Regio- and stereoselective synthesis of aziridino epoxides from cyclic dienes

Two different routes for the regio- and stereoselective synthesis of aziridino epoxides from cyclic dienes have been explored. The first strategy involves regiospecific aziridination of cyclic diene derivatives and subsequent epoxidation with m-CPBA to yield cis-aziridino epoxides as major products. The second strategy utilizes regiospecific epoxidation of cyclic diene derivatives followed by Sharpless aziridination to provide exclusively trans-aziridino epoxides. Synthesis of both enantiomers of cis-aziridino epoxides from (R)-(-)- and (S)-(+)-carvones are also reported.     

Novel catalytic kinetic resolution of racemic epoxides to allylic alcohols

[formula: see text] The kinetic resolution of racemic epoxides via catalytic enantioselective rearrangement to allylic alcohols was investigated. Using the Li-salt of (1S,3R,4R)-3-(pyrrolidinyl)methyl-2-azabicyclo [2.2.1] heptane 1 as catalyst allowed both epoxides and allylic alcohols to be obtained in an enantioenriched form.     

Nucleophilic fluoroalkylation of epoxides with fluorinated sulfones

The unprecedented nucleophilic fluoroalkylation of simple epoxides with fluorinated sulfones was achieved to give the beta-fluoroalkyl alcohols in one step. The negative "fluorine effect" in the nucleophilic fluoroalkylation of epoxides with fluorinated carbanions was probed by the reactivity comparison between carbanions PhSO2CF2- (3) and PhSO2CCl2- (4) and between carbanions PhSO2CHF- (7) and PhSO2CHCl- (13). The mediation of this fluorine effect by introducing another electron-withdrawing benzenesulfonyl group was found to be an effective way to significantly increase the nucleophilicity of the fluorinated carbanions, with the reactivity order [(PhSO2)2CF-] (16) > PhSO2CFH- (7) > PhSO2CF2- (3).     

Heterogeneous reactions of epoxides in acidic media

Epoxides have recently been identified as important intermediates in the gas phase oxidation of hydrocarbons, and their hydrolysis products have been observed in ambient aerosols. To evaluate the role of epoxides in the formation of secondary organic aerosols (SOA), the kinetics and mechanism of heterogeneous reactions of two model epoxides, isoprene oxide and α-pinene oxide, with sulfuric acid, ammonium bisulfate, and ammonium sulfate have been investigated using complementary experimental techniques. Kinetic experiments using a fast flow reactor coupled to an ion drift-chemical ionization mass spectrometer (ID-CIMS) show a fast irreversible loss of the epoxides with the uptake coefficients (γ) of (1.7 ± 0.1) × 10(-2) and (4.6 ± 0.3) × 10(-2) for isoprene oxide and α-pinene oxide, respectively, for 90 wt % H(2)SO(4) and at room temperature. Experiments using attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) reveal that diols are the major products in ammonium bisulfate and dilute H(2)SO(4) (<25 wt %) solutions for both epoxides. In concentrated H(2)SO(4) (>65 wt %), acetals are formed from isoprene oxide, whereas organosulfates are produced from α-pinene oxide. The reaction of the epoxides with ammonium sulfate is slow and no products are observed. The epoxide reactions using bulk samples and Nuclear Magnetic Resonance (NMR) spectroscopy reveal the presence of diols as the major products for isoprene oxide, accompanied by aldehyde formation. For α-pinene oxide, organosulfate formation is observed with a yield increasing with the acidity. Large yields of organosulfates in all NMR experiments with α-pinene oxide are attributed to the kinetic isotope effect (KIE) from the use of deuterated sulfuric acid and water. Our results suggest that acid-catalyzed hydrolysis of epoxides results in the formation of a wide range of products, and some of the products have low volatility and contribute to SOA growth under ambient conditions prevailing in the urban atmosphere.     

Substituted epoxides by lithiation of terminal epoxides

Diamine-ligand-assisted direct hydrogen-lithium exchange allows the generation of nonstabilized (H-substituted) oxiranyllithium species and their subsequent trapping by Bu(3)SnCl and carbonyl-based electrophiles. This reaction provides a new concise route to alpha,beta-epoxystannanes and substituted epoxides.     

Reaction of some trisubstituted steroid epoxides with triphenylphosphine - iodine complex. Deoxygenation of epoxides

Triphenylphosphine - iodine complex was found to be an effective reagent for deoxygenation of trisubstituted steroidal epoxides. The mechanism of the reaction is proposed.     

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.     

生物催化合成光学活性环氧化物

手性环氧化物及其相应的邻二醇在合成上具有重要应用价值。近年来,制取这些手性合成块的合成方法得到了很的大发展。本文着重讨论当前国际上采用生物催化合成光学活性环氧化物的发展状况。     

Ruthenium-catalyzed cyclization of alkyne-epoxide functionalities through alternation of the substituent and structural skeleton of epoxides

Treatment of 1-(o-ethynylphenyl)-2-alkyl-2-aryl epoxides with TpRuPPh(3)(CH(3)CN)(2)PF(6) catalyst (10 mol %) in hot toluene (100 degrees C, 12 h) led to an atypical cyclization and gave 1-aryl-2-alkyl-1H-indene derivatives and carbon monoxide efficiently. The cyclization of 1-cis-enynyl-2-alkyl epoxides with this catalyst in hot toluene (10 mol %, 100 degrees C, 12 h) gave 2,5-disubstituted phenols in 45-72% yields. Under the same conditions, 1-cis-enynyl- 2,2-dialkyl epoxides and 1-cis-enynyl- 2-alkyl-2-aryl epoxides gave the corresponding 6,6-disubstituted cyclohexa-2,4-dien-1-ones in good yields (85-91%). Mechanisms for these new cyclization reactions are proposed on the basis of trapping experiments and isotope labeling experiments. The formation of 1H-indene products likely involves ruthenium-acyl intermediates whereas cyclohexa-2,4-dien-1-ones are thought to derive from ruthenium-ketene intermediates.     

Deprotonation-electrophile trapping of terminal epoxides

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.     

Regio-controlled ring-opening polymerization of perfluoroalkyl-substituted epoxides

Highly fluorinated epoxides were polymerized under mild conditions regioregularly, which gave easy access to isotactic polymers by using optically pure epoxides.     

Unusual reactivity of selenoboranes towards epoxides: new selective routes to b-hydroxyselenides and allylalcohols

Selenoboranes react with terminal α,β- di- and trisubstituted epoxides to produce β-hydroxylenides, (or olefins) in the two first cases and allyl alcohols in the last one. A very high stereodescrimination has been observed for α,β-disubstituted epoxides: the cis epoxide being much more reactive.     

Carbon-13 NMR spectra of some epoxides derived from dicyclopentadiene

The ¹³C NMR spectra of a series of epoxides derived from endo- and exo-dicyclopentadiene and their partially hydrogenated compounds were determined to examine the substituent effects arising from the introduction of the oxirane ring in comparison with those found in other ring systems. The ¹³C signals of some epoxides were assigned by using lanthanide shift reagents. Characteristic substituent effects exerted by an oxirane ring were demonstrated. Marked steric γ-effects of ?8—13 ppm were observed at the bridge carbon signal in the bicyclo[2.2.1]heptane skeleton. Differences were found in the substituent effects between endo- and exo-dicyclopentadiene epoxides, and have been discussed in relation to the molecular geometry.     

The photochemical preparation of ozonides by electron-transfer photo-oxygenation of epoxides

9,10-Dicyanoanthracene (DCA) sensitizes the electron-transfer photo-oxygenation of epoxides in oxygen-saturated acetonitrile to form ozonides. Epoxides with oxidation potentials lower than 2 V vs SCE quench the fluorescence of DCA and are converted to the ozonides with DCA alone. Epoxides which do not quench the singlet excited state of DCA are unreactive under these conditions. However, the photo-oxygenation of these epoxides can be effected by addition of biphenyl (BP) as a catalyst or co-sensitizer. Investigations of the stereochemistry of the reactions of cis- and trans-2,3-diaryloxiranes has shown that both isomeric epoxides are converted exclusively to the corresponding cis-ozonides. Co-sensitized photo-oxygenation of cis- and trans-2,3-diphenyloxirane affords only cis-3,5-diphenyl-1,2,4-trioxolane. The same stereochemical course is followed for the electron-transfer photo-oxygenation of more easily oxidized 2,3-dinaphthyloxiranes that do not require BP co-sensitization. The stereochemistry of the naphthyl-substituted ozonides has been unequivocably assigned by an X-ray structure of cis-3,5-bis(2'-naphthyl)-1,2,4-trioxolane. The corresponding trans-ozonide was prepared by ozonation of cis-1,2-bis(2'-naphthyl)ethene and stereochemically identified by Chromatographic resolution using high-performance liquid chromatography with optically active (+)-poly(triphenylmethyl methacrylate) as the stationary phase. These stereochemical results have been interpreted in terms of a mechanism involving addition of singlet oxygen as a dipolarophile to intermediate carbonyl ylides.     

Azacycloalkanes from epoxides and aziridines

Methods of preparation of azetidines, pyrrolidines, and piperidines from epoxides and aziridines were analyzed. The possibility of epoxides conversion into aziridines was considered. The examples of application of azacycloalkanes in the medical and organic chemistry as biologically active substances and synthons for their preparation were calculated.     

Studies in the chemistry of chromone epoxides

Chromones and isoflavones, but not flavones, were epoxidized by alkaline hydrogen peroxide. 3-Substituted chromone epoxides were considerably more stable than others; one isoflavone epoxide was converted into a fluorohydrin, another into a 1,2-diol. The latter is a 2-hydroxychromanone and a similarly structured compound was obtained by the cyclisation of 2'-benzoyloxy-2,2-dibromoacetophenone. Acid-catalysed ring-opening of chromone epoxides occurred regioselectively yielding 3-hydroxychromanones. Base-catalysed ring-opening also occurred regioselectively but at the 3-position. Acid- and base-catalysed hydrolysis of 2-methy-lisoflavone epoxide resulted in cleavage of both heterocyclic rings, yielding, respectively, a 1,3- and a 1,2-diketone. This epoxide formed a cyclic sulphate with sulphuric acid.     

Acid-catalyzed rearrangement of aryl-substituted homobenzoquinone epoxides

The BF3-catalyzed reactions of diphenyl-substituted and endo-monophenyl-substituted homobenzoquinone epoxides proceeded through a regioselective oxirane ring opening followed by participation of a pi-aryl transannular cyclization to give the tricyclic diketo alcohols. The conformationally semirigid ethano-bridged diphenyl-substituted homologues also provided similar diketo alcohols and the subsequent ring-expanded cycloheptenedione (via a subsequent 1,2-acyl migration associated with cyclopropane ring opening), depending on the methyl-substitution pattern of the quinone frame. However, the exo-monophenyl-substituted and the rigid biphenyl-2,2'-diyl-substituted homobenzoquinone epoxides essentially remained unchanged.     

Liquid crystalline epoxides with long lateral substituents: Synthesis and curing

A series of liquid crystalline epoxides with long lateral substituent from 4 to 12 carbon atoms was synthesized and characterized by ¹H NMR, FTIR spectroscopy, differential scanning calorimetry (DSC), polarized light optical microscopy (POM). The curing products of the LCE with DDM, was analyzed by POM and WAXS. The cure kinetics of epoxides and aromatic amine was investigated. The curing activation energy about 43.3-53.2 kJ mol⁻¹ was determined and compared for all the LC epoxides through Ozawa method. The change of activation energy suggests that the reaction active depends upon the lateral substituents, because the lateral substituents parallel to the rod-like core and can act as bound solvent.     

A convenient resolution of long-chain alkyl epoxides with Jacobsen's salen(Co)III(OAc) catalysts

Non-racemic terminal long-chain alkyl epoxides are prepared from racemic epoxides and 1 mol% (R,R)- and (S,S)-salen(Co)III catalysts following a modified procedure for kinetic resolution. The ee's for all epoxides (C-10, C-12, C-14, C-16, C-18, C-20) exceed 95% and the chemical yields range from 85% to 95%.     

Conversion of epoxides to 1,3-dioxolanes catalyzed by tin(II) chloride

Anhydrous tin(II) chloride is an efficient catalyst for the reaction of epoxides with acetone to prepare 2,2-dimethyl-1,3-dioxolanes (acetonides) in good to excellent yields. Mono-, di-, and trisubstituted epoxides participate equally well in this diastereospecific reaction. The use of single enantiomer epoxides under the reported conditions results in significant erosion of optical activity.