An asymmetric synthesis, amenable to library preparation of structurally diverse P-chiral t-butyl substituted secondary phosphine oxides (SPOs) and tertiary phosphine oxides (TPOs), was developed. A P-chiral H-phosphinate building block was prepared via a two-step, one-pot condensation of a chiral auxiliary with t-BuPCl2, followed by hydrolysis. Nucleophilic displacement of the chiral auxiliary with Grignard reagents, followed by hydrolysis, provided a library of P-chiral SPOs. In situ treatment of the prehydrolysis intermediate with electrophiles also provided a library of P-chiral TPOs in high enantiomeric purity.