Asymmetric Formal (3 + 2) Cyclocondensation of Coumarin-3-Formylpyrazoles as 3-Carbon Partners with 3-Hydroxyoxindoles via Esterification/Michael Addition Sequence
Shijie Zhu, Zhi-Feng Hao, Pan Ya, Ying Zhou, Xiong‐Li Liu, Ming Zhang, Chuan-Wen Lei
Abstract
The first enantioselective formal (3 + 2) cyclocondensation involving α,β-unsaturated pyrazoleamides as 3-carbon partners was accomplished in a stepwise fashion. The stepwise esterification/Michael addition sequence is promoted by Zn(OTf)2 and quinine-squaramide derivative, respectively. The protocol enables access to spiro-fused pentacyclic spirooxindoles from coumarin-3-formylpyrazoles and 3-hydroxyoxindoles in good to satisfactory overall yields (up to 91%) with excellent dr (all cases >20:1 dr) and high ee values (up to 99%). Mechanistic investigations contributed to shedding light on the enantioselective event of the process.
Topics & Concepts
CoumarinEnantioselective synthesisSquaramideMichael reactionSequence (biology)ChemistryDerivative (finance)StereochemistryCombinatorial chemistryOrganic chemistryOrganocatalysisCatalysisBusinessBiochemistryFinanceAsymmetric Synthesis and CatalysisChemical Synthesis and AnalysisSynthesis and Catalytic Reactions