Chiral Polymer Catalysts Research Articles

Development of Dynamically Chiral Helical Polymer Catalysts Based on Post-Polymerization Modification of Boronyl Pendants

Catalytic asymmetric synthesis is one of the most efficient methods for the preparation of chiral compounds with high optical purity. Although a variety of robust chiral scaffolds have been developed to achieve efficient chiral catalysts which show high catalytic activities and stereoselectivities, use of dynamic chiral scaffold is desired for the development of advanced chiral catalysts featuring stimuli-responsive properties such as chirality-switching and asymmetric amplification. We have developed chirality-switchable helical polymer ligands bearing monodentate phosphine pendants, which exhibit high enantioselectivities based on solvent-dependent dynamic screw-sense control of poly(quinoxaline-2,3-diyl)s (PQXs) having chiral side chains. However, the application has been limited to palladium-catalyzed asymmetric reactions. This article describes the development of helically chiral polymer catalysts based on post-polymerization modification of bornyl pendants (-B(OH)2) attached to the PQXs. Introduction of 2,2′-bipyridine pendants to chiral PQXs through Suzuki-Miyaura coupling at the boronyl pendants led to the development of chirality-switchable helical polymer ligands for copper-catalyzed asymmetric reactions. In addition, introduction of 4-aminopyridine pendants into the chiral PQXs provided chirality-switchable efficient asymmetric nucleophilic catalysts for kinetic resolution of secondary alcohols and asymmetric Steglich-type acyl rearrangements. Furthermore, by using the boronyl pendants as molecular recognition sites for screw-sense induction to achiral PQXs, a chiral-guest-responsive helical polymer ligand bearing monodentate phosphine pendants was developed for the palladium-catalyzed asymmetric reaction. Using an amino alcohol as a chiral additive, the screw-sense induction proceeded with asymmetric amplification, giving the corresponding product with higher optical purity than that of the chiral additive.

キラル高分子触媒の合成と不斉反応への応用

キラル高分子触媒の合成と不斉反応への応用

Synthesis of Cinchona Alkaloid-Derived Chiral Polymers by Mizoroki–Heck Polymerization and Their Application to Asymmetric Catalysis

To facilitate the asymmetric catalysis process, we designed novel polymeric chiral catalysts. Since quaternary ammonium salts of cinchona alkaloid derivatives show efficient catalytic activity in various asymmetric transformations, we have synthesized novel chiral polymer catalysts containing cinchonidinium moieties in the main chain of the polymer. Repetitive Mizoroki–Heck coupling reactions between the cinchona alkaloid-derived dimer and diiodide afforded the chiral polymer catalysts, which were subsequently used as catalysts in asymmetric benzylation reactions to yield the corresponding phenylalanine derivatives in higher yields and levels of enantioselectivity than can be obtained with a monomeric catalyst. Because of the insolubility of the polymeric catalysts, they were easily recovered from the reaction mixture and reused several times.

ChemInform Abstract: Enantioselective Addition of Diethylzinc to Aldehydes Using Chiral Polymer Catalysts Possessing a Methylene Spacer.

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ChemInform Abstract: Heterogeneous Asymmetric Addition of Diethylzinc to Aromatic Aldehydes Catalyzed by Ti(IV)/Imine Bridged Poly(R)-binaphthol.

Abstract Heterogeneous asymmetric addition of diethylzinc to aldehydes catalyzed by chiral polymer catalysts has been achieved. The conjugated polymers based on a BINOL skeleton were synthesized in five steps and applied to this reaction with yield and e.e. up to 95 and 84.5%, respectively. These chiral polymers can be easily quantitatively recovered and reused without decreasing of e.e. or catalytic activity.

Heterogeneous asymmetric addition of diethylzinc to aromatic aldehydes catalyzed by Ti(IV)/imine bridged poly( R)-binaphthol

Heterogeneous asymmetric addition of diethylzinc to aldehydes catalyzed by chiral polymer catalysts has been achieved. The conjugated polymers based on a BINOL skeleton were synthesized in five steps and applied to this reaction with yield and e.e. up to 95 and 84.5%, respectively. These chiral polymers can be easily quantitatively recovered and reused without decreasing of e.e. or catalytic activity.

Asymmetric catalysis on solids

The processing advantages associated with heterogeneous catalysis have led to the development of many new chiral heterogeneous catalysts for a variety of important asymmetric reactions. Established systems, such as chirally modified metals, have been further developed, while new strategies for the creation of chiral polymer catalysts and oxide systems, such as zeolites containing chelate complexes, are being explored. Important issues, such as site isolation, stability against leaching, and mass transfer to the active sites, have been addressed. Advances have been made in chiral zeolite frameworks and porous hybrid solids, chiral modifiers in porous hosts, asymmetric catalysts occluded in membranes and dissolved in supported liquid films, and modular chelate complexes on polymer beads.

Recent developments in asymmetric catalysis using synthetic polymers with main chain chirality

Some recent developments in the use of main chain chiral polymer catalysts are summarized. These polymers are different from the traditional polymer catalysts that are prepared by anchoring monomeric chiral catalysts to an achiral polymer backbone. Three classes of synthetic main chain chiral polymers are discussed including: (1) helical polymers represented by polypeptides; (2) polymers with flexible chiral chains such as polyesters and polyamides; and (3) polymers of rigid and sterically regular chiral chains represented by chiral conjugated polybinaphthyls. Some of these polymer catalysts have shown high enantioselectivity in asymmetric organic transformations.

Enantioselective addition of diethylzinc to aldehydes using chiral polymer catalysts possessing a methylene spacer

N-Butylnorephedrine supported on polystyrene resin via a six-methylene spacer catalyses the enantioselective addition of diethylzinc to both aromatic and aliphatic aldehydes, providing optically active secondary alcohols in good to high enantiomeric excesses. In the enantioselective addition of diethylzinc to an aliphatic aldehyde, polymer catalyst with a six-methylene spacer is more enantioselective than other previously reported polymer catalysts.

Chiral polymer catalysts in preparative organic chemistry—A critical overview: E. Chiellini, University of Pisa, Pisa, Italy

Chiral polymer catalysts in preparative organic chemistry—A critical overview: E. Chiellini, University of Pisa, Pisa, Italy

ChemInform Abstract: Chiral Polymer Catalysts in Preparative Organic Chemistry: A Critical Overview

ChemInformVolume 19, Issue 30 Reviews ChemInform Abstract: Chiral Polymer Catalysts in Preparative Organic Chemistry: A Critical Overview M. AGLIETTO, M. AGLIETTO Dip. Chim. Ind., Univ., Pisa, ItalySearch for more papers by this authorE. CHIELLINI, E. CHIELLINI Dip. Chim. Ind., Univ., Pisa, ItalySearch for more papers by this authorS. D'ANTONE, S. D'ANTONE Dip. Chim. Ind., Univ., Pisa, ItalySearch for more papers by this authorG. RUGGERI, G. RUGGERI Dip. Chim. Ind., Univ., Pisa, ItalySearch for more papers by this authorR. SOLARO, R. SOLARO Dip. Chim. Ind., Univ., Pisa, ItalySearch for more papers by this author M. AGLIETTO, M. AGLIETTO Dip. Chim. Ind., Univ., Pisa, ItalySearch for more papers by this authorE. CHIELLINI, E. CHIELLINI Dip. Chim. Ind., Univ., Pisa, ItalySearch for more papers by this authorS. D'ANTONE, S. D'ANTONE Dip. Chim. Ind., Univ., Pisa, ItalySearch for more papers by this authorG. RUGGERI, G. RUGGERI Dip. Chim. Ind., Univ., Pisa, ItalySearch for more papers by this authorR. SOLARO, R. SOLARO Dip. Chim. Ind., Univ., Pisa, ItalySearch for more papers by this author First published: July 26, 1988 https://doi.org/10.1002/chin.198830370Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume19, Issue30July 26, 1988 RelatedInformation

Chiral polymer catalysts in preparative organic chemistry: a critical overview

Abstract