A novel pyrimidine derivative, N-(2-amino-4,6-dichloropyrimidine-5-yl)formamide for use, e.g., in the production of antiviral nucleotide derivatives, can be made by a process involving cyclyzing an aminomalonic ester with guanidine or its salt in the presence of a base to produce 2,5-diamino-4,6-dihydroxypyrimidine or its salt, chlorinating this product with a chlorinating agent in the presence of an amide to produce 4,6-dichloropyrimidine, and reacting the 4,6-dichloropyrimidine with an aqueous solution of a carboxylic acid to produce the N-(2-amino-4,6-dichloropyrimidine-5-yl)formamide. Novel also are 4,6-dichloropyrimidine, 4,6-dichloro-N'-(dimethylaminomethylene)pyrimidine-2,5-diamine, 4,6-dichloro-N'-(piperidine-1-ylmethylene)pyrimidine-2,5-diamine, and a process for making 2,5-diamino-4,6-dichloropyrimidine of the formula ##STR1##