, the importance of bifunctional catalytic methods is illustrate, focusing on the cooperative action of Lewis acidic and Lewis basic catalysts.The Lectka group has contributed five separate bifunctional methods that combine achiral Lewis acids with chiral cinchona alkaloid nucleophiles---for example, benzoylquinine (BQ)---to catalyze highly enantioselective cycloaddition reactions between ketene enolates and various electrophiles. Each method requires a distinct Lewis acid to coordinate and activate the electrophile, which in turn increases the reaction rates and yields, without any detectable influence on the outstanding enantioselectivities inherent to these reactions. All of these systems are prime examples of cooperative Lewis acid/base catalysis modes. |
