Cinchona alkaloid catalyzed enantioselective amination of α,β-unsaturated ketones: an asymmetric approach to Δ(2)-pyrazolines

Δ(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 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 considerable range of optically active 3,5-dialkyl 2-pyrazolines.