The subject of this paper is the preparation of 1,3,2-oxazaphospholidi
n-4-ones by reaction of phenyldichlorophosphine with The N-methyl amid
es of alpha-hydroxy isobutyric acid and the two chiral carboxylic acid
s (S) lactic acid and (R,S) mandelic acid, which leads to diastereomer
ic products. Reaction control by means of P-31 n.m.r. demonstrates two
surprising findings: the preferred generation of the thermodynamicall
y less stable cis-isomer and an epimerization of the phosphorus chiral
ity centre at room temperature.