Kinetic Resolution Of Terminal Epoxides Research Articles

ChemInform Abstract: Hydrolytic Kinetic Resolution of Terminal Epoxides Catalyzed by Novel Bimetallic Chiral Co (Salen) Compounds.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Polyglycerol‐Supported Co‐ and Mn‐Salen Complexes as Efficient and Recyclable Homogeneous Catalysts for the Hydrolytic Kinetic Resolution of Terminal Epoxides and Asymmetric Olefin Epoxidation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Chiral cobalt salen complexes containing Lewis acid: A highly reactive and enantioselective catalyst for the hydrolytic kinetic resolution of terminal epoxides

A type of chiral salen complexes bearing Lewis acid, including FeCl3, AlCl3, ZnCl2, and SnCl4 has been synthesized. The prepared complexes proved to be reactive and enantioselective in the hydrolytic kinetic resolution of terminal epoxides. The catalysts could be recovered and reused several times with simple treatment after reaction, without loss of activity and enantioselectivity. (salen)Co(II) and Lewis acid in mol ratios of 1: 1, 1: 2, and 1: 3 showed the same activity, enatioselectivity, and stability. The characterization of the complexes in-situ generated by the reaction of (salen)Co(II) and Lewis acid in mol ratios of 1: 1, 1: 2, and 1: 3 in CH2Cl2 was performed by UV-Vis, which showed an identical spectrum and did not display any change along with the time prolonged. Thus, the present catalysts can be applicable for large scale processes for HKR reaction of racemic epoxides.

Asymmetric catalysis by chiral salen complexes immobilized on mesoporous materials having modified pore channel system by dimethylcarbonate

The mesoporous materials having bimodal pore structure were synthesized by treatment of dimethylcarbonate (DMC) in the presence of metal salts as a catalyst. The pore system was characterized by BET, TEM analysis and by comparing the catalytic activity under the same conditions. The chiral (salen) Co-MX3 immobilized on SBA-15 and MCM-48 which were partially desilylated by DMC showed higher activity for the enantioselective kinetic resolution of terminal epoxides with H2O and phenols, relative to original SBA-15 and MCM-48 having regular pore channels. The heterogeneous catalysts can offer practical advantages of the facile separation from reactants and products, as well as recovery and reuse.

Polyglycerol‐Supported Co‐ and Mn‐salen Complexes as Efficient and Recyclable Homogeneous Catalysts for the Hydrolytic Kinetic Resolution of Terminal Epoxides and Asymmetric Olefin Epoxidation

AbstractIn this report we demonstrate the suitability of hyperbranched polyglycerol as high‐loading support for asymmetric catalysis. A polyglycerol‐supported unsymmetrical salen ligand was prepared and purified by means of ultrafiltration. The polymeric ligand was metalated with cobalt acetate to afford the corresponding supported Co‐salen complex which was further utilized in the hydrolytic kinetic resolution (HKR) of terminal epoxides. Kinetic studies for HKR of 1,2‐epoxyhexane using polyglycerol‐supported Co‐salen showed improved catalytic performance compared to the respective non‐immobilized catalyst. This observation points to the presence of a positive dendrimeric effect assuming a cooperative bimetallic mechanism. Furthermore, a polymer‐supported Mn‐salen catalyst was prepared and successfully applied in the asymmetric epoxidation of olefins. The respective dendritic catalyst was recycled by precipitation up to three times in the epoxidation of 6‐cyano‐2,2‐dimethylchromene (ee up to 95 %). Experiments with repetitive batches revealed enhanced stability of the catalyst as a result of immobilization whereby the total turnover number increased from 23 in a single batch to around 80 for four repetitive batches. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Hydrolytic Kinetic Resolution of Terminal Epoxides catalyzed by Novel Bimetallic Chiral Co (Salen) Complexes

Novel bimetallic chiral Co (salen) complexes bearing transition‐metal salts have been synthesized. The easily prepared complexes exhibited very high catalytic reactivity and enantioselectivity in hydrolytic kinetic resolution (HKR) of racemic terminal epoxides and consequently provided enantiomerically enriched epoxides (up to 99% ee).

Asymmetric synthesis of α-aryloxy alcohols via kinetic resolution of terminal epoxides catalyzed by (R,R)-N,N′-bis(2-hydroxy-5-tert-butylsalisilidine)-1,2-cyclohexenediamino cobalt

New chiral Co-salen complexes with tert-butyl group in position 5 of the aromatic ring in the structure have been synthesized and they were applied as a chiral catalyst. A dimeric chiral salen having a transition metal salt such as AlCl3, displayed very high catalytic reactivity and enantioselectivity for the asymmetric ring opening of epoxides to synthesize optically pure α-aryloxy alcohols via phenolic kinetic resolution.

Continuous Enantioselective Kinetic Resolution of Terminal Epoxides Using Immobilized Chiral Cobalt—Salen Complexes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Kinetic resolution of terminal epoxides with phenols promoted by heterometallic Co–Al and Co–Ga salen complexes

The binuclear chiral (salen) Co complexes bearing Lewis acid salt (Al and Ga) and 4-nitrobenzene sulfonic acid (NBS) catalyze the enantioselective ring opening of terminal epoxides with phenol derivatives. The easily prepared complexes exhibited very high catalytic reactivity and enantioselectivity for the asymmetric ring opening of terminal epoxides with phenol and consequently provide enantiomerically enriched corresponding α-aryloxy alcohols (up to >99% ee). The two unit of salen complexes combined by Lewis acid exhibited co-operative catalysis during the ring opening reaction.

Oxidatively pure chiral (salen)Co(III)-X complexes in situ prepared by Lewis acid-promoted electron transfer from chiral (salen)Co(II) to oxygen: Their application in the hydrolytic kinetic resolution of terminal epoxides

The Lewis acid (MX 3)-promoted oxidation of chiral (salen)Co(II) complex afforded neither the mononuclear nor dinuclear heterobimetallic chiral (salen)Co complexes, such as [(salen)Co(III)-X]⋯MX 3 or [(salen)Co(III)-X] 2⋯MX 3, as reported in the literatures, but rather the Jacobsen's complexes, chiral (salen)Co(III)-X. The chiral (salen)Co(III)-X complexes in situ generated by the reaction of MX 3 and (salen)Co(II) in molar ratio of 1:3 were shown to have identical catalytic properties in the hydrolytic kinetic resolution (HKR) reactions of racemic epoxides, in terms of activity, enantioselectivity and stability, to those of the purified (salen)Co(III)-X complex. This result strongly indicates that metallic residues of Lewis acids (e.g., metal oxide residues) remained in the reaction mixture did not display any negative influence on the catalytic efficiencies. Thus, the present in situ method for catalyst activation can be applicable for large scale process for HKR reactions of racemic epoxides.

Enantioselective synthesis of ( S)-timolol via kinetic resolution of terminal epoxides and dihydroxylation of allylamines

An efficient enantioselective synthesis of ( S)-timolol has been described using chiral Co–salen-catalyzed kinetic resolution of less expensive (±)-epichlorohydrin with 3-hydroxy-4-( N-morpholino)-1,2,5-thiadiazole in good overall yield (55%) and excellent enantioselectivity (98%). Synthesis of ( S)-timolol has also been achieved using hydrolytic kinetic resolution as well as asymmetric dihydroxylation routes in 90% ee and 56% ee, respectively.

Continuous Enantioselective Kinetic Resolution of Terminal Epoxides Using Immobilized Chiral Cobalt-Salen Complexes

Jacobsen’s cobalt-salen complex was covalently immobilized on polymer carriers that are part of different technical setups (polymer powder, composite Raschig rings, PASSflow microreactors) and employed for the enantioselective ring opening of terminal epoxides with water and phenols. The polymer-supported catalysts showed good activity and stereoselectivity and could be used repeatedly after a simple reactivation protocol in both batch as well as continuous-flow modes.

Concise synthesis of β-blockers ( S)-metoprolol and ( S)-betaxolol using hydrolytic kinetic resolution

Enantiopure ( S)-metoprolol and ( S)-betaxolol were prepared in an extremely simple and practical way using Jacobsen's hydrolytic kinetic resolution of terminal epoxides in isopropanol.

Microwave-assisted Cr(salen)-catalysed asymmetric ring opening of epoxides

The effect of microwaves on the kinetics and the selectivity of the Cr(salen)-catalysed asymmetric ring opening of epoxides was investigated. It was found that the reaction rate of the Cr(salen)-catalysed kinetic resolution of terminal epoxides and the asymmetric ring opening (ARO) of meso-epoxides could be increased by three orders of magnitude without impairing the selectivity.

Highly reactive and enantioselective kinetic resolution of terminal epoxides with H 2O and HCl catalyzed by new chiral (salen)Co complex linked with Al

The asymmetric hydrolytic kinetic resolution (HKR) of racemic terminal epoxides by new easily synthesized dimeric chiral (salen)Co bearing Al, provides a practical and straightforward method for the synthesis of enantiomerically enriched terminal epoxides (>99% ee) and diols. An inorganic acid, HCl is applied first time for the asymmetric ring opening reaction of terminal epoxides. Reactions are conveniently carried out at room temperature under an air atmosphere.

New Oligomeric Catalyst for the Hydrolytic Kinetic Resolution of Terminal Epoxides under Solvent‐Free Conditions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Mechanistic investigation leads to a synthetic improvement in the hydrolytic kinetic resolution of terminal epoxides.

The mechanism of the hydrolytic kinetic resolution (HKR) of terminal epoxides was investigated by kinetic analysis using reaction calorimetry. The chiral (salen)Co-X complex (X = OAc, OTs, Cl) undergoes irreversible conversion to (salen)Co-OH during the course of the HKR and thus serves as both precatalyst and cocatalyst in a cooperative bimetallic catalytic mechanism. This insight led to the identification of more active catalysts for the HKR of synthetically useful terminal epoxides.

Fluorous biphasic hydrolytic kinetic resolution of terminal epoxides

Although application of light-fluorous techniques facilitates the isolation of reaction products from the hydrolytic kinetic resolution (HKR) of terminal epoxides catalysed by cobalt complexes of salen ligands, the extension of the original fluorous biphasic approach to this reaction is far from being a trivial exercise. The nature of the counter anion has a dramatic effect on the catalytic activity of heavily fluorinated chiral (salen) cobalt(III) complexes. Excellent enantioselectivities are obtained in the fluorous biphasic HKR of 1,2-hexene oxide when fluorinated anions are introduced (e.e.s up to 99% both for the diol and the epoxide), with C 8F 17COO – affording reaction rates even higher than those observed with non-fluorous systems.

New oligomeric catalyst for the hydrolytic kinetic resolution of terminal epoxides under solvent-free conditions

The solvent-free hydrolytic kinetic resolution of terminal epoxides catalyzed by a new oligomeric (salen)Co complex 2 is described. Extremely low loadings of catalyst were used to provide all epoxides examined in good yields and >99% ee under ambient conditions within 24 h.

Hydrolytic Kinetic Resolution of Terminal Epoxides Catalyzed by Fluorous Chiral Co(salen) Complexes.

AbstractFor Abstract see ChemInform Abstract in Full Text.