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