P-Chiral o-Phosphinophenol as a P/O Hybrid Ligand: Preparation and Use in Cu-Catalyzed Asymmetric Conjugate Addition of Diethylzinc to Acyclic Enones

[reaction: see text] (S)-2-(tert-Butylmethylphosphino)phenol and its methyl ether were synthesized from tert-butyldichlorophosphine via optically active phosphine-boranes as the intermediates. The former compound was used as a P/O hybrid ligand in the Cu-catalyzed asymmetric conjugate addition of diethylzinc to acyclic enones to achieve high enantioselectivity of up to 96%.