Palladium-catalyzed enantioselective dienylation of propargylic carbonates via sulfonimidamide desymmetrization.

Abstract

Asymmetric transition metal-catalyzed nucleophilic substitution of propargylic electrophiles is a powerful method for furnishing enantiomerically enriched molecules. However, catalytic enantioselective dienylation remains a significant challenge due to the lack of effective strategies for asymmetric induction and the difficulty in simultaneously controlling regio-, chemo-, and stereoselectivity. Herein, we report a palladium-catalyzed enantioselective dienylation of propargylic carbonates, enabled by a sulfonimidamide desymmetrization strategy that utilizes ion-pairing and ligand-bite-angle control. Notably, smaller-bite-angle ligands facilitate tight ion-pair formation between the cationic allenyl-Pd complex and sulfonimidamide anion, steering regioselectivity toward C2-dienylation. Leveraging this ion-pairing and ligand-directed mechanism enhances proximity and orientation effects between the prochiral sulfonimidamide anion and adjacent reactive C2-Site of the allenyl-Pd complex, enabling precise tuning of the chiral pocket around palladium center. This study demonstrates that ligand bite angle-directed counteranion positioning in cationic transition metal catalysis can serve as a general strategy for addressing challenging selectivity issues in asymmetric synthesis.