Developments in Organocatalysis Transformations of Unsaturated Pyrazolones.

Unsaturated pyrazolones can participate in organocatalytic reactions with various substrates to form spiro-cyclic pyrazolones, and fuzed-pyrazolone heterocycles. The present review describes progress since 2013 in the organocatalysis transformations of unsaturated pyrazolones. Pyrazolones are prevalent structural motifs in a wide variety of natural products and drug or drug-like molecules. A series of nitrogen-containing pyrazolones exhibits anticancer, antimicrobial, anti-inflammatory, anticonvulsant, antidepressant, antidiabetic, and antipyretic activities. Especially, chiral spiro-cyclic pyrazolones are recognized as targets in natural products and clinical pharmaceuticals. Organocatalytic systems are powerful and reliable approaches that allow us to build structurally complex molecules in an enantioselectively and diastereoselectively manner. Avoiding the use of transition metal catalysts, readily available bifunctional organocatalysts, and the performance of the reaction at ambient temperature are other advantages of these catalytic systems. Despite considerable progress in this field, it is still one of the challenging goals for chemists to make new biologically active heterocyclic molecules.