Helical poly­(quinoxaline-2,3-diyl)­s copolymers PQXbpy consisting of a coordinating unit, which bears a varied achiral, substituted 2,2′-bipyridyl pendant, and a chiral unit bearing chiral side chains were synthesized and used as a ligand in copper-catalyzed asymmetric cyclopropanation of olefins with diazoacetates, giving up to 91:9 er with high chemical yield. The enantioselection relied on the helical structure of PQXbpy. A single PQXbpy afforded either of a pair of enantiomers with high enantioselectivity by switching its helical sense by changing the reaction solvent from pure toluene to a 3/1 mixture of toluene and 1,1,2-trichloroethane.

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/CHCl3 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.

Enantiospecific intramolecular Suzuki-Miyauratype coupling with a-(2-halobenzoylamino)benzylboronic esters to give 3-substituted isoindolinones is achieved by using copper catalysts with 2,2'-bipyridine-based achiral ligands. Enantioenriched a-aminobenzylboron reactants bearing a hydrogen atom at the boron-bound stereogenic carbons undergo stereoinvertive coupling in the presence of a 6-phenyl-2,2'-bipyridine ligand with high enantiospecificity. a-Aminobenzylboronates bearing fully substituted boron-bound stereogenic centers also gave the 3,3-disubstituted isoindolinones with stereospecific stereochemical inversion in the presence of simple 2,2'-bipyridine as a ligand.Cross-coupling reactions to form stereogenic sp 3 -carbon centers [1] are recognized as a highly attractive transformations in asymmetric synthesis. Most typically, enantioenriched or racemic chiral secondary alkyl electrophiles are used in the coupling with achiral organometallic reactants, leading to stereospecific [2] or enantioconvergent [3] cross-coupling. In addition to such coupling using chiral electrophiles, stereospecific cross-couplings using configurationally stable chiral organometallic compounds [4][5][6][7] have gained increasing attention. Particular attention is paid to Suzuki-Miyaura-type, that is, boron-based, cross-coupling of enantioenriched alkylboronates (Figure 1 a). Such reactions are highly attractive because the starting enantioenriched organoborons are configurationally robust and easily accessible by asymmetric hydroboration and related transformation. [8][9][10][11] The reaction course of the cross-coupling process can be switched from stereochemically retentive to invertive, thereby allowing the reaction to afford either enantiomer even from single enantiomers of starting organoboron compounds. However, such boron-based stereospecific coupling processes have so far been limited to palladium-catalyzed reactions using organoboron compounds bearing a boron-bound trisubstituted stereogenic carbon center. To our knowledge, there has been no precedent for stereospecific cross-coupling at fully substituted metal-bound stereogenic carbons to date.During the course of our study of the stereospecific crosscoupling of a-aminoalkylboronic acid derivatives, [7b,d,h] a report from the Dumas group caught our attention: a-[(obromobenzoyl)amino]benzylboronates undergo intramolecular cross-coupling to form 3-arylisoindolinones in the presence of a 2,2'-bipyridine/copper(II) catalyst (Figure 1 b). [12] This intramolecular reaction appears to highly valuable synthetically because, even though it is a simple cyclization, the substrates can be synthesized through the coupling of two easily available components, that is, a-aminoalkylboronic acids and o-haloaroyl chlorides, through an amidation reaction. Although the report claimed that complete racemization was observed in a reaction of enantiopure a-[(o-bromobenzoyl)amino]benzylboronates under standard reaction conditions, we decided to examine this potentially useful synthetic transforma...

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Enantiospecific intramolecular Suzuki–Miyaura‐type coupling with α‐(2‐halobenzoylamino)benzylboronic esters to give 3‐substituted isoindolinones is achieved by using copper catalysts with 2,2′‐bipyridine‐based achiral ligands. Enantioenriched α‐aminobenzylboron reactants bearing a hydrogen atom at the boron‐bound stereogenic carbons undergo stereoinvertive coupling in the presence of a 6‐phenyl‐2,2′‐bipyridine ligand with high enantiospecificity. α‐Aminobenzylboronates bearing fully substituted boron‐bound stereogenic centers also gave the 3,3‐disubstituted isoindolinones with stereospecific stereochemical inversion in the presence of simple 2,2′‐bipyridine as a ligand.