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Highly Chemoselective and Enantioselective Synthesis of 3,4‑2H‑Pyrindin-2-ones by an NHC-Catalyzed [3 + 3] Cyclization
journal contribution
posted on 2020-03-10, 21:29 authored by Jun Yan, Zhaoxin Song, Chengtao Zhao, Kuangxi Shi, Limin Yang, Guofu ZhongA highly
chemoselective and enantioselective cyclization of γ-chloroenals
and ketimines has been developed to synthesize enantiopure 3,4-2H-pyrindin-2-ones as major products. It is proposed that
the intermediate enone IV reacted with an enamine to
proceed with a [3 + 3] cyclization, thereby affording 3,4-2H-pyrindin-2-ones as major products. Interestingly, the
addition of LiCl promoted the formation of the enamine and accelerated
the [3 + 3] cyclization. In contrast, the [4 + 2] cycloaddition reaction
between the intermediate vinyl enolate VIII and an imine
offered 5,6-2H-pyrindin-2-ones as minor products.
This protocol represents the exceptional potential of N-heterocyclic
carbene (NHC) catalytic reactions in accessing biologically active
3,4-2H-pyrindin-2-one derivatives in good yield with
high chemoselectivities and excellent enantiomeric purities.