Asymmetric Michael/Aromatization Reaction of Azlactones to α,β-Unsaturated Pyrazolones with C-4 Regioselectivity Catalyzed by an Isosteviol-Derived Thiourea Organocatalyst

Pyrazoles are an important class of molecular structures with significant biological and pharmaceutical activities. Herein, heterocyclic compounds containing both a pyrazole motif and a masked amino acid structure are synthesized through the asymmetric Michael/aromatization of azlactones to alpha,beta-unsaturated pyrazolones by using isosteviol-derived amine thiourea as the organocatalyst. The products are obtained in good yields (up to 93%) with good diastereoselectivities and good enantioselectivities (up to >10:1 dr, 97% ee).