Chiral Bifunctional Phosphine Ligand Enables Gold-Catalyzed Asymmetric Isomerization and Cyclization of Propargyl Sulfonamide into Chiral 3-Pyrroline

This work details an asymmetric gold-ligand cooperative catalysis that transforms readily accessible chiral/achiral propargylic sulfonamides into chiral 3-pyrrolines. A bifunctional biphenyl-2-ylphosphine ligand featuring a chiral tetrahydroisoquinoline fragment is essential for the observed metal-ligand cooperation and the asymmetric induction. 2,5-cis-3-Pyrrolines are formed with excellent diastereoselectivities in a "matched" scenario. The "mismatched" scenario by using the ligand enantiomer delivers 2,5-trans-3-pyrrolines with >5/1 diastereoselectivity. The synthetic utilities of this chemistry are demonstrated.