PIFA-Mediated Intramolecular Dearomatization of Phenol-Tethered 1,2-Diazoles: Synthesis of Spirocyclohexadienone Pyrazolo[3,4-b]piperidinones

In recent years, the significance of spirocyclic motifs in drug discovery has increased, owing to their unique ability to engage biological targets. We present the first example of PIFA-mediated dearomative spirocyclization of phenol-tethered pyrazoles, highlighting intramolecular trapping by the pyrazole moiety. This method efficiently affords a variety of spirocyclohexadienone pyrazolo[3,4-b]piperidinones with yields of up to 82%. Mechanistic studies reveal that the dearomatization process involves a cationic intermediate.