R‐BINOL‐Chiral Phosphoric Acid Catalyzed Regioselective Synthesis of 7‐Oxo‐Pyrazolo[1,2‐a]Pyrazoles via [3+2] Cycloaddition Reaction of Morita Baylis Hillman Adducts with N, N’‐Cyclic Azomethine Imines

Abstract

AbstractWe report an efficient [3+2] cycloaddition protocol for the synthesis of pyrazolo[1,2‐a]pyrazolones from Morita‐Baylis‐Hillman adducts and N,N’‐cyclic azomethine imines. The R‐BINOL chiral phosphoric acid was identified as the suitable catalyst for the reported cycloaddition protocol. Almost all MBH adducts regioselectively delivered 7‐oxo‐pyrazolo[1,2‐a]pyrazoles at an efficient yield of 69–91 %. With exception, the MBH adducts derived from acrylonitrile deliver 5‐oxo‐pyrazolo[1,2‐a]pyrazoles comparatively at a higher yield than the 7‐oxo‐pyrazolo[1,2‐a]pyrazoles. The density functional theory (DFT) studies demonstrate that the reaction is thermodynamically more feasible in the presence of R‐BINOL chiral phosphoric acid.