Self‐Assembly of Heterobimetallic Complexes and Reactive Nucleophiles: A General Strategy for the Activation of Asymmetric Reactions Promoted by Heterobimetallic Catalysts

Abstract

Abstract Heterobimetallic asymmetric catalysts, such as the lanthanum–lithium–binaphthol complex (La Li–BINOL), the aluminum–lithium–binaphthol complex (AlLi–BINOL), and a newly prepared gallium–sodium–binaphthol complex (Ga Na–BINOL), have been self‐assembled with reactive nucleophiles, such as lithium nitronates and sodium malonates, to generate more efficient catalysts than the parent heterobimetallic catalysts. For example, by the combined use of La Li–BINOL (1 mol%; contains one H 2 O molecule) and BuLi (0.9 mol%) as the catalyst system, asymmetric nitroaldol reactions are greatly accelerated in all cases without a decrease in the optical purity of the nitroaldol products. Kinetic analyses have also been carried out on the Ga Na–BINOL‐catalyzed Michael reaction of dibenzyl malonate with cyclohexenone, with or without NaO t Bu. The calculated rate constants show that the combined use of Ga Na–BINOL and NaO t Bu as the catalyst gives reaction rates that are about 50 times faster than with Ga Na–BINOL alone. This activation method should be useful for other asymmetric reactions catalyzed by heterobimetallic complexes.