Rhodium/Chiral Diene Complexes in the Catalytic Asymmetric Arylation of β‑Pyrazol-1-yl Acrylates

The asymmetric conjugate addition of arylboronic acids to substituted and unsubstituted β-pyrazol-1-yl (E)-tert-butyl acrylates 4 catalyzed by 5 mol % of the Rh­(I)/diene 2a catalyst provided the corresponding addition products in 44–98% yield and 91–>99.5% ee. The method was applied to the formal synthesis of (3S)-3-aryl-3-(pyrazol-1-yl)­propanoic acid 1b with agonistic activity toward the human GPR40 G-protein coupled receptor.