title: New Homochiral Ligands Bearing Nonstereogenic Chirotopic Centers. Lithiated N,N'-Dialkylureas as Chiral Bases and Sterically Crowded Phosphines for Asymmetric Catalysis.
abstract: 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.
authors.affiliation: Fachbereich Chemie der Philipps-Universität Marburg, D-35032 Marburg, Germany, and Institut für Organische Chemie, LMU-München, Butenandtstrasse 5-13, D-81377 München, Germany.
authors.forename: Claus-Dieter
authors.initials: CD
authors.lastname: Graf
authors.forename: Christophe
authors.initials: C
authors.lastname: Malan
authors.forename: Klaus
authors.initials: K
authors.lastname: Harms
authors.forename: Paul
authors.initials: P
authors.lastname: Knochel