Enantioselective Nucleophilic β‐Carbon‐Atom Amination of Enals: Carbene‐Catalyzed Formal [3+2] Reactions

An enantioselective β‐carbon amination for enals is disclosed. The nitrogen atom from a protected hydrazine with suitable electronic properties readily behaves as a nucleophile. Addition of the nitrogen nucleophile to a catalytically generated N‐heterocyclic‐carbene‐bound α,β‐unsaturated acyl azolium intermediate constructs a new carbon–nitrogen bond asymmetrically. The pyrazolidinone products from our catalytic reactions are common scaffolds in bioactive molecules, and can be easily transformed into useful compounds such as β 3 ‐amino‐acid derivatives.