Asymmetric [3 + 3] Annulation of Copper–Allenylidenes with Pyrazolones: Synthesis of Chiral 1,4-Dihydro­pyrano­[2,3‑c]­pyrazoles

The copper-catalyzed asymmetric [3 + 3] annulation of ethynyl benzoxazinanones with pyrazolones has been achieved, providing simple access to 1,4-dihydropyrano­[2,3-c]­pyrazole derivatives in moderate to excellent yields with excellent enantioselectivities (up to 99% ee). Compared with previous annulation reactions of copper–allenylidenes from ethynyl benzoxazinanones, the current reaction fused the three carbon atoms of the propargyl moiety into a heterocyclic framework.