The stereochemical outcome of the enolate dialkylation of simple phenylglycinol-derived oxazolopiperidonelactams is studied. High stereoselectivities in the generation of the quaternary stereocenter are obtainedby the appropriate choice of both the configuration of the starting lactam and the order of introductionof the substituents. The usefulness of the methodology is illustrated by the conversion of some of thedialkylated lactams into known synthetic precursors of alkaloids and by the total synthesis of(−)-quebrachamine.