Conia-Ene Cyclization of Pyrazolones with <i>o</i> -Alkynyl Aldehydes: A Strategic Shift from Classical Condensation to Spiroannulation

An unprecedented, atom-economic, and regioselective Conia-Ene cyclization from readily accessible pyrazolones and <i>o</i>-alkynyl aldehydes has been developed for the synthesis of spirocyclic frameworks. This protocol operates under mild reaction conditions and offers excellent functional group tolerance while bypassing the classical condensation pathway typically favored by pyrazolones and aldehydes. Notably, the synthetic utility of this protocol is demonstrated <i>via</i> late-stage functionalization of drug molecules such as aspirin and ibuprofen, highlighting its potential in drug development and synthesis of complex molecules.