Isolated from the basic fraction of coal tar: Heap et al., J. Am. Chem. Soc. 43, 1936 (1921); from a bone oil fraction: Ladenburg, Roth, Ber. 18, 51 (1885). Synthesis from ethyl acetoacetate, formaldehyde, and ammonia: Singer, McElvain, Org. Synth. coll. vol. II, 214 (1943).