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Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
Published on: July 17, 2020
NHC-Catalyzed Asymmetric Formal [4 + 2] Annulation To Construct Spirocyclohexane Pyrazolone Skeletons
Chengtao Zhao1, Kuangxi Shi1, Gao He1
1College of Materials, Chemistry and Chemical Engineering , Hangzhou Normal University , Hangzhou 311121 , China.
Abstract:
A chiral N-heterocyclic carbene (NHC)-catalyzed [4 + 2] annulation of γ-chloroenals and α-arylidene pyrazolinones was developed in the absence of expensive oxidants. The reaction proceeds smoothly via a vinyl enolate intermediate to afford spirocyclohexane pyrazolones in moderate to good yield (up to 86%) with high diastereoselectivities (up to 15:1 dr) and excellent enantioselectivities (up to >99% ee).
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