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Asymmetric [3 + 3] Annulation of Copper–Allenylidenes with Pyrazolones: Synthesis of Chiral 1,4-Dihydropyrano[2,3‑c]pyrazoles
journal contribution
posted on 2018-08-24, 16:51 authored by Feng Jiang, Xinping Feng, Rou Wang, Xing Gao, Hao Jia, Yumei Xiao, Cheng Zhang, Hongchao GuoThe 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.