The reaction 5-amino-2-phenyl-3,4-dihydro-3H-pyrazol-3-one with activated lactams (lactim ethers, lactam acetals, and methylthioalkylidene iminium salts) was investigated. It occurs on the active methylene group of 5-amino-2-phenyl-3,4-dihydro-3H-pyrazol-3-one to furnish cyclic enamines, 5-amino-4-(2-azacycloalkylidene)-2-phenyl-2,4-dihydro-3H-pyrazol-3-ones and 5-amino-4-(1-methyl-2-azacycloalkylidene)-2-phenyl-2,4-dihydro-3H-pyrazol-3-ones.