DBU-Mediated Diastereoselective (3+2)-Cycloaddition of Isatin Ketonitrones and Coumarins to Construct Coumarin-Fused
Lan Ma1, Qian Zhong1, Zixin Zhang1
1College of Science, Sichuan Agricultural University, Ya'an 625014, China.
Abstract:
The synthesis of novel dicyclic spiropyrrolidine oxoindole derivatives is described. This approach relies on a (3+2)-cycloaddition reaction between coumarins and isatin ketonitrone 1,3-dipoles, which were formed in situ by condensation of various substituted isatins with arylhydroxylamines. The corresponding pentacyclic products, featuring four contiguous stereocenters-including two quaternary carbon stereocenters fused within a single ring system-were obtained smoothly in moderate to excellent yields (22-98%), with high regioselectivity (α and exo type) and diastereoselectivity (>20:1 dr). Over 45 examples of the synthesized compounds were fully characterized using a range of spectroscopic techniques, including single-crystal X-ray diffraction, FTIR, NMR, and mass spectrometry.
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