A Lewis acid is needed in order to allow the [2, 3]-sigmatropic rearrangement of N-alkyl N- allyl α-amino esters to give rise to N-alkyl C-allyl glycine esters. Addition of iodomethane, rather than a Lewis acid, promotes quaternary ammonium salt formation, in situ ylide formation and [2, 3]-sigmatropic rearrangement to N, N-dialkyl C-allyl glycine esters.