Mechanistically Driven Development of Iridium Catalysts for Asymmetric Allylic Substitution
Enantioselective allylic substitution reactions comprise some of the most versatile methods for preparing enantiomerically enriched materials. These reactions form products that contain multiple functionalities by creating carbon−nitrogen, carbon−oxygen, carbon−carbon, and carbon−sulfur bonds. For many years, the development of catalysts for allylic substitution focused on palladium complexes. However, studies of complexes of other metals have revealed selectivities that often complement those of palladium systems. Most striking is the observation that reactions with unsymmetrical allylic electrophiles that typically occur with palladium catalysts at the less hindered site of an allylic electrophile occur at the more hindered site with catalysts based on other metals. In this Account, we describe the combination of an iridium precursor and a phosphoramidite ligand that catalyzes enantioselective allylic substitution reactions with a particularly broad scope of nucleophiles.
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