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1.
Studies in Stereochemistry XIV. Diels-Alder adducts in the resin series; action of peracids and acid-catalysed ring opening of epoxides The synthesis of Diels-Alder compounds of type 2 with a 17-nor-13(14)-atisène skeleton is described (cf. Schemes 1–3). Depending on the nature and configuration of substituents R1 and R2 on the carbon atoms 15 and 16, an epoxide ( 24–33 ) or a ketone ( 35–38 ) or a mixture of epoxide, ketone and lactone is obtained by the action of p-nitroperbenzoic acid on the double bond of these adducts (cf. Scheme 4). A simplified reaction scheme is suggested to explain the formation of the various products. In an acid-catalysed reaction, the epoxides isomerize mainly into ketones. Nevertherless, in some cases, dienes (e.g. 52 ) or hydroxy-γ-lactones of (13R*, 14S*)-configuration (e.g. 50 ) resulting from the opening of the epoxide ring with retention of configuration were obtained.  相似文献   

2.
ω-Alkenoic acids, either commercially available or synthesized, were esterified to their corresponding methyl esters. They were characterized by their infrared, 1H-, and 13C-NMR spectra. The ω-alkenoates prepared were: propenoate (acrylic acid), butenoate, pentenoate, hexenoate, heptenoate, octenoate, nonenoate, and decenoate. These compounds were epoxidized with m-chloroperoxybenzoic acid to the corresponding methyl ω-epoxyalkanoates. The rate of epoxidation of the double bond is found to increase as the double bond is separated from the carbomethoxy group by increasing numbers of methylene groups. When at least three methylene groups are inserted, the rate of epoxidation becomes constant and is similar to the epoxidation of ω-olefins. The methyl ω-epoxyalkanoates were characterized by their infrared, 1H-, and 13C-NMR spectra. Methyl ω-alkenoates and methyl ω-epoxyalkanoates were prepared and characterized, and their purification was studied in preparation for their investigation as monomers for olefin or epoxide polymerization using corrdination initiators.  相似文献   

3.
The configuration of conformationally homogeneous epoxides in trans bicyclo-(n.3.0) alkanes is established by progressive complexation with Eu(dpm)3. The examples described demonstrate the importance of this method which is superior to all the other physicochemical methods already used to determine the cyclopentane epoxide configuration.  相似文献   

4.
Carbohydrate Derivatives Bearing a gem-Dihalogenoethenyl Group Treated with the appropriate Wittig reagent, aldehydosugar derivatives ( 1–13 ) led in good to excellent yields to the expected gem-difluoro, gem-chlorofluoro-and/or gem-dichloroenoses ( 14–29 ). Examples of their dibromo analogues had been previously described (see e.g. [1]) but the diiodo derivatives could not be isolated, The influence of the conditions on the yields is reported as well as spectroscopic properties (particularly the long-range 13C, 19F- and 1H, 19F-coupling constants) of these new enoses.  相似文献   

5.
Lipophilic Tetraazamacrocyles: Extraction of Metal Ions by Impregnated Resin Extraction of Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Pb2+ and Ag+ by lipophilic tetraazamacrocycles dispersed on a solid matrix (Amberlite XAD7) is reported. Extraction efficiency is sensitive to the metal ion identity and the cavity size of the macrocycle. The influence of kinetic factors upon extraction efficiency is discussed.  相似文献   

6.
The addition reaction of 2,2‐bis‐[4‐(2,3‐epoxypropoxy)‐phenyl]‐propane (DGEBA) and preformed complexes of metal ions and disecondary diamines led to a large quantity of cyclic epoxide–amine oligomers. As shown by gel permeation chromatographic analysis, cycles of n = 1, 2, and 3 were formed. Functional epoxide end groups of the prepared oligomers were completely missing in the IR and 1H NMR and 13C NMR spectra. In the fast atom bombardment and matrix‐assisted laser desorption/ionization mass spectra, the molecular ions of the n = 1, 2, 3 cycles of DGEBA and N,N′‐dibenzyl‐5‐oxanonanediamine‐1,9 were detected at m/z = 680, 1361, and 2042. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2047–2052, 2003  相似文献   

7.
The peri effect induced by the phenyl group has been studied in the anthracene series by means of 1H and 13C n.m.r. The chemical shifts of overcrowded protons can be explained by a combination of magnetic anisotropy and steric effects. Steric contributions amount to c. 25% of the phenyl induced shift at the peri position. Amongst published ring-current theories, only the model of Johnson and Bovey is capable of describing correctly the shielding region of the phenyl group. The unexpected shieldings and deshieldings, observed by 13C n.m.r. in the case of very hindered derivatives, is probably due to distortions of the anthracene skeleton.  相似文献   

8.
Benzoyl-CoA epoxidase is a dinuclear iron enzyme that catalyzes the epoxidation reaction of the aromatic ring of benzoyl-CoA with chemo-, regio- and stereo-selectivity. It has been suggested that this enzyme may also catalyze the deoxygenation reaction of epoxide, suggesting a unique bifunctionality among the diiron enzymes. We report a density functional theory study of this enzyme aimed at elucidating its mechanism and the various selectivities. The epoxidation is suggested to start with the binding of the O2 molecule to the diferrous center to generate a diferric peroxide complex, followed by concerted O–O bond cleavage and epoxide formation. Two different pathways have been located, leading to (2S,3R)-epoxy and (2R,3S)-epoxy products, with barriers of 17.6 and 20.4 kcal mol–1, respectively. The barrier difference is 2.8 kcal mol–1, corresponding to a diastereomeric excess of about 99 : 1. Further isomerization from epoxide to phenol is found to have quite a high barrier, which cannot compete with the product release step. After product release into solution, fast epoxide–oxepin isomerization and racemization can take place easily, leading to a racemic mixture of (2S,3R) and (2R,3S) products. The deoxygenation of epoxide to regenerate benzoyl-CoA by a diferrous form of the enzyme proceeds via a stepwise mechanism. The C2–O bond cleavage happens first, coupled with one electron transfer from one iron center to the substrate, to form a radical intermediate, which is followed by the second C3–O bond cleavage. The first step is rate-limiting with a barrier of only 10.8 kcal mol–1. Further experimental studies are encouraged to verify our results.  相似文献   

9.
The photochemical behavior of various substituted epoxycarbonyl compounds consisting of more than one possible photo‐labile site (i.e. δ‐hydrogen, β‐hydrogen and epoxide ring) has been investigated. These compounds on photo‐irradiation produced the β‐hydroxyenones in an eco‐friendly green approach. Mechanistically, these photo‐transformations have been envisaged to occur via an intramolecular β‐hydrogen abstraction by the carbonyl group of benzoyl moiety to generate the 1,3‐biradical followed by epoxide ring opening that isomerizes into the photoproducts. The photolysis of the probed epoxy ketones didn’t furnish any photoproduct through δ‐hydrogen abstraction, whatsoever. This exclusive preference for β‐H abstraction over δ‐H abstraction by carbonyl group has been vindicated by the MM2 energy mini‐ mized program for the investigated photochemical substrates. The structures of these photoproducts were established from the analysis of their spectral parameters (IR, 1H/13C NMR and Mass) and single crystal X‐ray crystallography data.  相似文献   

10.
Twenty-six monoalkoxyfluorophosphoranes bearing an asymmetric substituent of types R1PF3(OR2*)( 1 ), R1*PF3(OR2) ( 2 ), R1R3PF2(OR2* 3 ) and R21PF2(OR2*)( 4 ), have been prepared. The non-equivalence of the axial fluorine atoms is observed in the 19F NMR spectra for the compounds of types 1 δF′a – δF′a ~ 0·5 to 3·8 ppm, J(FaF′a) ~ 10 Hz, 2 δFa – δF′a ~ 1·1 to 1·5 ppm, J(FaF′a) ~ 14 Hz and 3 δFa – δFa ~ 0·2 ppm, J(FaF′a) ~ 10 Hz but not for those of type 4 R12PF2(OR2*). Its origin is assigned to the diastereotopic character of these fluorines. The possibility of a hindered rotation of the substituents as the origin of the phenomenon is excluded. The preparation of sec-BuPF4 and EtPhPF3 is also reported.  相似文献   

11.
14N-NMR. measurements using the Fourier Transform technique are presented and compared to C. W. experiments. The F. T. technique is especially advantageous for relaxation time measurements. However, since 14N-nuclei may have widely different relaxation times, it is often not possible to have optimal gain in sensitivity (as compared to C. W. measurements) in a single F. T. experiment for different 14N-nuclei contained in the same sample. Different experiments have to be performed, optimizing the spectrometer parameters for each 14N-resonance of appreciably different linewidth. The technique is applied to three different problems. 14N-relaxation in symmetrical ammonium salts is shown to arise from reorientation of the water dipoles. The use of a double spin-probe, 13C-14N, allows the determination of the electric field gradients in cyclic ammonium salts. The electronic distribution is especially distorted from tetrahedral symmetry in the highly strained N, N-dimethyl-aziridinium cation. Finally, electric and dynamic effects in ion pairing may be studied as shown on the case of tetrabutylammonium iodide in water and in benzene.  相似文献   

12.
17O-NMR. Aliphatic aldehydes and ketones, additivity of substituent effects and correlation with 13C-NMR. The 17O-chemical shifts of 9 aldehydes, 22 aliphatic and 4 alicyclic ketones, in the natural abundance FT.-NMR. spectra followed a good correlation with the 13C-chemical shifts of the terminal C-atoms of corresponding methylene compounds. An additivity relation involving 6 parameters represents the 17O-shifts of 28 of the measured products with a standard deviation of 2.5 ppm. The additivity parameters are discussed with respect to the modifications of the polarity of the carbonyl group induced by the hyperconjugative interaction of π and π* orbitals with the πCH 3 orbitals of the alkyl substituent groups.  相似文献   

13.
Hybrid organic–inorganic materials derived from 3‐glycidoxypropyltrimethoxylsilane were prepared via two different synthetic routes: (1) the HCl‐catalyzed sol–gel approach of silane followed by the lithium perchlorate (LiClO4)/HCl‐catalyzed opening of epoxide and (2) the simultaneous gelation of tin/LiClO4‐catalyzed silane/epoxide groups. LiClO4 catalyzed the epoxide polymerization, and its effects on the structures of these hybrid materials were studied by NMR. The structure of the inorganic side was probed by solid‐state 29Si NMR spectroscopy, and the characterizations of the organic side and the chemical processes involved in the different synthetic routes were performed with solid‐state cross‐polarity/magic‐angle‐spinning 13C NMR. The different synthetic routes significantly affected the polymerization behaviors of the organic and inorganic sides in the presence of LiClO4. A larger amount of LiClO4 promoted the opening of epoxide and led to the formation of longer poly(ethylene oxide) chains via the HCl‐catalyzed sol–gel approach, whereas in the case of the tin‐catalyzed approach, the faster polymerization of the inorganic side hindered the growth of the organic network. The addition of LiClO4 was proven to be without crystalline salt present in the hybrid networks by wide‐angle X‐ray powder diffraction. Also, the interactions between the ions and hybrid host, examined with Fourier transform infrared and 7Li proton‐decoupled magic‐angle‐spinning NMR, further demonstrated that extensive ion aggregation existed in these hybrid materials. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 151–161, 2004  相似文献   

14.
The Cope rearrangement of 2,3-divinyloxiranes, a rare example of epoxide C–C bond cleavage, results in 4,5-dihydrooxepines which are amenable to hydrolysis, furnishing 1,6-dicarbonyl compounds containing two contiguous stereocenters at the 3- and 4-positions. We employ an Ir-based alkene isomerization catalyst to form the reactive 2,3-divinyloxirane in situ with complete regio- and stereocontrol, which translates into excellent control over the stereochemistry of the resulting oxepines and ultimately to an attractive strategy towards 1,6-dicarbonyl compounds.

Iridium catalyzed alkene isomerization-cope rearrangement of ω-diene epoxide furnishes 3,4-dihydrooxepines. These oxepines are hydrolyzed to diastereomerically pure 1,6-dicarbonyl compound containing two contiguous stereocenters within acyclic system.

1,6-Dicarbonyl compounds are widespread as targets and intermediates in organic synthesis.1 Due to the “dissonant” polarizing effect induced by the two carbonyl groups,2 these motifs are challenging to retrosynthetically disconnect into classical synthons. Unsurprisingly, many approaches toward 1,6-dicarbonyls rely on dimerization of α,β-unsaturated carbonyl compounds (Scheme 1a)3 or oxidative cleavage of substituted cyclohexene derivatives4 which significantly limits the range of possible products. Alternative strategies, such as the ring-opening of donor–acceptor cyclopropanes with enolate nucleophiles, efficiently form the 1,6-dicarbonyl skeleton, albeit with limited substrate scope (Scheme 1b).5 The Cope rearrangement of 1,5-dienes, featuring oxygen functionality in the 3- and 4-positions,6 represents a promising strategy towards 1,6-dicarbonyl compounds but suffers from lack of stereocontrol over the diene substrates, resulting in diastereomeric mixtures of products (Scheme 1c).Open in a separate windowScheme 1Selected approaches towards the formation of 1,6-dicarbonyl compounds and our proposed approach.A conceptually related approach towards the preparation of 1,6-dicarbonyl compounds is through the hydrolysis of 3,4-dihydrooxepines (Scheme 1d), which are in turn generated through the Cope rearrangement of 2,3-divinyloxiranes.7 Such a sigmatropic rearrangement is also noteworthy as a rare example where an epoxide C–C bond is selectively cleaved over the usually more reactive C–O bond. This intriguing rearrangement has been studied but its use in synthesis is scarce, presumably due to difficulties in the stereoselective synthesis and handling of the key divinyl epoxides.In line with our interest in the strategic application of alkene isomerization to generate reactive synthetic intermediates in stereodefined form,8 we posited to form the reactive 2,3-divinyloxiranes in situ, through alkene isomerization9,10 of the simpler allyl epoxides, which are accessible in enantiomerically enriched form.11 Such a strategy might greatly facilitate access to these intermediates and therefore uncover a synthetically attractive route toward 1,6-dicarbonyl compounds featuring two contiguous stereocenters.With this idea in mind, we first explored the isomerization and subsequent Cope rearrangement of allyl-vinyl epoxides 1 (Scheme 2). To induce isomerization, we employed a cationic iridium-based catalytic system,12 which is known to reliably isomerize alkenes with high degrees of regio- and stereocontrol.13Open in a separate windowScheme 2Substrate scope for the tandem iridium-catalyzed alkene isomerization-Cope rearrangement of allyl-vinyl epoxides.In line with our expectations, our model substrate 1a (R2 = R3 = H, R4 = Me, R5 = CO2Et) was smoothly isomerized at 65 °C in the presence of 1.5 mol% of Ir dimer to obtain the corresponding divinyl epoxide with a complete E-selectivity. With suitable conditions for alkene isomerization in hand, we exposed substrate 1a to the Ir-based catalytic system at 120 °C and were equally pleased to observe the 4,5-dihydrooxepine product 2a, resulting from the tandem isomerization-Cope rearrangement as a single diastereoisomer in 81% yield. We proceeded to test the generality of our protocol with respect to different alkene and epoxide substitution patterns. Pleasingly, product 2b was generated with complete stereoselectivity, showcasing the compatibility of the reaction conditions with potentially labile tertiary stereocenters α to the ester group. We then wondered whether the anti-diastereomer could be accessed starting from the corresponding cis allyl-vinyl epoxide. Indeed, in line with the known stereospecific behavior of the Cope rearrangement, we obtained the complementary diastereomer 2c. Turning our attention to more highly substituted epoxides, we were pleased to observe the formation of dihydrooxepines 2d and 2e, which correspond to 1,6-keto-aldehyde and diketone products, respectively. Substrate 1f (R2 = R4 = R5 = H, R3 = Ph), which features an unactivated vinyl group, also underwent the rearrangement, demonstrating that an activated alkenyl group is not required for a successful outcome. Similarly, product 2g featuring two alkyl groups is also generated, with high diastereoselectivity albeit in moderate yield. Products featuring ethyl and methyl ester 2h, 2i could also be obtained in good yields and diastereoselectivity. We next tested substrate 1j (R2 = Me, R3 = Ph, R4 = CH2CH2Ph, R5 = H), as a geometric-mixture of the double bond (E : Z = 1.1 : 1) and in accordance with the stereospecificity of the process, the oxepine 2j was obtained as a mixture of two diastereomers with the same ratio. Disappointingly, substrate 1k did not undergo isomerization, presumably due to the Lewis basic nature of the ketone, likely poisoning the Ir-catalyst.During our study, we noticed that allyl-vinyl epoxides bearing electron donating groups on the vinyl moiety tend to decompose during purification by column chromatography on silica gel. This obstacle further motivated us to explore diallyl epoxides 3 as substrates, where the reactive divinyl epoxide would be generated by isomerization of both allyl fragments. Notably, these diallyl epoxides are much more stable compared to their vinyl counterparts and can be readily prepared in two steps from simple alkynes.14 To our delight, diallyl epoxide 3a (R = CH2OMe) smoothly underwent the double isomerization-Cope rearrangement cascade at 140 °C, furnishing oxepine 2l with impressive yield and diastereoselectivity (Scheme 3). The use of alkene isomerization to form the reactive divinyl epoxide in situ avoids the isolation of the unstable divinyl epoxide, while controlling the stereochemistry of both double bonds, particularly not trivial to achieve using classical olefination reactions. Products 2m and 2n feature ester and silyl groups, highlighting the functional group tolerance of the catalytic system.Open in a separate windowScheme 3Substrate scope for tandem iridium-catalyzed double alkene isomerization-Cope rearrangement of diallyl epoxides.Our next objective was to hydrolyze the diastereomerically pure oxepines obtained through the rearrangement in a stereoretentive fashion, revealing the acyclic 1,6-dicarbonyl motif. Pleasingly, diversely substituted oxepines 2 underwent smooth hydrolysis either using 5 mol% of Pd(MeCN)2Cl215 at 50 °C or an acidic aqueous solution to form 1,6-dicarbonyls 4 in diastereomerically pure form (Scheme 4).16 Dicarbonyl products featuring labile tertiary centers 4a and 4b are formed under these conditions with excellent diastereoselectivities and yields. Without surprise, oxepine 2f (R2 = R4 = R5 = H, R3 = Ph) furnished the keto-substituted product 4c in good yield. The relative stereochemistry of 4b was unambiguously confirmed by single crystal X-ray diffraction analysis of the corresponding carboxylic acid 7 (Scheme 4b).17 The reaction is scalable to ½ gram of substrate and could be performed in a single-pot operation without isolation of the intermediate oxepine (Scheme 4b). By using this approach, 1h provides 4b in 61% yield as a single diastereomer, underlining the synthetic potential and efficiency of this method.Open in a separate windowScheme 4Hydrolysis of oxepines and one-pot sequence.  相似文献   

15.
Skeleton Rearrangement of an α-β-Unsaturated γ,δ-Epoxyketone during Birch Reduction: Structure Elucidation by Means of 13C-INADEQUATE-NMR Spectroscopy When the γ-epoxide 2 of β-ionone is treated under standard Birch-reduction conditions, unexpectedly a 70% combined yield of regioisomeric octalones 4 and 5 is isolated. These products unquestionably result form cleavage of the central epoxide C?C bond. The structure of compounds 4 and 5 could be determined by means of 13C-INADEQUATE-NMR spectroscopy.  相似文献   

16.
Stability in Methanol and Thermodynamic Transfer Properties of the Cryptates of some Transition Cations and Heavy Metals The nature and stability of the macrocyclic and macrobicyclic complexes of Ag+, Cd2+, and Pb2+ (Mn+) with 21, 22, 211, 221 and 222 in anhydrous methanol 0.05M in Et4N+ClO?4, at 25° (see Scheme) have been determined by potentiometry and spectrophotometry. Binuclear complexes M2L2n+ have been observed in all cases, besides the mononuclear MLn+ complexes. The macrobicyclic 1:1 complexes MLn+ exhibit an important ‘cryptate effect’ with Mn+=Ag+, Pb2+ and Cd2+, but not with Cu2+ and Zn2+; their stability is in all cases maximum with 221. The applicability to our results of the recent extrathermodynamic hypothesis involving MLn+ cryptates is examined.  相似文献   

17.
A 13C NMR study of a series of methyl sulphur compounds is described. The results are discussed in terms of the deshielding effects on the methyl carbon exerted by –SH, –SMe, –SSMe, –SSEt, –SSMe, –SC(O)Me, –SC(S)Me, –SC(S)SMe. The 13C NMR chemical shifts of a series of S-methyl thioesters and dithioesters are compared with corresponding esters and connected with chemical properties.  相似文献   

18.
A rate constant for the epoxidation of acrolein by acetylperoxyl radicals has been determined to be k4 = (1.3 ± 0.9) × 104 dm3mol−1s−1 at 383 K, which is anomalously fast in comparison with the epoxidation of alkenes. Abstraction of the acyl hydrogen atom from acrolein by acetylperoxyl radicals at 393 K was found to be at least 60 times slower than from acetaldehyde and at least three orders of magnitude slower than abstraction of the acyl hydrogen atom of the epoxide of acrolein. The fast rate for epoxidation of acrolein and the slow rate for hydrogen abstraction provide an explanation for the anomalously slow rate for the autoxidation of acrolein and suggests that acrolein formed during the autoxidation of alkene will react further to give its epoxide, and not exclusively by abstraction of the acyl hydrogen atom as was previously accepted. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 277–282, 1999  相似文献   

19.
The mechanism and kinetics of curing reaction of tetrafunctional epoxy resin (Ag-80)/novel diamines curing (SED) system were studied by non-isothermal and isothermal DSC. Different equivalent ratios of amine-epoxide give rise to different curing mechanisms. The main condensation reaction can be attributed to the reactions between the primary amine and epoxide and between the hydroxyl and epoxide when temperature is below 200°C, and to the reaction between the second-ary amine and epoxide when temperature is above 200°C. The corresponding apparent activation energies are 58.3 kJ·mol?1 and 99.3 kJ·mol?1 respectively. Apparent activation energies of condensation reactions between primary amine and epoxide and between hydroxyl and epoxide are just the same, which are 47.3 kJ·mol?1.  相似文献   

20.
Derivatives of enose- and ynosephosphonates and related compounds. Preliminary communication The gem-dibromo terminal enoses 1 and 7 are convenient sources of glycosylacetylenes which upon reaction with phosphorus electrophiles gave the phosphorusbearing acetylenic sugars 4, 5 and 8 . Compounds 5 and 8 underwent cycloaddition reactions leading to isoxazolyl-C-glycosides 6 and 9 respectively. The nitroolefinic sugar derivative 11 gave upon bromination-dehydrobromination the first example of a new kind of potentially useful synthetic intermediates, the gem-bromonitroenose 12 . The enosephosphonate 13 was also prepared from 11 . The diglycosylhydroxylamine 18 represents another type of phosphorus-bearing acetylenic sugar derivative. Some 1H- and 13C-NMR. data relative to the new types of phosphorus-containing sugar derivatives synthesized are given.  相似文献   

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