5-Chloromethylene hydantoins were prepared by condensation of ureas with chloropyruvic acid. 5-Chloromethylene thiohydantoins were prepared by chlorination of dehydroalanines followed by condensation with thiophosgene. Convenient methods for formation of aminomethylene hydantoins and thiohydantoins using N,N,N',N'-tetramethylformamidinium chloride are also reported.