lsulfanyl-3,4-dihydro-pyrido[4,3-d]pyrimidine-8-carbonitriles , were synthesized via a facile annulation process in which formation of the pyrimidine ring proceeded smoothly by the regioselective attack of a formamidate group on a neighboring carbonyl group instead of a cyano group. Bioassay results indicated that these compounds showed significant herbicidal activity at a dose of 100 μg/mL on the