Organocatalysis in Conjugate Amine Additions. Synthesis of β-Amino Acid Derivatives

Conjugate addition of O-protected hydroxylamines to pyrazole-derived enoates proceeds with high efficiency and enantioselectivity when chiral thioureas are used as activators. A wide variety of substrates undergo conjugate amine addition providing access to enantioenriched β-amino acid derivatives. Structural requirements for the optimal thiourea catalyst have been established, and the results suggest that it operates as a bifunctional catalyst.