Synthesis and structure of 5,7-dimethylthieno[3,4-d]pyridazine

The reaction of 2,5-dimethylthiophene-3,4-dicarboxaldehye (3) with excess hydrazine hydrate afforded the desired 5,6-fused ring thiophene derivative, 5,7-dimethylthieno[3,4-d]pyridazine (4), in high yield (82%). Pyridazine 4 was characterized spectroscopically and its structure was confirmed by X-ray crystallography. Compound 4 was observed to have an inverted, coplanar stacking arrangement in the solid state.