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1.
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. 相似文献
2.
A new and efficient process for the conversion of terminal epoxides to gamma-butanolides is described involving Lewis acid promoted epoxide ring-opening by 1-morpholino-2-trimethylsilyl acetylene. Addition of a terminal epoxide to a solution of the ynamine and boron trifluoride diethyl etherate in dichloromethane at 0 degrees C rapidly affords a cyclic keteneaminal that can be hydrolyzed and protodesilylated under mild conditions to provide the corresponding gamma-butanolide in high yield. The net transformation is equivalent to an acetate enolate opening of terminal epoxides. The formation of a cyclic keteneaminal as the direct addition product was observed by monitoring of the reaction by IR and NMR spectroscopy. Functionalized gamma-lactones were prepared by the interception of the reactive cyclic keteneaminal prior to hydrolysis. Reactions with enantiomerically enriched terminal epoxides provide the corresponding gamma-butanolides without loss of optical activity. The compatibility of the present methodology with a wide range of functional groups is noteworthy. 相似文献
3.
Formation of enantiopure 5-substituted oxazolidinones through enzyme-catalysed kinetic resolution of epoxides 总被引:1,自引:0,他引:1
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. 相似文献
4.
Santosh Singh Thakur Wenji Li Seong-Jin Kim Geon-Joong Kim 《Journal of organometallic chemistry》2006,691(9):1862-1872
A new dinuclear chiral Co(salen) complexes bearing group 13 metals have been synthesized and characterized. The easily prepared complexes exhibited very high catalytic reactivity and enantioselectivity for the asymmetric ring opening of epoxides with H2O, chloride ions and carboxylic acids and consequently provide enantiomerically enriched terminal epoxides (>99% ee). It also catalyzes the asymmetric cyclization of ring opened product, to prepare optically pure terminal epoxides in one step. The homogeneous dinuclear chiral Co(salen) have been covalently immobilized on MCM-41. The potential benefits of heterogenization include facilitation of catalyst separation and recyclability requiring very simple techniques. The system described is very efficient. 相似文献
5.
The binuclear chiral (salen) Co complexes bearing Lewis acids of Al and Ga catalyze regio- and enantioselective ring opening of terminal epoxides with carboxylic acids. The ring opened product of epichlorohydrin with carboxylic acids followed by cyclization step in the presence of catalyst and base represent straightforward, efficient methods for the synthesis of enatiomerically enriched (>99% ee) valuable terminal epoxides. Strong synergistic effects of different Lewis acid of Co-Al and Co-Ga were exhibited in the catalytic process. 相似文献
6.
The enormous growth in the use of polymer resin supports in solid phase combinatorial synthesis, and related methodologies, has re-stimulated interest in the area of polymer-supported transition metal complex catalyst .The recently developed chiral salen-based for the enantioselective ring opening of meso epoxides and kinetic resolution of terminal epoxides are appealing candidates for immobilization on solid support. The catalysts are reading prepare from inexpensive components, and are amenable to modification for attachment to a solid support. 相似文献
7.
I. Victor Paul Raj 《Tetrahedron letters》2008,49(16):2646-2648
A concise route to the asymmetric synthesis of (S)-vigabatrin® and (S)-dihydrokavain has been described using Co-catalyzed hydrolytic kinetic resolution of racemic epoxides and regiospecific opening of terminal epoxides with dimethylsulfonium methylide as the key steps. 相似文献
8.
《Arabian Journal of Chemistry》2020,13(11):8200-8208
β-Hydroxynitriles are essential intermediates in the synthesis of diverse bioactive compounds and clinical drugs. One of the precursor reactions to these intermediates is the opening of an epoxide ring with a cyanide nucleophile. In the present study, we report a milder and safer route to β-hydroxynitriles employing recyclable, Amberlyst A-21 resin in the ring-opening of epoxides with acetone cyanohydrin in water. A diverse range of substrates (fifteen), including aromatic epoxides, phenoxy epoxides, non-terminal, and terminal aliphatic epoxides, are investigated under the optimized conditions to afford the desired β-hydroxynitriles in good to excellent yield. In addition to this, the recyclability of the Amberlyst A-21 resin is also successfully demonstrated. This relatively safer methodology has the potential to be explored in other organic transformations. 相似文献
9.
Montmorillonite K 10 efficiently catalyses the opening of epoxide rings by amines in high yields with excellent regio- and diastereo-selectivities under solvent-free conditions at room temperature affording an improved process for synthesis of 2-amino alcohols. Reaction of cyclohexene oxide with aryl/alkyl amines leads to the formation of trans-2-aryl/alkylaminocyclohexanols. For unsymmetrical epoxides, the regioselectivity is controlled by the electronic and steric factors associated with the epoxide and the amine. Selective nucleophilic attack at the benzylic carbon of styrene oxide takes place with aromatic amines, whereas, aliphatic amines exhibit preferential nucleophilic attack at the terminal carbon. Aniline reacts selectively at the less hindered carbon of other unsymmetrical epoxides. The difference in the internal strain energy of the epoxide ring in cycloalkene oxides and alkene oxides led to selective nucleophilic opening of cyclohexene oxide by aniline in the presence of styrene oxide. Due to the chelation effect, selective activation of the epoxide ring in 3-phenoxy propylene oxide takes place in the presence of styrene oxide leading to preferential cleavage of the epoxide ring in 3-phenoxy propylene oxide by aniline. 相似文献
10.
Lithiation-in situ silylation of terminal epoxides using lithium 2,2,6,6-tetramethylpiperidide in combination with phenyldimethyl(or diethyl)silyl chloride provides a direct process for the synthesis of trans-α,β-epoxysilanes, which undergo α-ring opening with alkenylcoppers to give syn-β-hydroxyallylic silanes. The chemistry is applied in an annulation approach to the C(10)-C(19) tetrahydrofuran-containing portion of the lytophilippines. 相似文献
11.
Dr. José A. Castro‐Osma Prof. Michael North Dr. Xiao Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(6):2100-2107
Chromium and aluminium salphen complexes have been found to display remarkable catalytic activity in the synthesis of cyclic carbonates from a range of epoxides and carbon dioxide. The Al(salphen) complex is more reactive towards terminal epoxides at ambient temperature and pressure, whereas the Cr(salphen) complex exhibits higher catalytic activity towards more challenging internal epoxides at elevated temperature and pressure. 相似文献
12.
13.
In the presence of BF3, a series of symmetrical and unsymmetrical ethers reacted with epichlorohydrin and 2‐[(benzyloxy)methyl]oxirane, two terminal epoxides, to afford 1‐alkoxy‐3‐chloropropan‐2‐ol and 1‐alkoxy‐3‐(benzyloxy)propan‐2‐ol. The cleavage of unsymmetrical ethers occurred via an SN2 or SN1 mechanism. Secondary epoxides did not give similar ring‐opening products. 相似文献
14.
Additions of terminal alkynes to electrophiles are important transformations in organic chemistry. Generally, activated terminal alkynes react with epoxides in an S(N)2 fashion to form homopropargylic alcohols. We have developed a new synthetic method to form propargylic alcohols from epoxides and terminal alkynes via 1,2-shifts. This method involves cationic zirconium acetylides as both the activator of epoxides and nucleophiles. Due to the mild conditions to pre-activate alkynes with silver nitrate, this synthetic method is useful for both electron-rich and electron-deficient alkynes with other acid- and base-sensitive functional groups. 相似文献
15.
The suppression of α-elimination during opening of epoxides by lithium amides (RRNLi) is possible by the use of HMPT as a solvent. This solvent effect is general and is of some interest for the preparation of allylic alcohols by epoxides opening with lithium amides. Formation of by-products such as ketones or aminoalcohols is also avoided in this polar solvent. 相似文献
16.
Shahram Tangestaninejad Majid Moghadam Valiollah Mirkhani Bahram Yadollahi S. Mohammad R. Mirmohammadi 《Monatshefte für Chemie / Chemical Monthly》2006,137(2):235-242
Summary. Efficient ring opening of epoxides under mild conditions is reported. Potassium dodecatungstocobaltate(III) trihydrate was
used as an efficient catalyst for the alcoholysis and acetolysis of epoxides. Conversion of epoxides to thiiranes was also
performed efficiently in the presence of this catalyst. 相似文献
17.
Hodgson DM Kirton EH Miles SM Norsikian SL Reynolds NJ Coote SJ 《Organic & biomolecular chemistry》2005,3(10):1893-1904
Organolithium-induced deprotonation of terminal epoxides in the presence of appropriate diamine ligands allows trapping with a range of electrophiles, yielding functionalised di- and tri-substituted epoxides in good yields and with control of stereochemistry at the epoxide. 相似文献
18.
BHBr2-DMS and BH2Br-DMS have been found to be highly promising, mild, stereo- and regioselective reagents useful in the opening of epoxides to the corresponding halohydrins at 0 °C to ambient temperature. Except for styrene oxide, all the terminal epoxides were regioselectively cleaved by borderline SN2-type mechanisms favoring the formation of primary vs secondary bromides. In contrast to B-bromobis(dimethylamino)borane (BDB), the polarity of the solvent has very little or no effect on the regioselectivity achieved by BH2Cl-DMS and BH2Br-DMS. In addition, the regioselectivities were not greatly affected by variation of temperature in the case of BH2Cl-DMS and BH2Br-DMS. BH2Br-DMS and BHBr2-DMS are very useful hydroborating agents with their own regio- and chemospecific reactivity. BH2Br-DMS cleaves epoxides chemo- and regioselectively in the presence of reactive functional groups such as olefin and phenylalkyl ether, especially cleanly at lower temperatures. 相似文献
19.
The scope of reductive decyanation and spiroannulation reactions has been expanded to include secondary electrophiles for potentially useful transformations. Secondary phosphates and chlorides, as well as terminal epoxides, cyclize in a stereospecific fashion. Both endo and exo modes of cyclization were observed with terminal epoxides. 相似文献
20.
Fernando Castro‐Gómez Giovanni Salassa Prof. Dr. Arjan W. Kleij Prof. Dr. Carles Bo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(20):6289-6298
The reaction mechanism for the Zn(salphen)/NBu4X (X=Br, I) mediated cycloaddition of CO2 to a series of epoxides, affording five‐membered cyclic carbonate products has been investigated in detail by using DFT methods. The ring‐opening step of the process was examined and the preference for opening at the methylene (Cβ) or methine carbon (Cα) was established. Furthermore, calculations were performed to clarify the reasons for the lethargic behavior of internal epoxides in the presence of the binary catalyst. Also, the CO2 insertion and the ring‐closing steps have been explored for six differently substituted epoxides and proved to be significantly more challenging compared with the ring‐opening step. The computational findings should allow the design and application of more efficient catalysts for organic carbonate formation. 相似文献