Abstract
The reaction of 2-phenyl-5, 8-dichloropyrimido [4, 5-d] pyridazine (1) with a variety of primary and secondary amines afforded the corresponding mono-substituted compounds which were mixtures of two isomers, 5-substituted compound (5) and 8-substituted compound (6). Both isomers were separated and their structures were determined. Only one isomer was obtained by the reaction of 1 with morpholine or aniline under milder condition and its structure was proved to be 8-substituted compound. The reactivity of chlorine atoms at 5-and 8-position in 1 was discussed.
