A novel four-step methodology for the synthesis of 5-acyl- and 5-arylsulfonyl-1,2-dihydropyrimidin-2-ones has been developed. The reaction of readily available N-[(1-acetoxy-2,2,2-trichloro)ethyl]ureas with Na-enolates of 1,3-diketones, beta-oxoesters, or alpha-arylsulfonylketones followed by heterocyclization-dehydration of the oxoalkylureas formed gave 5-acyl- or 5-arylsulfonyl-4-trichloromethyl-1,2,3,4-tetrahydropyrimidin-2-ones. The latter, in the presence of strong bases, eliminate CHCl₃ to give the target compounds. The above methodology was also used in the synthesis of 5-acyl-1,2-dihydropyrimidin-2-imines starting from N-[(1-acetoxy-2,2,2-trichloro)ethyl]-N′-guanidine.