Synthesis of enantiomerically pure P-stereogenic diphosphacrowns and their palladium complexes.

A practical synthetic route for enantiomerically pure P-stereogenic diphosphacrowns was developed by using a P-stereogenic bisphosphine as a chiral building block. Their molecular structures were confirmed by NMR spectroscopy and X-ray crystallography. Complexation of the diphosphacrowns with palladium was carried out, and the corresponding palladium complexes were obtained. The P-stereogenic diphosphacrowns were applicable to the chiral ligand for the asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated ketone catalyzed by palladium. This reaction proceeded smoothly to afford the corresponding 1,4-addition products in high yield with good enantioselectivities.