Phosphane‐ and Amine‐Catalyzed Ring‐Opening Reactions of Cyclopropenones with Isatin Derivatives: Synthesis of Carboxylated 1H‐Indoles and Multisubstituted 2H‐Pyran‐2‐ones

Abstract The phosphane‐ and amine‐catalyzed ring‐opening reactions of cyclopropenones with isatin derivatives give different reaction outcomes. Under phosphane catalysis, carboxylated 1 H ‐indoles are afforded in good yields, and under amine catalysis, multisubstituted 2 H ‐pyran‐2‐ones are provided in moderate yields. The mechanistic aspects of these reactions are discussed on the basis of control experiments.