Synthesis and reactions of α-ketoaldehyde adducts of some heterocyclic ureas

Pyruvaldehyde reacts with heterocyclic ureas 4a-d giving dihydroxyimidazolidin-2-ones 5a-d . Phenyl glyoxal reacts with 4a giving an analogous adduct 5e . These 1,2-diols are smoothly dehydrated to hydantoins 9a-e which on mild reduction provide monohydroxyimidazolidin-2-ones 10a-e . Cis and trans isomers of 10d have been isolated and observed to epimerise under suitable conditions. An unusual halogenation converts 5a to the bromomethyl derivative 14b which is a convenient starting material for the synthesis of 4-substituted imidazolin-2-ones such as 15, 16, 17, 18 and 19 .