The alkylation of several enantiomerically pure perhydropyrimidin-4-ones at C5 is described. For the methylation reaction, mixtures of 5, 6-trans-and cis-disubstituted adducts were obtained with high diastereomeric ratios, whereas only the 5, 6-trans-disubstituted products were obtained with larger alkylating agents. The dialkylation reaction at C5 was also studied, and the 5, 6-cistrisubstituted product was preferentially formed. Acidic ...