Crystal structures of chiral 2-[bis-(2-chloro-eth-yl)amino]-1,3,2-oxaza-phospho-lidin-2-one derivatives for the absolute configuration at phospho-rus.

'Nitro-gen mustard' bis-(2-chloro-eth-yl)amine derivatives (2 R ,4 S ,5 R )- and (2 S ,4 S ,5 R )-2-[bis-(2-chloro-eth-yl)amino]-3,4-dimethyl-5-phenyl-1,3,2-oxaza-phos-pho-lidin-2-one ( 2a and 2b , respectively), C14 H21 Cl2 N2 O2 P, and (2 R ,4 R )- and (2 S ,4 R )-2-[bis-(2-chloro-eth-yl)amino]-4-isobutyl-1,3,2-oxaza-phospho-lidin-2-one ( 3a and 3b , respectively), C10 H21 Cl2 N2 O2 P, were synthesized as a mixture of diastereomers through a 1:1 reaction of enanti-omerically pure chiral amino alcohols with bis-(2-chloro-eth-yl)phospho-ramidic dichloride. Flash column chromatography yielded diastereomerically pure products, as supported by 31 P NMR. The crystal structures of 2b and 3b were obtained to determine their absolute configuration at phospho-rus, and 31 P NMR chemical shift trends are proposed based on the spatial relationship of the bis-(2-chloro-eth-yl)amine moiety and the chiral substituent of the amino alcohol. Oxaza-phospho-lidinones were observed to have a more downfield 31 P NMR chemical shift when the aforementioned substituents are in a syn configuration and vice versa for when they are anti .