Issue 10, 2023

Catalytic asymmetric [4 + 1] cycloaddition to synthesize chiral pyrazoline-spirooxindoles

Abstract

An asymmetric formal [4 + 1] cycloaddition of N-unprotected oxindole 3-pyridinium salts and α-halo hydrazones to access chiral pyrazoline-spirooxindoles is realized by using a chiral N,N′-dioxide-Pr(OTf)3 complex as a catalyst. The process includes base-promoted in situ formation of oxindole 3-pyridinium ylides and azoalkenes, followed by an asymmetric [4 + 1] annulation. The efficient enantiocontrol benefits from low temperature, which weakens the strong background reaction, and hydrogen bonding between the oxindole scaffold in the substrate and H2O in the catalyst, which prevents the plane flip of the oxindole ring. A range of bioactive chiral pyrazoline-spirooxindole derivatives are obtained in good yields with excellent ee values.

Graphical abstract: Catalytic asymmetric [4 + 1] cycloaddition to synthesize chiral pyrazoline-spirooxindoles

Supplementary files

Article information

Article type
Research Article
Submitted
02 3 2023
Accepted
09 4 2023
First published
14 4 2023

Org. Chem. Front., 2023,10, 2422-2428

Catalytic asymmetric [4 + 1] cycloaddition to synthesize chiral pyrazoline-spirooxindoles

K. Hu, D. Zhang, S. Wang, L. Lin and X. Feng, Org. Chem. Front., 2023, 10, 2422 DOI: 10.1039/D3QO00320E

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