Asymmetric Epoxidation of α,β-Unsaturated Ketones Catalyzed by Chiral Polybinaphthyl Zinc Complexes:  Greatly Enhanced Enantioselectivity by a Cooperation of the Catalytic Sites in a Polymer Chain

Abstract

Polybinaphthyl zinc catalysts have been developed for the asymmetric epoxidation of alpha,beta-unsaturated ketones in the presence of tert-butyl hydroperoxide. Up to 81% ee has been achieved for the epoxidation of alpha,beta-unsaturated ketones containing beta-aliphatic substituents by using a binaphthyl polymer combined with diethylzinc. A very interesting positive cooperative effect of the catalytic sites in the polymer chain is observed which leads to greatly increased enantioselectivity over the corresponding monomer ligands.

Three‐Membered Heterocycles. Structure and Reactivity

“…This protocol was used as a key step in the synthesis of ( þ )-decursin from commercially available esculetin [500]. Solidsupported catalysts have also been reported, including the complex formed by treating binaphthyl polymers (e.g., 452) with diethyl zinc [501].…”

Optically Active Polymer and Dendrimer Synthesis and their Use in Asymmetric Catalysis

“…The 3,3 0 -and 6,6 0 -linked BINOL-based polymers were used for the asymmetric epoxidation of a,b-unsaturated ketones to generate chiral a,b-epoxy ketones (Scheme 11.12) [18].…”

“…Incorporating this chiral unit into a polymer backbone creates a new family of polymers with stable main chain chirality [7][8][9][10][11][12][13]. Depending on how BINOL units are linked in the polymer systems, the BINOLbased polymers can be generalized as the 6,6 0 -linked (major groove) or 3,3 0 -linked (minor-groove) polymers.…”

“…Because of the introduction of the flexible hexyl groups, (R)-11.5 was soluble in common organic solvents such as THF, toluene, and CH 2 Cl 2 . Scheme 11.3 shows the synthesis of another 6,6 0 -linked polyBINOL (S)-11.7 [8]. Monomer (S)-11.6 containing two different protecting groups was polymerized with the diboronic acid 11.4a.…”

Synthesis and Characterization of Polybinaphthyls Incorporating Chiral (R) or (S)-2,2′-Binaphthyl Entities by Heck Reaction

“…The 2,2 0 -hydroxyl groups of BINOL can be easily converted into other functional groups and the 3,3 0 -and 6,6 0 -positions of binaphthyl skeletal structure of BINOL can be selectively functionalized at the well-defined molecular level, leading to a variety of binaphthyl derivatives which can exhibit remarkably stable chiral configuration as well as high chiral induction in molecular recognition, [5][6][7][8][9] asymmetric processes. [10][11][12][13][14][15] These rigid and sterically chiral polybinaphthyl polymers also represent a new generation of materials for applications in chiral sensors, polarized light emission and nonlinear optical materials. [16][17][18][19][20] Conjugated polymers with rigid -systems often possess poor solubility, which seriously inhibits full structural elucidations and property investigations.…”