Exploring Stereogenic Phosphorus: The Search for New Chiral Diphosphines

The synthesis of P-stereogenic ligands bearing 2,6-disubstituted phenyl groups at the P atom is a challenging problem. The results reported herein help define the scope and limitations of the existing synthetic protocols, such as Jugé's oxazaphospholidine borane method and the enantioselective deprotonation of P(BH3)(CH3)2(R) developed by Evans and Imamoto. Jugé's new approach based on chlorophosphine boranes was exploited for the preparation of a C1-symmetric MiniPhos-like ligand. Preliminary results concerning the application of the new ligands in the rhodium and ruthenium hydrogenation of olefins are also reported