A comparative study of the epoxidation of homoisoflavones (3‐benzyl‐4‐chromones) 1–4 has been performed by various oxidizing agents, víz. Epoxidation with isolated dimethyldioxirane (Method A), with alkaline hydrogen peroxide (Method B), and with sodium hypochlorite (Method C) to obtain the epoxides 4–8 . Compounds 2 and 3 have also been oxidized with a combination of dimethyldioxirane and Jacobsen's Mn(III)salen catalysts (R,R)‐11 and (S,S)‐ 11 to afford 3‐benzoyl‐4‐chromones 9 and 10 . Structures of all new compounds have been elucidated by microanalyses, ir and nmr spectroscopic measurements. 相似文献
Corey‐Chaykovsky epoxidation has been widely applied in the conversion of aldehydes and ketones to epoxides with sulfonium and sulfoxonium ylides. The reverse transformation is realized for conversion of geminal disubstituted epoxides to ketones in the presence of DABCO in refluxing mesitylene. The method is a weak basic transformation from epoxides to ketones with loss of a methylene group and can be applied as an alternative strategy of the acid‐catalyzed Meinwald rearrangement or oxidation for conversion of epoxides to carbonyl compounds. 相似文献
Mononuclear nonheme high‐spin (S=2) iron(IV)–oxo species have been identified as the key intermediates responsible for the C?H bond activation of organic substrates in nonheme iron enzymatic reactions. Herein we report that the C?H bond activation of hydrocarbons by a synthetic mononuclear nonheme high‐spin (S=2) iron(IV)–oxo complex occurs through an oxygen non‐rebound mechanism, as previously demonstrated in the C?H bond activation by nonheme intermediate (S=1) iron(IV)–oxo complexes. We also report that C?H bond activation is preferred over C=C epoxidation in the oxidation of cyclohexene by the nonheme high‐spin (HS) and intermediate‐spin (IS) iron(IV)–oxo complexes, whereas the C=C double bond epoxidation becomes a preferred pathway in the oxidation of deuterated cyclohexene by the nonheme HS and IS iron(IV)–oxo complexes. In the epoxidation of styrene derivatives, the HS and IS iron(IV) oxo complexes are found to have similar electrophilic characters. 相似文献
Regioselective epoxidation of 3‐aryl‐1‐(3‐coumarinyl)propen‐1‐ones 1–10 by isolated dimethyldioxirane afforded the appropriate epoxides 11–20 in high (76–87%) yields. 相似文献
Regioselective epoxidation of 3‐(3‐oxo‐3‐arylpropenyl)chromen‐4‐ones 1a‐h by isolated dimethyldioxirane provided epoxides 2a‐h as sole detectable and isolable products in good (75–86%) yields. 相似文献
A series of 12 new 2‐(3, 5‐dimethoxy‐4‐((1‐Aryl‐4H‐1, 2, 3‐triazol‐4‐yl) methoxy) phenyl) benzo[d]thiazoles have been synthesized from the reaction of 4‐hydroxy‐3, 5‐dimethoxybenzaldehyde, o‐amino thiophenol, propargyl bromide, and different substituted aromatic azides using “click chemistry”. The structures of these compounds were established on the basis of Fourier Transform infrared, 1H NMR, 13C–NMR, and mass spectral analysis. Compounds ( 6a–l ) were screened for in vitro antimicrobial activity. 相似文献
A simple and rapid HPLC method using a polysaccharide‐based chiral stationary phase (Chiralpak AD‐H) in polar‐organic phase mode has been developed for direct resolution of glycidyl nitrobenzoate (GNB) and 2‐methyl glycidyl nitrobenzoate (MGNB) enantiomers. ACN and methanol were used as mobile phase and the effects of the addition of ethanol and 2‐propanol as organic modifier in the mobile phase, flow rate and the column temperature were tested. The optimized conditions were: methanol/ethanol (80:20) at a flow rate of 0.9 mL/min and 40°C. Analysis time was ?13 min and the chiral resolution was ?2. The method was validated and resulted to be selective, precise and accurate. The method was found to be linear in 2–300 μg/mL range (R2 >0.999) with an LOD nearly 0.5 μg/mL for four enantiomers. GNB and MGNB enantiomers were obtained by asymmetric epoxidation of allyl alcohol and 2‐methyl allyl alcohol, respectively, using chiral titanium–tartrate complexes as catalyst and dichloromethane as solvent after in situ derivatization of the intermediate glycidols derivatives. The quite simple and rapid validated method was applied successfully for direct determination of the enantiomeric excess (?90%) and yield obtained in real samples of asymmetric epoxidation of allylic alcohols without further purification, workup or solvent removal. The method provides a useful and value‐added tool for controlling the enantiomeric purity of the synthesized epoxides. 相似文献
A general and highly enantioselective method for the epoxidation of cis‐alkenylsilanes, in which the epoxysilanes were obtained with complete enantioselectivity in the presence of 0.5–2 mol % of a Ti–Salalen complex. The combination of this epoxidation method and the following transformations is a powerful approach that provides synthetically important epoxides, such as styrene oxides and geminally disubstituted epoxides, in enantiopure form.
Asymmetric epoxidation of N-enoylsultams (1, 3-15) incorporating a variety of chiral sultams as the chiral induction elements with UHP/TFAA has been studied. Both diastereomeric isomers of epoxides (2, 16-28) were obtained in high yield and moderate to high optical purity. 相似文献
Reaction between an aqueous ethanol solution of tin(II) chloride and that of 4‐propanoyl‐2,4‐dihydro‐5‐methyl‐2‐phenyl‐3 H‐pyrazol‐3‐one in the presence of O2 gave the compound cis‐dichlorobis(4‐propanoyl‐2,4‐dihydro‐5‐methyl‐2‐phenyl‐3 H‐pyrazol‐3‐onato) tin(IV) [(C26H26N4O4)SnCl2]. The compound has a six‐coordinated SnIV centre in a distorted octahedral configuration with two chloro ligands in cis position. The tin atom is also at a pseudo two‐fold axis of inversion for both the ligand anions and the two cis‐chloro ligands. The orange compound crystallizes in the triclinic space group P 1 with unit cell dimensions, a = 8.741(3) Å, b = 12.325(7) Å, c = 13.922(7) Å; α = 71.59(4), β = 79.39(3), γ = 75.18(4); Z = 2 and Dx = 1.575 g cm–3. The important bond distances in the chelate ring are Sn–O [2.041 to 2.103 Å], Sn–Cl [2.347 to 2.351 Å], C–O [1.261 to 1.289 Å] and C–C [1.401 Å] the bond angles are O–Sn–O 82.6 to 87.7° and Cl–Sn–Cl 97.59°. The UV, IR, 1H NMR and 119Sn Mössbauer spectral data of the compound are reported and discussed. 相似文献
Amphidinolide N, the structure of which has been recently revised, is a 26‐membered macrolide featuring allyl epoxide and tetrahydropyran moieties with 13 chiral centers. Due to its challenging structure and extraordinary potent cytotoxicity, amphidinolide N is a highly attractive target of total synthesis. During our total synthesis studies of the 7,10‐epimer of the proposed structure of amphidinolide N, we have synthesized the C1–C13 subunit enantio‐ and diastereoselectively. Key reactions include an l ‐proline catalyzed enantioselective intramolecular aldol reaction, Evans aldol reaction, Sharpless asymmetric epoxidation and Tamao–Fleming oxidation. To aid late‐stage manipulations, we also developed the 4‐(N‐benzyloxycarbonyl‐N‐methylamino)butyryl group as a novel ester protective group for the C9 alcohol. 相似文献
In an attempt to synthesize antibacterial agents effective against gram‐positive and gram‐negative bacteria, the efficient synthesis of novel bis‐azetidinones ( 3a–j ) has been established. Thus, cycloaddition reaction of substituted bis‐imines with chloroacetylchloride under microwave irradiation in the presence of zeolite yielded bis‐azetidinones ( 3a–j ). Structures of the synthesized compounds have been elucidated on the basis of their elemental analysis and spectral data (IR, 1H‐NMR, 13C‐NMR, and mass spectra). The synthesized bis‐azetidinones were screened for their antibacterial activity against five microorganisms: Bacillus subtilis, Proteus vulgaris, Staphylococcus aureus, Klebsiella pneumoniae, and Escherichia coli. They were found to exhibit good to moderate antibacterial activity. 相似文献