Pyridazinones from maleic hydrazide: a new substrate for the Mitsunobu reaction

Abstract

Crystal engineered organic frameworks assembled using hydrogen bonding are known, and examples constructed from hydroxypyridine/pyridone as the dominant source of hydrogen bonding have been reported. Less explored are analogous systems based on maleic hydrazide. Herein, a two-step route (Mitsunobu followed by Schiff base reactions) to asymmetrically substituted pyridazinones from maleic hydrazide (step 1) is reported with 2-, 3-, or 4-pyridinecarboxaldehyde (step 2). Upon reaction with 4-pyridinecarboxaldehyde, single crystals suitable for analysis via X-ray diffraction were obtained. Careful examination of this solid state structure and comparison with a large number of related structures in the Cambridge Structural Database revealed a pyridazinone (vs. pyridazinol) core and persistent [Formula: see text] “head-to-tail” hydrogen bonded dimers. Although these pyridazinones were originally considered suitable for use as ligands for metal cation coordination, challenges in achieving this outcome were encountered.