Iridium-Catalyzed Diastereo-, Enantio-, and Regioselective Allylic Alkylation with Prochiral Enolates

Transition-metal-catalyzed asymmetric allylic alkylation of enolates is a powerful method for the formation of carbon− carbon bonds. Within this field, palladium-catalyzed allylic alkylation reactions have undoubtedly been the most studied. Aside from limited cases, palladium catalysts preferentially form the linear substitution product through alkylation at the less-substituted terminus of the allylic electrophile (Scheme 1). However, in contrast to palladium, most other transition metals (e.g., Mo, W, Fe, Ru, Co, Rh, Ni, Pt, and Ir) have been shown to favor the construction of the branched product, with iridium catalysts being some of the most efficient and selective. The potential application of these chiral, branched products to the synthesis of natural products and biologically active compounds has motivated the development of practical and reliable transition-metal-catalyzed methods for their construction.