Abstract The base catalyzed hydrolysis of 2-phenyl-2-oxo-3-(2, 6-dimethylphenyl)-1, 3, 2- oxazaphospholidine, 6, and 2-phenyl-2-oxo-3-(2, 6-diisopropylphenyl)-1, 3, 2- oxazaphospholidine, 7, yields ring opened products involving 95% and 100% PO cleavage, respectively.