HIGHLY DIASTEREOSELECTIVE ALKYLATION OF PERHYDROPYRIMIDIN-4-ONES DIRECTED TOWARD THE SYNTHESIS OF ALPHA-SUBSTITUTED BETA-AMINO ACIDS .2.

The alkylation of several enantiomerically pure perhydropyrimidin-4-ones at C-5 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 C-5 was also studied, and the 5,6-cis-trisubstituted product was preferentially formed. Acidic,hydrolysis of 5,6-trans-disubstituted perhydropyrimidin-4-ones furnished the corresponding beta-amino acid hydrochlorides in quantitative yield. On cyclization of the amino acids, 5,6-trans-disubstituted azetidin-2-ones were also synthesized.