Cinchona Alkaloid-Catalyzed Enantioselective Amination of α,β-Unsaturated Ketones: An Asymmetric Approach to Δ2-Pyrazolines

Delta(2)-Pyrazolines are of significant medicinal and synthetic interest due to their therapeutic properties and utility in the synthesis of 1,3-diamines, yet few asymmetric methods exist to prepare them. An unprecedented and highly enantioselective organocatalytic synthesis of 2-pyrazolines was achieved through an asymmetric conjugate addition catalyzed by 9-epi-amino Cinchona alkaloids followed by deprotection-cyclization, which furnished chiral 2-pyrazolines in 46-78% yield and 59-91% ee. This bifunctional catalytic methodology thus provides easy access to a considerable range of optically active 3,5-dialkyl 2-pyrazolines.