Asymmetric [3 + 3] Annulation of Copper–Allenylidenes with Pyrazolones: Synthesis of Chiral 1,4-Dihydropyrano[2,3‑<i>c</i>]pyrazoles
2018-08-24T16:51:08Z (GMT) by
The copper-catalyzed asymmetric [3 + 3] annulation of ethynyl benzoxazinanones with pyrazolones has been achieved, providing simple access to 1,4-dihydropyrano[2,3-<i>c</i>]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.
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