New homochiral ligands bearing nonstereogenic chirotopic centers.: Lithiated N,N′-dialkylureas as chiral bases and sterically crowded phosphines for asymmetric catalysis

The synthesis of new homochiral pseudo-C-2-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.