Enantioconvergent Cu-Catalyzed Intramolecular C-C Coupling at Boron-Bound C(sp) Atoms of α-Aminoalkylboronates Using a -Symmetrical 2,2'-Bipyridyl Ligand Attached to a Helically Chiral Macromolecular Scaffold.

Enantioconvergent intramolecular coupling of α-(2-bromobenzoylamino)benzylboronic esters was achieved using a copper catalyst having helically chiral macromolecular bipyridyl ligand, PQXbpy. Racemic α-(2-bromobenzoylamino)benzylboronic esters were converted into ()-configured 3-arylisoindolinones with high enantiopurity using right-handed helical PQXbpy as a chiral ligand in a toluene/CHCl mixed solvent. When enantiopure ()- and ()-configured boronates were separately reacted under the same reaction conditions, both afforded ()-configured products through formal stereoinvertive and stereoretentive processes, respectively. From these results, a mechanism involving deracemization of organocopper intermediates in the presence of PQXbpy is assumed. PQXbpy switched its helical sense to left-handed when a toluene/1,1,2-trichloroethane mixed solvent was used, resulting in the formation of the corresponding ()-products from the racemic starting material.