The thermal conversion of 4‐isoxazolines to 4‐oxazolines involves the transposition of two ring members. The ring‐contraction and ring‐expansion sequence in the reaction 2 → 5 has been previously clarified. The low N−N bond energy should favor an analogous conversion of 3‐pyrazolines 6 to 4‐imidazolines 7 ; the first example of such a transformation is reported here. In the yellow 16 , the 3‐pyrazoline is part of a pyrazolo[5,1‐a]isoquinoline system. Daylight induces a ring contraction, which affords the 2‐isoquinolylaziridine derivative 21 . The latter is converted at 65° to the tricyclic 4‐imidazoline 26 by a sequence of electrocyclic aziridine ring‐opening and 1,5‐electrocyclization of a C=N‐conjugated azomethine ylide 25 . 相似文献
The enantioselective desymmetrization of the prochiral 3-O-silyl protected pentanetriol derivative 3 was carefully investigated. At −10 °C, the bacterial lipase from Burkholderia cepacia immobilized on ceramic particles led to monoacetate (S)-4 in 52% yield and >99.9% ee. At a reaction temperature of −40 °C the yield and enantioselectivity were even higher, but the reaction time was very long. Theoretical simulations of the reaction progress indicated an enantioselectivity of 25:1 at −10 °C and 35:1 at −40 °C. (S)-4 was converted into the enantiomerically pure building block 5-azidopentane-1,3-diol (S)-7 in two steps. The absolute configuration of (S)-7 was determined by exciton-coupled circular dichroism (ECCD) of diester (S)-8. 相似文献
Summary: Based on the fact that rubber can be chemically modified by sulfur, and sulfur can diffuse into rubber driven by a concentration gradient and chemical reaction, a new approach for the preparation of a polymer with a gradient from rubbery to glassy phase has been developed using the sulfur‐vulcanization reaction of rubber. The gradient polymer obtained exhibits a wide transition range spanning over 100 °C with a peak half‐width of 69 °C. The mechanism of forming the gradient structure is also discussed.
The gradient polymer exhibits a broad tan δ width from −60 to 76 °C with the peak half‐width spanning about 69 °C, indicating a wide damping temperature range. 相似文献
An efficient, convergent approach for the total synthesis of aigialomycin D 1 is described. Key features of the synthetic strategy include (a) a Sharpless asymmetric epoxidation reaction and selective opening of a 2,3-epoxy alcohol to elaborate the two hydroxy-bearing stereogenic centers at the C5′ and C6′ positions; (b) a Kocienski modified Julia protocol to construct the two E-configured double bonds; and (c) Yamaguchi macrolactonization to acccess the 14-membered macrocyclic ring. 相似文献
The reaction of perfluoro(1-phenyl-1,2-diethyl-1,2-dihydrocuclobutabenzene) with SbF5 at 20°C, followed by treatment of the
reaction mixture with water gave perfluoro {4-[1-(2-propylphenyl)propylidene]-2,5-cyclohexadien-1-one} together with perfluoro[4b,10-diethylbenzo[a]azulen-7(4bH)-one] resulting from unusual expansion of the pentafluorobenzene ring to seven-membered ring. Analogous reaction at 90°C,
apart from the above compounds, afforded perfluorinated 10-ethyl- and 3,10-diethylbenzo[a]azulen-6(10H)-ones via elimination of C2F5 group from the seven-membered ring or its migration to the benzene ring. 相似文献
We report the first chemical synthesis of eurysterol A, a cytotoxic and antifungal marine steroidal sulfate with a unique C8−C19 oxy-bridged cholestane skeleton. After C19 hydroxylation of cholesteryl acetate, used as an inexpensive commercial starting material, the challenging oxidative functionalization of ring B was achieved by two different routes to set up a 5α-hydroxy-7-en-6-one moiety. As a key step, an intramolecular oxa-Michael addition was exploited to close the oxy-bridge (8β,19-epoxy unit). DFT calculations show this reversible transformation being exergonic by about −30 kJ mol−1. Along the optimized (scalable) synthetic sequence, the target natural product was obtained in only 11 steps in 5 % overall yield. In addition, an access to (isomeric) 7β,19-epoxy steroids with a previously unknown pentacyclic ring system was discovered. 相似文献
Polyamideamines with a sequence of two amide and one amine linkage in a main chain were synthesized from the polyaddition of 2-isopropylidene-4-alkyl-3-oxazolin-5-ones and primary diamines. The polyaddition reaction proceeded through 1,4-conjugate addition of an amine group to 3-oxazolin-5-one and subsequent ring opening of the intermediate addition product with another amine. Although aliphatic diamines gave oily polymers, xylylenediamines afforded amorphous solid polymers. The reduced viscosities and polymer melt temperature of the polymers were 0.05–0.12 and 90–130°C., respectively. 相似文献
In the system KrF2—MnF2—HF two new adducts, 2KrF2·MnF4 and KrF2·MnF4 have been synthesized. The 2 : 1 adduct decomposes in a dynamic vacuum at −45°C yielding KrF2 and the 1 : 1 adduct, which is stable in a dynamic vacuum up to −25°C. KrF2·MnF4 decomposes further at room temperature to krypton, fluorine, krypton difluoride and manganese tetrafluoride. This reaction is a useful synthetic route for the preparation of pure manganese tetrafluoride. 相似文献
3,6-Dimethoxybenzocyclobutenone 4 is prepared in four efficient steps from 2,5-dimethoxybenzoic acid 8. The derived benzocyclobutenol 13 undergoes electrocyclic ring opening at 110–115°C to give the hydroxy-o-quinone dimethide 21, which reacts with dienophiles to give 5,8-dimethoxy-1,2,3,4-tetrahydro-1-naphthol derivadves stereoselecdvely. Since the ketone 4 can be functionalised at C-5 using electrophiles and at C-2 via hoimolytic bromination, the ring opening and cycloaddition sequence offers a flexible route to linear fused hydroquinone and quinone derivatives. In model studies, the benzocyclobutenol derivative 48 underwent thermal electrocyclic ring opening and intramolecular cycloaddition to give 49, while the analogous reaction with 52 failed due to adverse steric effects during the cycloaddition step. In photochemical experiments, attempts to generate the silyi ether 57 by in situ silylation of the dienol 55 and to prepare the benzocyclobutenol 62 via irradiation of the o-phthalaldehyde monoacetal 60 were unsuccessful. 相似文献
Size-fractionated aerosol particles were collected with a MOUDI 10-stage cascade impactor from an urban roadside place in a downtown area of Hong Kong. Fine aerosol particulate samples from stage 6 (aerodynamic particle diameter between 0.56 and 1 μm) and stage 9 (aerodynamic particle diameter between 0.10 and 0.18 μm) were pretreated at a chosen temperature, including −100°C, −50°C, 25°C, and 60°C, in a load lock chamber and then analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS) at the same temperature (−100°C). Principal component analysis (PCA) was applied to further analyze ToF-SIMS spectra of aerosol particles with different pretreatment temperatures from two selected stages. ToF-SIMS results showed that the intensities of aliphatic hydrocarbon ions such as C4H7+ and C4H9+ and amine ions such as C2H8N+ and C4H12N+ decreased with an increase of the pretreatment temperature under ultrahigh vacuum conditions. We have shown that analyses of this type of aerosol particles using ToF-SIMS should not be conducted at ambient temperature but at low temperature (eg, −50°C). In addition, we also developed a procedure that can be used to analyze aerosol particle samples under ultrahigh vacuum environment. 相似文献
Anionic polymerization of N-methacryloyl-2-methylaziridine ( 1 ) proceeded with 1,1-diphenyl-3-methylpentyllithium (DMPLi) in the presence of LiCl or Et2Zn to give the polymers possessing predicted molecular weights and narrow molecular weight distributions (Mw/Mn < 1.1) at −78 ∼ −40 °C in THF. In each polymerization initiated with DMPLi/LiCl at the various temperatures ranging from −40 to −60 °C, the linear relationship between polymerization time and conversion of monomer was obtained from the GLC analysis. The rate constant and the activation energy of the anionic polymerization for 1 were determined as follows: ln k = −5.85 × 103/T + 23.3 L mol−1 s−1 and 49 ± 4 kJ mol−1, respectively. Poly( 1 ) showed the glass transition temperature at 98 °C, and gave the insoluble product at higher temperature around 150 °C through the thermal cross-linking of highly strained N-acyl-aziridine moiety. 相似文献
Edoxaban was extracted from human plasma by simple protein precipitation with acetonitrile, followed by quantitative determination using a liquid chromatography–mass spectrometry method. The recoveries of edoxaban and the internal standard (ticlopidine) from human plasma were >85%, and the within‐ and between‐day coefficients of variation were within 15%. The limit of quantification in human plasma was 1 ng/mL. The concentration of edoxaban in blood decreased at room temperature, but remained unchanged for 1 week at 4°C. On the other hand, the concentration in plasma at both −20 and −80°C remained unchanged for 5 months. These results indicated that blood samples should be centrifuged immediately or stored at 4°C, and that plasma samples should be stored below −20°C until analysis. This method was applied to human plasma obtained from four patients after total knee arthroplasty. Analysis of edoxaban pharmacokinetics demonstrated an absorption time lag of 4h, a maximum concentration of 110 ± 26 ng/mL and an oral clearance of 37 ± 16 L/h. The analytical methods established in this study will be suitable for determining the concentrations of edoxaban in human plasma. 相似文献
Conclusions When 1,2,8,9-diepoxy-p-menthane is reacted with HCl in ether under mild conditions, the 1,2-epoxy ring opens first in accordance with the conformational control of the reaction to form (–)-trans-2-hydroxy-1-chloro-8, 9-epoxy-trans-p-menthane from the cis dioxide or (–)-trans-1-hydroxy-2-chloro-8, 9-epoxy-trans-p-menthane from the trans dioxide. The opening of the 8,9-epoxy ring to form products of the addition of 2 moles of HCl takes place with difficulty.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 847–851, April, 1979. 相似文献
The title compound, C13H24O11·4H2O, (I), crystallized from water, has an internal glycosidic linkage conformation having ϕ′ (O5Gal—C1Gal—O1Gal—C4All) = −96.40 (12)° and ψ′ (C1Gal—O1Gal—C4All—C5All) = −160.93 (10)°, where ring‐atom numbering conforms to the convention in which C1 denotes the anomeric C atom, C5 the ring atom bearing the exocyclic hydroxymethyl group, and C6 the exocyclic hydroxymethyl (CH2OH) C atom in the βGalp and βAllp residues. Internal linkage conformations in the crystal structures of the structurally related disaccharides methyl β‐lactoside [methyl β‐d ‐galactopyranosyl‐(1→4)‐β‐d ‐glucopyranoside] methanol solvate [Stenutz, Shang & Serianni (1999). Acta Cryst. C 55 , 1719–1721], (II), and methyl β‐cellobioside [methyl β‐d ‐glucopyranosyl‐(1→4)‐β‐d ‐glucopyranoside] methanol solvate [Ham & Williams (1970). Acta Cryst. B 26 , 1373–1383], (III), are characterized by ϕ′ = −88.4 (2)° and ψ′ = −161.3 (2)°, and ϕ′ = −91.1° and ψ′ = −160.7°, respectively. Inter‐residue hydrogen bonding is observed between O3Glc and O5Gal/Glc in the crystal structures of (II) and (III), suggesting a role in determining their preferred linkage conformations. An analogous inter‐residue hydrogen bond does not exist in (I) due to the axial orientation of O3All, yet its internal linkage conformation is very similar to those of (II) and (III). 相似文献
The reaction of the epoxysteroids 1 and 4, derived from estrone and cholestanone, respectively, with an excess of lithium and a catalytic amount of DTBB (7 mol%) in THF at −78°C, leads to the formation of the corresponding β-oxido-functionalised organolithium intermediates 2 and 5, respectively, which, by reaction with different electrophiles [H2O, D2O, PhCHO, Me2CO, Et2CO, (CH2)5CO, CO2] at −78°C to room temperature, afford, after hydrolysis with water, enantiomerically pure compounds 3 and 6, respectively. The stereochemistry of all these compounds was unambiguously determined by correlation with X-ray data for compound 3d and by comparison with the known compound 6a. 相似文献
On treatment with 6 mol-equiv. of lithiomethyl phenyl sulfone at −78° in THF, dimethyl 5,6,8,10-tetramethylheptalene-1,2-dicarboxylate ( 1′b ) gives, after raising the temperature to −10° and addition of 6 mol-equiv. of BuLi, followed by further warming to ambient temperature, the corresponding 3-(phenylsulfonyl)benzo[a]heptalene-2,4-diol 2b in yields up to 65% (cf. Scheme 6 and Table 2), in contrast to its double-bond-shifted (DBS) isomer 1b which gave 2b in a yield of only 6% [1]. The bisanion [ 9 ]2− of the cyclopenta[a]heptalen-1(1H)-one 9 (cf. Fig. 1), carrying a (phenylsulfonyl)methyl substituent at C(11b), seems to be a key intermediate on the reaction path to 2b , because 9 is transformed in high yield into 2b in the presence of 6 mol-equiv. of BuLi in the temperature range of −10° to room temperature (cf. Scheme 7). Heptalene-dicarboxylate 1′b was also transformed into benzo[a]heptalene-2,4-diols 2c – g by a number of lithiated methyl X-phenyl sulfones and BuLi (cf. Scheme 9 and Table 3). 相似文献