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%.