Organocatalytic [3 + 3] Annulation of Pyrazolinone and Chromone–Indandione Derivatives: Access to Spiropyrazolone-Fused Tetrahydroxanthones

Spiropyrazolone and tetrahydroxanthone are privileged heterocyclic architectures that are known for their diverse biological activities. Herein, we report a bifunctional squaramide-catalyzed [3 + 3] annulation approach for the asymmetric synthesis of spiropyrazolone-fused tetrahydroxanthone scaffolds from pyrazolinone and a chromone–indandione-derived 3C synthon. This integrated cascade reaction provided optically active scaffolds in moderate to excellent yields and enantioselectivities with excellent diastereoselectivity. Control experiments revealed mechanistic insights, and synthetic applications further highlighted the significance of this methodology.