Iridium-Catalyzed, Highly Selective Allylation of Pyrazolones for the Convenient Construction of Adjacent Stereocenters

This paper describes an iridium-catalyzed allylation of ring-fused pyrazolones that proceeds with excellent regio-, diastereo- and enantio-selectivities. The approach exploits unactivated, racemic allylic alcohols as a source of allyl building blocks. Asymmetric syntheses of a series of biologically relevant, chiral pyrazolones highlight the utility of the methodology. The use of Cu(OTf)₂ as a co-catalyst greatly enhances the regioselectivity of the reaction and permits selective syntheses of branched allylation products.