Synthesis of Type II β-Turn Surrogate Dipeptides Based on <i>s</i><i>yn</i>-α-Amino-α,β-dialkyl-β-lactams

The achiral bis(trimethylsilyl)methyl group acts as an efficient stereochemical determinant of the α-alkylation reaction in β-branched α-phenyloxazolidinyl- or α-diphenyloxazolidinyl-β-lactams and provides the first stereocontrolled access to syn-α-amino-α,β-dialkyl(aryl)-β-lactams. These products are readily transformed into type II β-turn mimetic surrogates 2B.