Ring Opening Of Terminal Epoxides Research Articles

Mechanochemical synthesis of unsymmetrical salens for the preparation of Co-salen complexes and their evaluation as catalysts for the synthesis of α-aryloxy alcohols via asymmetric phenolic kinetic resolution of terminal epoxides.

In this paper, we report the mechanochemical synthesis of unsymmetrical salens using grinding and ball milling technologies, respectively, both of which were afforded in good yield. The chelating effect of the unsymmetrical salens with zinc, copper, and cobalt was studied and the chiral Co–salen complex 2f was obtained in 98% yield. Hydrolytic kinetic resolution (HKR) of epichlorohydrin with water catalyzed by complex 2f (0.5 mol %) was explored and resulted in 98% ee, suggesting complex 2f could serve as an enantioselective catalyst for the asymmetric ring opening of terminal epoxides by phenols. A library of α-aryloxy alcohols 3 was thereafter synthesized in good yield and high ee using 2f via the phenolic KR of epichlorohydrin.

Simple Trivalent Cobalt Complex-Mediated Copolymerization of Epoxides with Isocyanate: Combining High Activity and Selectivity

Controlled ring-opening copolymerization involving epoxides represents a valuable strategy for the synthesis of oxygenated polymers with unique biodegradability and biocompatibility. In this study, simple trivalent metal complexes, salenM(III)X (salen = N,N′-bis(salicylidine) diamine derivatives, M = Al, Cr, and Co), are employed for copolymerizing p-tosyl isocyanate (TSI) with epoxides, generating perfectly alternating polyurethanes with various structures and tunable properties. The trivalent cobalt acetate complex of N,N′-bis(salicylidine)-o-phenylenediamine bearing 3- and 3′-, 5- and 5′-tert-butyl groups exhibited the highest activity of up to 41,400 h–1 under mild conditions. This single-site catalyst also showed excellent activity and selectivity for copolymer formation even at an extremely low loading of 0.002 mol % without any cocatalyst activator and operated efficiently for various terminal epoxides, affording completely alternating polyurethanes with high molecular weights and narrow polydispersities. Also, this catalyst was tolerant of large quantities of chain transfer agents, thereby allowing control of the molecular weight. Notably, the ring opening of terminal epoxides predominantly occurring at the methylene C–O bond resulted in the formation of stereoregular polyurethanes with more than 96% head-to-tail content.

Base-mediated synthesis of benzimidazole-fused 1,4-benzoxazepines via sequential intermolecular epoxide ring-opening/intramolecular SNAr reactions

We have developed a transition-metal-free, practical route to benzimidazole-fused 1,4-benzoxazepines. Operationally, the protocol involves a K2CO3-mediated intermolecular ring opening of terminal epoxides by 2-(2-fluorophenyl)benzimidazole, followed by an intramolecular nucleophilic aromatic substitution (SNAr) reaction of the resulting products in the presence of NaH. We have also achieved an 11-step synthesis of a chroman-linked benzimidazole-fused 1,4-benzoxazepine using a phenoxide-ion induced 6-exo intramolecular epoxide ring-opening and an alkoxide-ion induced intramolecular SNAr reaction as key steps.

CO2 Adducts of Phosphorus Ylides: Highly Active Organocatalysts for Carbon Dioxide Transformation

A series of phosphorus ylide (P-ylide) CO2 adducts were synthesized and first used as organocatalysts for CO2 transformation. Detailed studies on the cycloaddition reaction of CO2 with terminal epoxides show that P-ylide CO2 adducts are efficient metal-free and halogen-free organocatalysts to mediate this reaction under ambient conditions (25 °C, 1 atm of CO2). More importantly, the reactions proceeded with a broad scope, high efficiency, and good functional group tolerance and the corresponding cyclic carbonate products were obtained in good to excellent yields (46–99%). Meanwhile, the kinetic study by in situ FTIR methods suggested an intermolecular cooperation effect for effectively accelerating the ring opening of terminal epoxides. Furthermore, from an investigation of the catalytic diversity of P-ylide CO2 adducts, CO2 also could be converted to functionalized cyclic α-alkylidene carbonates, oxazolidinone, and N-methylated and N-formylated amines by organocatalytic reactions.

메조세공 BEA에 고정화된 키랄 Co살렌 착체의 동적분할을 통한 고광학순도의 키랄 모노에스테르 합성

BEA형 제올라이트를 알칼리용액으로 처리하여 결정구조 내에 메조세공이 형성되도록 제조하고, 세공 내에 균일계 키랄 Co(III) 살렌을 고정화시켰다. 메조세공 BEA-제올라이트에 고정화된 이핵형 Co-<TEX>$GaCl_3$</TEX> 살렌 촉매는 말단 에폭사이드의 산소고리를 카르복실산으로 여는 키랄 반응에 대하여 높은 활성을 나타내었다. 이 반응을 통하여 라세믹 에폭사이드로부터 다양한 모노 에스테르 유도체를 중간 정도의 광학선택도(47~69 ee%)로 합성할 수 있었다. 키랄(S)-ECH를 반응물로 사용하면, 이들은 키랄 살렌 촉매 존재하에서 카르복시 산에 의하여 에폭사이드의 링이 광학선택적으로 열리며, 생성된 화합물을 염기용액에서 탈염산 처리하면 다시 에폭사이드 링이 형성되면서 광학순도가 매우 높은 모노에스터 에폭사이드 (R)-GB (98 ee% 이상)가 얻어졌다. 고정화촉매는 매우 용이하게 제조될 수 있었으며, 특별한 재생처리 없이 여러번 재사용하여도 촉매의 활성이 유지되었다. BEA-zeolite was modified by alkaline solution to introduce mesoporosity in the crystals and the homogeneous chiral Co(III) salen was immobilized in the mesopores. The dinuclear chiral Co(salen)-<TEX>$GaCl_3$</TEX> catalyst immobilized on mesoporous BEA-zeolite showed high activity for the regioselective ring opening of terminal epoxides by carboxylic acids. Various chiral monoester derivatives could be synthesized with moderate enantioselectivity (47~69 ee%) from racemic epoxides through above reaction. When the chiral (S)-ECH was used as a reactant, it was efficiently resolved by carboxylic acid with a high enantioselectivity in the presence of heterogenized chiral salen catalyst, and the ring opened product afforded optically pure monoester epoxide (R)-GB (up to 98 ee%) through the ring closing in the basic solution by elimination of HCl. The heterogeneous catalyst could be fabricated easily, and the catalytic activity was retained for several times reuse without any further regeneration step.

Bioglycerol-based Sulphonic Acid Functionalized Carbon: An Efficient and Recyclable, Solid Acid Catalyst for the Regioselective Azidolysis of Epoxides in Aqueous Acetonitrile

A convinent and efficient method was developed for the synthesis of 1,2-azidoalcohols by ring opening of terminal epoxides with sodium azide employing glycerol-based sulphonic acid functionalized carbon as heterogeneous catalyst in aqueous acetonitrile. The reaction is highly regioselective and affords the corresponding products in excellent yields (78-100%) under mild reaction conditions. The catalyst exhibited efficient reusability without loosing its activity even after 5 cycles of azidolysis of methyl 10,11-epoxy undecanoate under optimized conditions within 2 h.

Masked amino acid: a new C-nucleophile for I2-catalyzed stereoselective ring opening of epoxides in ionic liquid

The first one-pot molecular iodine catalyzed direct aminoacetylation of terminal epoxides in ionic liquid [bmim]OH is reported. Herein, 2-phenyl-1,3-oxazolon-5-one and a variety of terminal epoxides afford 3-(N-substituted)aminofuran-2-ones in high yield (84–95%) and excellent cis diastereoselectivity (>94%) via ring-opening of terminal epoxides and aminoacetylative cyclization cascade. Operation simplicity, absence of by-product formation, and ambient temperature are the salient features of the present synthetic protocol. After isolation of the product, the ionic liquid [bmim]OH could be easily recycled for further use without any loss of efficiency.

Catalytic Regioselective Epoxide Ring Opening with Phenol Using Homogeneous and Supported Analogues of Dimethylaminopyridine

The regioselective ring opening of terminal epoxides using phenolic nucleophiles is examined using dimethylaminopyridine (DMAP) as a soluble catalyst and solid catalysts based on silica, polymer, and magnetic nanoparticle solids functionalized with DMAP analogues. The homogeneous reaction proceeds to 94 % conversion while achieving 93 % regioselectivity in 2 h at 120 °C. DMAP efficiently catalyzes the ring-opening reaction of a variety of epoxides using different substituted phenols with high conversions and excellent regioselectivities. Of the heterogeneous catalysts, the polymeric catalyst is more active and recyclable than the magnetic nanoparticle and silica supported catalysts, which had comparable activity and recyclability.

Asymmetric ring opening of terminal epoxides via kinetic resolution catalyzed by chiral (salen)Co mixture

The highly enantioselective hydrolytic kinetic resolution (HKR) of racemic terminal epoxides by bimetallic chiral (salen)Co and (salen)Co(III)-OAc mixture provides a simple and effective method for the synthesis of enantiomerically enriched terminal epoxides (ee > 99%) and diols. At the equimolar amounts of bimetallic chiral (salen)Co and (salen)Co(II)-OAc, the catalytic activity increases more than two times in comparison with (salen)Co(III)-OAc used alone. The mixed catalytic system can be recycled and reused. No significant loss of catalytic activity was observed after three runs.

Highly active oligomeric Co(salen) catalysts for the asymmetric synthesis of α-aryloxy or α-alkoxy alcohols via kinetic resolution of terminal epoxides

A mixture of Co(salen) macrocycles, prepared via the ring expansion metathesis oligomerization of salen-functionalized cyclooctene monomers, among the most active soluble catalysts for the hydrolytic kinetic resolution (HKR) of terminal epoxides, is exploited as the catalyst in the ring-opening of epoxides using aliphatic alcohols or phenols as nucleophiles, leading to the direct synthesis of optically active α-aryloxy alcohols or α-alkoxy alcohols. The catalyst is compared to other dimeric, oligomeric and monomeric Co(salen) complexes including a pimelate-linked macrocyclic Co(salen) catalyst and a dimeric Co(salen) catalyst referred to as a bisalen. The catalysts that contain multiple Co(salen) units within a single molecular framework allow for substantial decreases in catalyst loading compared with the monomeric catalyst. The cyclooctene-based Co(salen) macrocycle catalyst allows for good activity and enantioselectivity in the ring-opening of terminal epoxides with phenols as nucleophiles, giving enhanced turnover frequencies relative to many literature catalysts. The cyclooctene-based Co(salen) macrocycle catalyst and the bisalen catalysts are shown to be the most active in the asymmetric ring-opening of (±)1,2-epoxyhexane with methanol, out-performing the other catalysts tested. The Co(salen) macrocycle catalyst is recycled 3 times in this reaction with some loss in activity but no noteworthy change in selectivity.

Asymmetric Ring Opening of Terminal Epoxides Catalyzed by Chiral Co(III)-BF3Salen Complex Immobilized on SBA-16

The homogeneous BF3 containing chiral Co(III) salen complexes were anchored non-covalently on the surfaces of mesoporous SBA-16 silica containing aluminum species. The Bronsted and Lewis acidic sites are attributed to the immobilization of fluorine functionalized chiral salen complexes on the supports. The FT-IR, UV, ESCA, and NMR analyses were performed to determine the structure of synthesized chiral salen catalysts. These heterogeneous catalysts could be applied in asymmetric ring opening of terminal epoxides by water and phenol derivatives. They showed very high enantioselectivity and yield more than 98% in the catalytic synthesis of optically active products.

Non-Covalent Immobilization of Chiral (Salen) Complexes on HF-treated Mesoporous MFI-type Zeolite for Asymmetric Catalysis

MFI structural zeolite (ZSM-5 or Sililcalite) was treated with HF solution to introduce mesoporous channels in the microporous crystals. Inner mesopore size could be controlled from 2.5 to 3.5 nm by changing the concentration of HF solution. The pore structure of HF-treated MFI zeolite was studied by instrumental analysis. The active Co (III) salen complex monomers were successfully anchored non-covalently on the surfaces of mesoporous MFI-type zeolite. These heterogeneous catalysts could be applied in asymmetric ring opening of terminal epoxides by phenol derivatives. It showed very high enantioselectivity and yield up to 95% in the catalytic synthesis of optically active <TEX>$\alpha$</TEX>-aryloxy alcohol compounds.

Chiral (Salen) Cobalt Complexes Encapsulated in Mesoporous MFI as an Enantioselective Catalyst for Asymmetric Ring Opening of Terminal Epoxides

MFI structural zeolite (ZSM-5 and Sililcalite) was treated with hot NaOH solution to make mesoporous channels in the microporous crystals. Inner mesopore size could be controlled by changing the concentration of NaOH solution. The pore structure of alkaline-treated MFI zeolite was studied by instrumental analysis. To obtain the cage type mesopores, Ti-coating on the outside MFI crystals before alkaline treatment was investigated to be the most effective. Co(III) salen complexes monomers were successfully encapsulated in mesoporous MFI-type zeolite by “ship-in-a-bottle” method. The heterogeneous catalyst could be applied in asymmetric ring opening of terminal epoxides by phenol derivatives. It showed very high enantioselectivity with yield in the catalysis.

Formation of Enantiopure 5-Substituted Oxazolidinones through Enzyme-Catalysed Kinetic Resolution of Epoxides

Halohydrin dehalogenase from Agrobacterium radiobacter catalyzed the enantioselective ring opening of terminal epoxides with cyanate as a nucleophile, yielding 5-substituted oxazolidinones in high yields and with high enantiopurity (69-98% ee). This is the first example of the biocatalytic conversion of a range of epoxides to the corresponding oxazolidinones.

Carbonylative Ring Opening of Terminal Epoxides at Atmospheric Pressure

The carbonylative opening of terminal epoxides under mild conditions has been developed using Co2(CO)8 as the catalyst. Under 1 atm of carbon monoxide and at room temperature in methanol, propylene oxide is converted to methyl 3-hydroxybutanoate in up to 89% yield. This transformation is general for many terminal epoxides bearing alkyl, alkenyl, aryl, alkoxy, chloromethyl, phthalimido, and acetal functional groups. The opening takes place without epimerization at the secondary stereocenter.

Chiral (Salen) Complexes Encapsulated in Mesoporous ZSM-5 as an Optical Active Catalyst for Asymmetric Phenolic Ring Opening of Terminal Epoxides

ZSM-5 was modified by alkaline and acidic solution to introduce mesoporosity in the crystals. Heterogenized Co(III) salen was prepared in the mesopores of ZSM-5 by ‘ship-in-a-bottle’ method. Phenolic ring opening of epoxides was performed successfully by using encapsulated chiral salen catalysts. Very high enantioselectivity and conversion were obtained in PKR reaction by immobilized catalysts.

A Highly Regio‐ and Chemoselective Synthesis of Vicinal Bromohydrins by Ring Opening of Terminal Epoxides with Dibromoborane—Dimethyl Sulfide.

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Asymmetric ring-opening of epoxides on chiral Co(Salen) catalyst synthesized in SBA-16 through the “ship in a bottle” strategy

Chiral Co(Salen) complex was synthesized in the mesoporous cage of SBA-16 through the “ship in a bottle” method. The pore entrance size of SBA-16 was precisely tailored by varying the autoclaving time and silylation with phenyltrimethoxysilane to trap Co(Salen) complex in the cage of SBA-16. Chiral Co(Salen) trapped in SBA-16 shows enantioselectivity (up to 87–96% ee) as high as that of the homogeneous catalyst for the asymmetric ring opening of terminal epoxides and can be recycled at least 10 times with no apparent loss of activity. The activity for the catalyst trapped inside SBA-16 can be significantly increased when the surface is modified with organic groups. This work extends the “ship in a bottle” synthesis from microporous materials to mesoporous cage-like materials and develops an effective strategy to trap metal complex catalyst with large molecular size into the nanopores or cavities of mesoporous materials.

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.

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.