New Homochiral Ligands Bearing Nonstereogenic Chirotopic Centers. Lithiated N,N‘-Dialkylureas as Chiral Bases and Sterically Crowded Phosphines for Asymmetric Catalysis
1999-06-24T00:00:00Z (GMT) by
The synthesis of new homochiral pseudo-C2-symmetrical ligands of type 1 bearing a nonstereogenic chirotopic center is reported. Two such structural units are combined in the ureas 2 and 10, which proved to be useful for enantioselective deprotonation and alkylation of ketones (up to 88% ee). The monophosphine 3 induced a high enantiomeric excess in the Pd-catalyzed allylation of dimethyl malonate (up to 73% ee). Furthermore, we have shown that the achiral sterically crowded alkyl diphosphine 23 efficiently stabilized Pd(0) at high temperatures.
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