Enantioconvergent Cu-Catalyzed Intramolecular C–C Coupling at Boron-Bound C(sp³) Atoms of α-Aminoalkylboronates Using a C₁-Symmetrical 2,2′-Bipyridyl Ligand Attached to a Helically Chiral Macromolecular Scaffold

Abstract

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.

Asymmetric hydroamination with far fewer chiral species than copper centers achieved by tuning the structure of supramolecular helical catalysts

“…15,16 Examples of S&S-type asymmetric catalysts have mainly been reported for helical covalent polymers, 17,18 the most potent ones being based on the poly(quinoxaline-2,3-diyl) (PQX) scaffold. 14,19,20 PQX helical catalysts appended with phosphine ligands were found to provide excellent enantioselectivities in a range of palladium-catalysed reactions, whilst nitrogen-containing PQXs were employed in copper-mediated 21,22 and organocatalytic processes. 23–25 PQX catalysts reported to date either consisted of copolymers embedding a large of fraction of chiral monomers (95%) 26–32 or on terpolymers containing an additional achiral monomer acting as “spacer” between the catalytic unit, 33–36 and for which, the “sergeants” are actually in excess relatively to the catalytic units.…”

Emergence of Highly Enantioselective Catalytic Activity in a Helical Polymer Mediated by Deracemization of Racemic Pendants

“…Since the pioneering studies by Reggelin et al, , various one-handed helical polymer-based asymmetric catalysts have been developed ,, by the helix-sense-selective polymerization of achiral monomers bearing a catalytically active or metal-binding site, , their copolymerization with chiral monomers, − or homopolymerization of catalytically active chiral monomers. − Some of them have produced optically active products with excellent enantioselectivity of more than 90% enantiomeric excess (ee). − ,− Suginome and co-workers discovered that the chirality ( R or S ) of the asymmetric reaction products can be switched in different solvents using a single helical polymeric catalyst composed of dynamic helical chiral/achiral copolymers of 1,2-diisocyanobenzenes, while maintaining the high enantioselectivity resulting from the solvent-induced reversible helix inversion − ,, of the copolymer backbones. ,,, However, the use of nonracemic monomers, which contributes to the helical sense bias, is of primary importance for enantioselective catalysis. ,, …”

A Versatile Method for the End‐Functionalization of Polycarbenes

“…[19][20][21][22] Indeed, these polymers are widely used in our modern life. [23] As recently reported by Wu's research group, optically active helical polycarbenes can be obtained using a series of chiral Pd(II) catalysts bearing a rigid phosphine moiety. [24] The helical polycarbenes thus obtained were observed to bear quite stable and hard-to-remove Pd(II)complexes at the end of each chain.…”