jo990412u_si_001.pdf (1.27 MB)
New Homochiral Ligands Bearing Nonstereogenic Chirotopic Centers. Lithiated N,N‘-Dialkylureas as Chiral Bases and Sterically Crowded Phosphines for Asymmetric Catalysis
journal contribution
posted on 1999-06-24, 00:00 authored by Claus-Dieter Graf, Christophe Malan, Klaus Harms, Paul KnochelThe 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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ureas 2eeC 2monophosphine 3Chiral BasesLithiated NligandketoneNew Homochiral Ligands Bearing Nonstereogenic Chirotopic Centersnonstereogenic chirotopic centerachiral stericallyenantiomerictype 1alkylationsynthesisalkyl diphosphine 23allylationSterically Crowded Phosphinesdimethyl malonateDialkylureaAsymmetric Catalysishomochiralenantioselective deprotonationPd
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