Asymmetric Synthesis of Optically Active Pyrazolidines or Pyrazoline Derivatives via Ni(II)-Bipyridine-N,N′-dioxide Complexes

Easily obtainable and efficient chiral C₂-symmetric bipyridine-N,N'-dioxide ligands with Ni(OTf)₂ were developed for application in catalyzing [3 + 2] cycloaddition reactions to synthesize optically active fused pyrazolidines or pyrazoline derivatives featuring three contiguous stereogenic centers by employing azomethine imines and α,β-unsaturated 2-acyl imidazoles, affording the corresponding adducts with the opposite configuration compared to previous synthetic products in 80-98% yields with 28-99% ee and >20:1 dr. In addition, subsequent amplification experiments and derivative transformations of the product further demonstrated the efficient catalytic performance of the catalyst Ni(II)-bipyridine-N,N'-dioxide complexes and the practicality of this synthesis methodology.