A C2-Symmetric Chiral Bis-Sulfoxide Ligand in a Rhodium-Catalyzed Reaction: Asymmetric 1,4-Addition of Sodium Tetraarylborates to Chromenones

A new C-2-symmetric chiral bis-sulfoxide ligand, (R,R)-1,2-bis(tert-butylsulfinyl)benzene, has been designed and prepared by the reaction of (R)-benzyl tert-butylsulfoxide with (R)-thiosulfinate. This ligand exhibits excellent enantioselectivities in the Rh-catalyzed asymmetric 1,4-addition reaction. In particular, the present work has realized access to optically pure flavanones for the first time through 1,4-addition of arylboronic reagents to chromenones.