Mechanistic Insights into Annulation of Arylidene‐Δ ² ‐Pyrrolin‐4‐Ones by Cinchona Squaramide‐Based Organocatalysts

Arylidene-Δ2-pyrrolin-4-ones undergo organocatalyzed annulation with malononitrile, furnishing dihydropyrano[3,2-b]pyrroles (18 examples, 0–77% ee in dichloromethane, 11–44% methanol). The products could be enantiomerically enriched by trituration (11 95–99% ee). Enantioselectivity was dependent on the nature of substrate and conformation catalyst, which turn solvent-controlled. reaction mechanism, included two pseudo-enantiomeric organocatalyst conformations, investigated experimental quantum chemical methods. mechanism consists Michael addition step followed 6-exo-dig annulation, found to rate determining step. Additionally, it identified that preferred pathway follows model originally proposed Pápai et al.