Cu/Ir Relay Catalysis for Regio- and Enantioselective Alkene Borylation/Allylic Alkylation

Construction of consecutive stereogenic centers with high diastereo- and enantioselectivities is a challenging task in organic synthesis. Ir-catalyzed asymmetric allylic substitution reactions with prochiral nucleophiles have evolved as an important method toward this goal. Herein, we report a Cu/Ir relay catalysis allowing for the utilization of alkylcopper reagents, in situ generated from Cu-mediated borylative difunctionalization of styrenes with B₂pin₂, as nucleophiles compatible with π-allyl-Ir electrophiles derived from linear allyl carbonates. High yields (up to 90%), excellent regio-, diastereo-, and enantioselectivities are achieved (up to >20:1 b/l, > 20:1 dr, and >99% ee) when appropriate chiral bisphosphine and phosphoramidite ligands are employed. Selective access to all four possible stereoisomers of the target molecule is realized by switching the absolute configurations of the ligands for Cu- and Ir-catalysts. DFT calculations shed light on the stereochemical models in this relay catalysis. An array of product transformations demonstrates the synthetic potential of this reaction.