Catalysis by excited-state palladium has emerged as an active area of research, but controlling the enantioselectivity remains a challenge. Herein, we report the use of synergistic Pd/Cu catalysis to accomplish the first three-component photochemical 1,4-bisalkylation reactions of 1,3-butadiene. Consequently, α-amino acid esters bearing quaternary stereocenters were expeditiously synthesized from three simple starting materials: an alkyl bromide, butadiene, and an aldimine ester. Experimental and computational investigation of the reaction mechanism confirmed a radical pathway involving catalysis by an excited-state palladium species. The stereochemistry is mainly controlled by the chiral Cu catalyst.
Keywords: Excited-State Palladium; Photochemical; Radical Coupling; Synergistic Catalysis; Unnatural Amino Acids.
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