Effect of the reaction medium on the bromocyclization of maleic and fumaric acid monoureides

The monopotassium salt of maleic acid monoureide is brominated in water in the same way as the free acid, whereas the trans isomer is not brominated at all. Bromocyclization of the monopotassium salt of the cis isomer to give 5-(bromocarboxy-methyl)hydantoin and intramolecular cyclization to give 5-(carboxymethyl)hydantoin are realized at pH 4–6. erythro-2,3-Dibromosuccinic acid and 5-(bromo-carboxy-methyl)hydantoin are formed in the bromination of the monopotassium salt of fumaric acid monoureide at pH 4–6. Bromination of the methyl ester of maleic acid monoureide in 1,2-dichloroethane proceeds in the same way as bromination in water to give 2-amino-5-[bromo(methoxycarbonyl)methyl]oxazolid-4-one.