New stereoselective alkylation methodology is presented for formation of chiral, non-racemic quaternary centres via a chiral auxiliary protocol involving alpha-alkylated malonate imidazolidinones. Based on two X-Ray structures of quaternized products, the diastereoselectivity observed may be rationalised via a transition-state involving an s-transC-N conformation of the C-N bond of the auxiliary, with the metal cation (K+) chelated into the malonate six-membered hole as a Z-enolate. A deprotection protocol involving ethanethiolate exchange of the imide to the corresponding thioester, followed by a standard Fukuyama reduction and a borohydride reduction furnishes alpha, alpha'-quaternized beta-hydroxypropionates in high ee overall.