Epimerisations and non-stereospecific reactions of 1,3,2-oxazaphospholidin-2-ones and -2-thiones

Abstract

cis-2-Chloro-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidin-2-one (1a) reacts with O-ethyl thiophosphate with ca. 10% inversion and 90% retention of configuration and with fluoride ion with complete loss of stereochemistry, and (1a) and the corresponding -2-thione (2a) are epimerised to the more stable trans-isomers by pyridine and other nucleophilic catalysts; these reactions formally require an unexpected in-line exocyclic displacement at a phosphorus centre held in a five-membered ring.