Optimised conditions for the acylation of (S)-4-(1-methylethyl)-oxazolidin-2-one 4,(R)-4- phenyloxazolidin-2-one 5 and 4-(R),(5 S)-1, 5-dimethyl-4-phenylimidazolidin-2-one 3 with 2- bromoacyl halides were developed. For imidazolidin-2-one 3 the optimum conditions require the use of the hindered bases 2, 6-di-t-butylpyridine or 2, 6-lutidine in order to reduce the ketene formation which has a strong preference for O-acylation.
