Abstract 1-Phenyl-3-(1, 2-dimethyl-3-oxo-1-butenyl) urea (III) has been prepared by reaction of phenyl isocyanate with 4-amino-3-methyl-3-penten-2-one (I). Ethyl 2-methyl-3-N-(N'- phenylureido)-2-butenoate (V) has been prepared by analogous reaction with ethyl 3-amino- 2-methyl-2-butenoate (II). Kinetics have been measured of acid and base catalyzed cyclization of III and that of base catalyzed cyclization of V giving 1-phenyl-4, 5, 6- ...