Studies on the Syntheses of N-Heterocyclic Compounds. V. 2-Aryl-5, 8-dichloropyrimido [4, 5-d] pyridazine

Abstract

2-Substituted-5, 6, 7, 8-tetrahydropyrimido [4, 5-d] pyridazine-5, 8-diones (6) having a variety of substituents at 2-position were synthesized. Chlorination reaction of 6 were carried out, and it was found that only the compound which have aryl substituent at 2-position could be converted to 2-aryl-5, 8-dichloropyrimido [4, 5-d] pyridazine (14), while other derivatives gave no corresponding dichlorides (14). 2, 4-Diphenyl-5, 6, 7, 8-tetra-hydropyrimido [4, 5-d] pyridazine-5, 8-dione (9) was not obtained because of its structural unstability caused by steric interference of phenyl group at 4-position.