Isopyrazole‐Masked Tetraketone: Tautomerism and Functionalization for Fluorescent Metal Ligands

An isopyrazole (4H-pyrazole)-embedded nonane-2,4,6,8-tetraone derivative was synthesized as a masked-tetraketone for stepwise and multiple functionalization. The has six possible tautomers, but exists predominantly 12π-electron conjugated keto-enamine-imine-enol form, which also observed in the solid state by single crystal X-ray analysis. Stepwise functionalization to introduce metal-coordination fluorescence-enhancement sites into masked tetraketone furnished fluorescent chromophore that indicates metal coordination on microgram scale considerably changing solid-state emission.