I. Braschi et al., HIGHLY DIASTEREOSELECTIVE ALKYLATION OF PERHYDROPYRIMIDIN-4-ONES DIRECTED TOWARD THE SYNTHESIS OF ALPHA-SUBSTITUTED BETA-AMINO ACIDS .2., Journal of organic chemistry, 59(24), 1994, pp. 7292-7298
The alkylation of several enantiomerically pure perhydropyrimidin-4-on
es at C-5 is described. For the methylation reaction, mixtures of 5,6-
trans- and cis-disubstituted adducts were obtained with high diastereo
meric ratios, whereas only the 5,6-trans-disubstituted products were o
btained with larger alkylating agents. The dialkylation reaction at C-
5 was also studied, and the 5,6-cis-trisubstituted product was prefere
ntially formed. Acidic,hydrolysis of 5,6-trans-disubstituted perhydrop
yrimidin-4-ones furnished the corresponding beta-amino acid hydrochlor
ides in quantitative yield. On cyclization of the amino acids, 5,6-tra
ns-disubstituted azetidin-2-ones were also synthesized.