Enantioconvergent Cu-Catalyzed Intramolecular C–C Coupling at Boron-Bound C(sp 3 ) Atoms of α-Aminoalkylboronates Using a C 1 -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 ( R )-configured 3-arylisoindolinones with high enantiopurity using right-handed helical PQXbpy as a chiral ligand in a toluene/CHCl 3 mixed solvent. When enantiopure ( R )- and ( S )-configured boronates were separately reacted under the same reaction conditions, both afforded ( R )-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 ( S )-products from the racemic starting material.