N-Methyl-N'-(4-fluorophenyl)urea was prepared preliminarily from 4-fluorophenyl isocyanate and methylamine by the same procedure as in Reference Example 1. The urea compound as the starting material was reacted with cyanoacetic acid to form a uracil ring. Subsequently, 6-amino-1-(4-fluorophenyl)-3-methyluracil was treated as in Reference Example 2 so that the substituent amino group at the 6-position was converted to a dimethylamino group to yield 6-dimethylamino-1-(4-fluorophenyl)-3-methyluracil. Using a mixed acid that had been prepared with sulfuric acid and nitric acid, a nitro group was introduced into the 5-position of the uracil ring and then reduced with hydrogen gas to prepare 5-amino-6-dimethylamino-1-(4-fluorophenyl)-3-methyluracil.
