Organocatalytic Amination of Pyrazolones with Azodicarboxylates: Scope and Limitations

The organocatalytic amination of pyrazol‐5‐ones with azodicarboxylates (catalyzed by quinine) is reported. This asymmetric process furnishes enantiomerically enriched hydrazine adducts containing quaternary stereocenters in high yields (74–96 %) and enantioselectivities (up to ee 97 %). Theoretical calculations allow us to propose the relations between quinine catalyst and reactants leading to observed stereochemical outcome and trends in the effectivity of the reaction. An asymmetric method for the amination of pyrazol‐5‐ones using azo compounds is described. The developed process exhibits a wide substrate scope and high efficiency in terms of yield and enantioselectivity.