New Homochiral Ligands Bearing Nonstereogenic Chirotopic Centers. Lithiated N,N‘-Dialkylureas as Chiral Bases and Sterically Crowded Phosphines for Asymmetric Catalysis
摘要:
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.
New Homochiral Ligands Bearing Nonstereogenic Chirotopic Centers. Lithiated <i>N</i>,<i>N</i><i>‘</i>-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.
Asymmetric hydroboration with new chiral monoalkylboranes bearing a non-stereogenic, chirotopic center
作者:Claus-Dieter Graf、Paul Knochel
DOI:10.1016/s0040-4020(99)00445-7
日期:1999.7
c acids bearing a non-stereogenic, chirotopic center were prepared via stereoselective coppercatalyzed carbon-carbon bond forming reactions. These compounds serve as intermediates in the synthesis of new chiral monoalkylboranes which lead to enantio-selectivities of up to 64% ee in the asymmetrichydroboration of cyclic olefins.