Phosphinamide-Directed Benzylic Lithiation. Application to the Synthesis of Peptide Building Blocks

<i>N</i>-Benzyldiphenylphosphinamides are deprotonated at the NC<sub>α</sub> position diastereospecifically upon treatment with <i>t</i>-BuLi in diethyl ether at low temperature. The reaction of the anions with alkyl, acyl, and tin halides, aliphatic and aromatic aldehydes, and Michael acceptors allowed installation of a variety of functional groups into the benzylic arm in excellent yields. Cleavage of the P−N linkage affords 1,2-amino alcohols and α-, β-, and γ-amino acids.