Enantioselective Synthesis of 1 H ‐Pyrazolo[1,2‐ b ]pyridazine‐5,10‐dione Derivatives via an Organocatalytic Three‐Component Cascade Reaction

Efficient stereoselective synthesis of 1 H ‐pyrazolo[1,2‐ b ]phthalazine‐5,10‐diones through one‐pot condensation of an aldehyde, malononitrile (cyanoacetate) and phthalhydrazide is described for the first time. 1‐[3,5‐Bis(trifluoromethyl)phenyl]‐3‐[( 1R,2R )‐2‐(pyrrolidin‐1‐yl)cyclohexyl]thiourea (Takemoto's catalyst) was identified as an optimal organocatalyst to promote the tandem Knoevenagel/Michael/cyclization reaction to yield the desired products in good yields (52%–92%) with up to 99% enantiomer excess (ee).