Reaction of 1-hydrazinophthalazine (1) with mesityl oxide gave five crystalline compounds, including hydrazones and their cyclization products. Isomerization of the hydrazones which were elucidated to be two geometrical isomers was discussed briefly. Structures of several products obtained by reactions of 1 with acetylacetone, tiglic aldehyde were also discussed on the basis of their spectral properties.
