Prepn: Boese, US 2138756 (1938 to Carbide and Carbon Chem.); Gleason, US 2174239 (1939 to Standard Oil). Synthesis from urea and ethyl acetoacetate: J. J. Donleavy, M. A. Kise, Org. Synth. coll. vol. II, 422 (1943); by isomerization of 2-hydroxy-4-methoxy-6-methylpyrimidine: McOmie et al., J. Chem. Soc. 1957, 1830; from urea and diketene: Khromov-Borisov, Karlinskaya, J. Gen. Chem. USSR 26, 1728 (1956); SU 101690 (1955), C.A. 51, 12989f (1957).