Enantioselective Total Synthesis of Pseudopteroxazole and Ileabethoxazole

Enantioselective total syntheses of pseudopteroxazole ( 1 ) and ileabethoxazole ( 2 ) are presented. The two original stereocenters were constructed in excellent enantioselectivity and good diastereoselectivity through Carreira's asymmetric dual catalytic allylation, which shows potential for accessing diastereoisomers at C2 and C3 of 1 and 2 . Cationic cyclizations of 13 and 24 demonstrated an effective pathway for the construction of the opposite configurations at C1 in 1 and 2 . Additionally, an approach for the introduction of methyl at C4 is a feasible solution for structural modifications at C4 in 1 and 2 .     

Surface tension of binary mixtures of imidazolium and ammonium based ionic liquids with alcohols, or water: cation, anion effect

The surface tensions were measured at atmospheric pressure, with use of a ring tensiometer, of a series of alcoholic solutions of closely related ionic liquids: 1-methyl-3-methylimidazolium methylsulfate, [MMIM][CH3SO4] in alcohol (methanol, or ethanol, or 1-butanol at 298.15 K), 1-butyl-3-methylimidazolium methylsulfate, [BMIM][CH3SO4] in alcohol (methanol, or ethanol, or 1-butanol at 298.15 K), 1-butyl-3-methylimidazolium octylsulfate, [BMIM][OcSO4] in alcohol (methanol, or 1-butanol at 298.15 K) and of 1-hexyloxymethyl-3-methylimidazolium tetrafluoroborate, [C6H(13)OCH2MIM][BF4], 1,3-dihexyloxymethylimidazolium tetrafluoroborate, [(C6H13OCH2)2IM][BF4] in alcohol (methanol, or 1-butanol, or 1-hexanol at 308.15 and 318.5 K) and hexyl(2-hydroxyethyl)dimethylammonium bromide, C6Br in 1-octanol at 298.15 K. The set of ammonium ionic liquids of different cations and anions (C2Br, C2BF4, C2PF6, C2N(CN)2, C3Br, C4Br and C6Br) was chosen to show the influence of small amount of the ammonium ionic liquid on the surface tension of water at 298.15 K. The influence of the cation, or anion alkyl chain length on the properties under study (densities and surface tension) was tested.     

Conformational study of 1,2-cycloundecadiene by dynamic NMR spectroscopy and computational methods

Solutions of 1,2-cycloundecadiene in propane were studied by low-temperature (13)C NMR spectroscopy. A total of 17 peaks were observed at -166.7 degrees C, corresponding to two conformations of similar populations, one of C(1) symmetry (11 peaks) and the other of C(2) symmetry. The line shapes show that the predominant pathway for exchange of the topomers (C(1) and C(1)') of the C(1) conformation does not include the C(2) conformation. From the (13)C spectra, free-energy barriers of 8.38 +/- 0.15, 9.45 +/- 0.15, and 9.35 +/- 0.15 kcal/mol were determined for the C(1) to C(1)', (C(1) + C(1)') to C(2), and C(2) to (C(1) + C(1)') conversions, respectively, at -72.2 degrees C. The NMR results for this compound are discussed in terms of the conformations predicted by molecular mechanics calculations obtained with Allinger's MM3 program. Ab initio calculations of free energies are also reported at the HF/ 6-311G level for 25 conformations.     

Unexpected shielding of methyl group protons in some piperidines

High resolution 1H and 13C NMR spectra of four 3-ethyl-4-hydroxy- 4-phenylpiperidines 1-4 have been recorded in CDCl3 and analysed. The conformations of phenyl and hydroxyl groups at C(4) and ethyl group at C(3) were analysed in detail. The chemical shift of the methyl protons in the ethyl group are quite surprising; they are close to TMS in CDCl(3) and even negative in DMSO-d6. These results are interpreted in terms of the magnetic anisotropy of the phenyl rings at C(2) and C(4) which, in turn, depend on the conformations of the ethyl group at C(3) and the hydroxyl group at C(4). Favoured conformations of ethyl group at C(3) and hydroxyl group at C(4) were calculated by AM1 methods.     

石墨烯掺杂LiFePO4电极材料的合成及其电化学性能

采用水热辅助法合成石墨烯改性的LiFePO4多孔微球电极材料.并对材料进行了X射线衍射(XRD),扫描电子显微镜(SEM),透射电子显微镜(TEM),傅里叶变换红外(FT-IR)光谱,充放电等表征.从结果可以看出在2 mol·L-1LiNO3电解液体系中单纯包碳的LiFePO4微球在1C、50C倍率时的比容量分别为137、64 mAh·g-1,而石墨烯改性的LiFePO4微球的比容量分别为141、105 mAh·g-1,表现出较好的倍率特性.恒流循环充放电测试60次后两种材料容量保持率分别为70.2％、83.7％.说明掺杂石墨烯构成的三维导电网络能明显改善LiFePO4的电化学性能.     

Diversity-oriented asymmetric synthesis of hapalosin: construction of three small C9/C4/C3-modified hapalosin analogue libraries

A flexible approach to the beta-hydroxy gamma-amino acid residue (fragment C) of hapalosin has been developed on the basis of the the regio- and diastereoselective Grignard reaction. The method allows the introduction of different side chains at the C9 of hapalosin. Asymmetric syntheses of hapalosin (1a), 9-homohapalosin (1b), 9-i-butyl-hapalosin (1c), 8-epi-hapalosin (epi-1a), and three small libraries diversified at C9 (3-member, 1L3), C9/ C4 (9-member, 1L9), or C9/C4/C3 (27-member, 1L27) have been produced using this method.     

锂离子电池正极材料LiMnPO_4/C的合成研究

以间苯二酚甲醛树脂作碳源,由固相法合成LiMnPO4/C复合材料.研究不同合成温度和时间对产物形貌、结构以及电化学性能的影响.结果表明,600℃热处理3 h制得的LiMnPO4/C粒径细小且分布均匀,一次颗粒粒径100～300 nm.0.02C下首次放电容量达到121.6 mAh.g-1,充放电循环20次仍可维持在11...     

Methodology for the preparation of C1-monoalkylated 1,2-dihydro[C70)] derivatives: formation of the "other" regioisomer

Deprotonation of 1,2-C(70)H(2) with TBAOH, followed by alkylation with methyl bromoacetate, results in formation of a C1-monoalkylated 1,2-dihydro-C(70) derivative. The position of the alkyl group (C1) was established by NMR spectroscopy and comparison with literature spectra of C2-monoalkylated analogs. Presumably, C1-alkylation is the major process due to selective deprotonation of 1,2-C(70)H(2) at C1. Substitution of benzyl bromide for methyl bromoacetate results in rapid dialkylation, unless the amount of base is carefully controlled, in which case C1-monobenzylation is the major process. This methodology for alkylation at C1 is complimentary to methods for the C2-monoalkylation of C(70) with Zn and methyl bromoacetate.     

Solvent-dependent regioselectivity of hydrogen chloride-mediated ring opening of alkylidenecyclopropanone acetal

Ring opening reactions of 2-cyclohexylidene-3,3-dimethylcyclopropanone acetal (1) are readily induced by treatment of hydrogen chloride in various solvents. Bond cleavage takes place at the C1-C2 or C2-C3 bond, and the ratio of C1-C2/C2-C3 cleavages changes from >99/1 to <1/99 depending on the solvent. The two modes of bond cleavage must be initiated by protonations at the carbon-carbon double bond and the acetal oxygen, respectively. The regioselectivity can be rationalized by the rate-determining protonation at carbon and the equilibrium protonation at oxygen.     

Thermal and stability study of tetracene using differential scanning calorimetry

A thermal analysis study was made of tetracene using differential scanning calorimetry (DSC). The effect of different scan speeds was investigated. At scan speeds of 0.625 to 10°C min^?1 two large rounded exothermic peaks were produced. The peaks occurred at an increasingly high temperature as the scan speed increased (for example, the peaks occurred at 128 and 130°C at a scan speed of 0.625°C min^?1 and at 148 and 150°C at a scan speed of 10°C min^?1. When tetracene was heated at a scan speed of 80°C min^?1 only one large sharp exothermic peak was produced. It is believed that the two peaks obtained at scan speeds of 0.625 to 10°C min^?1 represent decomposition of the tetracene in two successive stages, while the one peak obtained at 80°C min^?1 represents an explosion. A stability test for tetracene is proposed that involves heating of the tetracene in aluminum pans from the DSC apparatus in ovens at 100, 75, and 60°C, removing the pans and samples at intervals of 30 min, 24 h, and 7 days, respectively, subjecting the samples to DSC at 1.25°C min^?1, and noting the time interval in the oven that produces a DSC curve that shows obliteration of the second peak. Two lots of tetracene made by different processes showed marked differences in stability characteristics.     

Isotopic study of new fundamentals and combination bands of linear C5, C7, and C9 in solid ar

A high yield of carbon chains has been produced by the laser ablation of carbon rods having (13)C enrichment. FTIR spectroscopy of these molecules trapped in solid Ar has resulted in the identification of two new combination bands for linear C(5) and C(9). The (ν(1) + ν(4)) combination band of linear C(5) has been observed at 3388.8 cm(-1), and comparison of (13)C isotopic shift measurements with the predictions of density functional theory calculations (DFT) at the B3LYP/cc-pVDZ level makes possible the assignment of the ν(1)(σ(g)(+)) stretching fundamental at 1946 cm(-1). Similarly, the observation of the (ν(2) + ν(7)) combination band of linear C(9) at 3471.8 cm(-1) enables the assignment of the ν(2)(σ(g)(+)) stretching fundamental at 1871 cm(-1). The third and weakest of the infrared stretching fundamentals of linear C(7), the ν(6)(σ(u)(+)) fundamental at 1100.1 cm(-1), has also been assigned.     

Reactions of Allyl Phenyl Ether in High-Temperature Water with Conventional and Microwave Heating

In a systematic study, allyl phenyl ether (1) was heated in water for 1 h at temperatures of 180 degrees C and above. Parallel experiments were conducted with a conventionally heated autoclave and a recently developed microwave batch reactor. Relatively modest temperature differences resulted in diverse product distributions, and these were independent of the method of heating. Maximum conversion of 1 to 2-allylphenol occurred at 200 degrees C (56%) and to 2-methyl-2,3-dihydrobenzofuran at 250 degrees C (72%). Although 2-(2-hydroxyprop-1-yl)phenol comprised less than 1% of the product mixture at both 180 and 260 degrees C, it accounted for 37% at 230 degrees C. The reaction sequence was investigated by heating intermediates individually at selected temperatures up to 290 degrees C. Hydration of 2-allylphenol to 2-(2-hydroxyprop-1-yl)phenol was partially reversible. The work showed that high-temperature water constitutes an environmentally benign alternative to the use of acid catalysts or organic solvents and offers scope for interconversion of alcohols and alkenes.     

Semisynthesis of Some 7-Deoxypaclitaxel Analogs from Taxine B

Taxine B (3), isolated from the dried needles of Taxus baccata, was converted into six novel 7-deoxypaclitaxel analogs, 20, 21a,b, and 23-25, that have structural changes at C1, C2, and C4. A method for the introduction of the benzoyl function at C2, via a benzylidene acetal at C1-C2, will be revealed. All compounds showed very little or no measurable cytotoxic activity against some well-characterized human tumor cell lines, probably due to the nonacylated hydroxyl group at C4.     

Facile synthesis of reactive benzoazetinone by flash vacuum pyrolysis of isatoic anhydride

Pyrolysis of isatoic anhydride (3) at 550°C and ca. 1×10⁻² torr gave benzoazetinone (1, 80%) as the only product. The existence of 1 was confirmed by low-temperature NMR spectroscopy at −90°C. Above −20°C, 1 was converted to dimer (4, 50%), trimer (5, 22%), and anthranilic acid (6, 12%). Pyrolysis of 3 at 800°C and ca. 1×10⁻² torr gave 1-cyanocyclopentadiene (7) in 38% yield.     

Effect of methoxyl groups on the NMR spectra: configuration and conformation of natural and synthetic indanic and tetralinic structures

Here, we studied the influence of the methoxyl groups attached at C‐7 and C‐2′ of natural and synthetic 1‐arylindanes on the chemical shift of the signal of bibenzylic hydrogen and carbon atoms and J_1,2 coupling constants. This influence was also analysed in natural 1‐aryltetralins and related compounds that possess methoxyl and/or hydroxyl groups bound at C‐8 and C‐2′. The methoxyl groups attached at C‐7 in indanes or at C‐8 in tetralins produce a deshielding signal at H‐1 and shield at C‐1 and a strong decrease in the value of J_1,2 due to the pseudoequatorial location adopted by the aryl group bound at C‐1, avoiding an ‘A^1,3 strain’. Furthermore, compounds with hydroxyl or methoxyl groups in C‐2′, in the absence of substituents of C‐7 or C‐8, present a strong deshielding signal at H‐1, strong shield of the C‐1 signal and a decrease in the value of J_1,2. This is attributed to the stereoelectronic effects of the methoxyl or hydroxyl groups, which we have called ‘Asarone effect’. NOESY experiments were conducted to confirm the configuration and conformation of some of the compounds included in this work. This study shows that both effects, A^1,3 strain and Asarone effect, must be taken into account when the structure of natural indanes and tetralins is analysed by using ¹H‐NMR and ¹³C‐NMR spectra. Copyright © 2016 John Wiley & Sons, Ltd.     

Efficient syntheses of rugulosin analogues

Oxidation of 3b or 14c,d with Pb(OAc)4 in AcOH for 20 min at 25 degrees C and 1 h at 75 degrees C gave flavoskyrin-type dimers 6b and 15c,d in 53-86% yield. Heating a solution of 6b or 15c,d in pyridine under air for 1 h at 75-80 degrees C and then for 1-2 h at 110 degrees C afforded rugulosin-type dimers 10b and 17c,d in 61-88% yield. This two-step sequence provides a practical route to this unusual natural product skeleton.     

Infrared absorption of gaseous benzoyl radical C6H5CO recorded with a step-scan Fourier-transform spectrometer

A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the gaseous transient species benzoyl radical, C(6)H(5)CO. C(6)H(5)CO was produced either from photolysis of acetophenone, C(6)H(5)C(O)CH(3), at 248 nm or in reactions of phenyl radical (C(6)H(5)) with CO; C(6)H(5) was produced on photolysis of C(6)H(5)Br at 248 nm. One intense band at 1838 ± 1 cm(-1), one weak band at 1131 ± 3 cm(-1), and two extremely weak bands at 1438 ± 5 and 1590 ± 10 cm(-1) are assigned to the C═O stretching (ν(6)), the C-C stretching mixed with C-H deformation (ν(15)), the out-of-phase C(1)C(2)C(3)/C(5)C(6)C(1) symmetric stretching (ν(10)), and the in-phase C(1)C(2)C(3)/C(4)C(5)C(6) antisymmetric stretching (ν(7)) modes of C(6)H(5)CO, respectively. These observed vibrational wavenumbers and relative IR intensities agree with those reported for C(6)H(5)CO isolated in solid Ar and with values predicted for C(6)H(5)CO with the B3LYP/aug-cc-pVDZ method. The rotational contours of the two bands near 1838 and 1131 cm(-1) simulated according to rotational parameters predicted with the B3LYP/aug-cc-pVDZ method fit satisfactorily with the experimental results. Additional products BrCO, C(6)H(5)C(O)Br, and C(6)H(5)C(O)C(6)H(5) were identified in the C(6)H(5)Br/CO/N(2) experiments; the kinetics involving C(6)H(5)CO and C(6)H(5)C(O)Br are discussed.     

Conformational equilibrium of bis(trifluoromethanesulfonyl) imide anion of a room-temperature ionic liquid: Raman spectroscopic study and DFT calculations

The structure of bis(trifluoromethanesulfonyl) imide (TFSI-) in the liquid state has been studied by means of Raman spectroscopy and DFT calculations. Raman spectra of 1-ethyl-3-methylimidazolium (EMI+) TFSI- show relatively strong bands arising from TFSI- at about 398 and 407 cm(-1). Interestingly, the 407 cm(-1) band, relative to the 398 cm(-1) one, is appreciably intensified with raising temperature, suggesting that an equilibrium is established between TFSI- conformers in the liquid state. According to DFT calculations followed by normal frequency analyses, two conformers of C2 and C1 symmetry, respectively, constitute global and local minima, with an energy difference 2.2-3.3 kJ mol(-1). The wagging omega-SO2 vibration appears at 396 and 430 cm(-1) for the C1 conformer and at 387 and 402 cm(-1) for the C2 one. Observed Raman spectra over the range 380-440 cm(-1) were deconvoluted to extract intrinsic bands of TFSI- conformers, and the enthalpy of conformational change from C2 to C1 was evaluated. The enthalpy value is in good agreement with that obtained by theoretical calculations. We thus conclude that a conformational equilibrium is established between the C1 and C2 conformers of TFSI- in the liquid EMI+TFSI-, and the C2 conformer is more favorable than the C1 one.     

Rearrangement of 3-deoxy-D-erythro-hexos-2-ulose in aqueous solution: NMR evidence of intramolecular 1,2-hydrogen transfer

Selective (13)C- and (2)H-labeling, and (13)C NMR spectroscopy, have been used to show that the 1,2-dicarbonyl compound (osone), 3-deoxy-D-erythro-hexos-2-ulose (3-deoxy-D-glucosone) (1; 3DG), degrades to 3-deoxy-D-ribo-hexonic acid 2 and 3-deoxy-D-arabino-hexonic acid 3 exclusively via an intramolecular 1,2-hydrogen transfer mechanism in aqueous phosphate buffer at pH 7.5 at 37 °C. Acids 2 and 3 are produced in significantly different amounts (1:6 ratio) despite the prochiral C3 in 1, and two potential reaction mechanisms are considered to explain the observed stereoselectivity. One mechanism involves acyclic forms of 1 as reactants, whereas the other assumes cyclic pyranose reactants. In the former (2-keto-hydrate or 2KH mechanism), putative transition state structures based on density functional theory (DFT) calculations arise from the C1 hydrate form of acyclic 1 having the C1-H1 bond roughly orthogonal to the C2 carbonyl plane. The relative orientation of the alkoxide oxygen atom at C1 and the C2 carbonyl oxygen, and H-bonding between C(1)OH and the C2 carbonyl oxygen, contribute to the stability of the transition state. DFT calculations of the natural charges on individual atoms in the transition state show the migrating hydrogen to have an almost neutral charge, implying that it may more closely resemble a hydrogen atom than a hydride anion during transfer from C1 to C2. A second mechanism (2-keto-pyranose or 2KP mechanism) involving the cyclic 2-keto-pyranoses of 1 as reactants aligns the C1-H1 bond orthogonal to the C2 carbonyl plane in different ring conformations of both anomers, with the β-pyranose giving 3 and the α-pyranose giving 2. While both the 2KH and 2KP mechanisms are possible, the latter readily leads to a prediction of the reaction stereospecificity that is consistent with the experimental data.     

纳米磷酸铁锂的制备及电化学性能研究

利用液相沉淀法合成了纳米级磷酸铁,并以此为铁源,通过碳热还原技术制备了粒径均匀的纳米级球形LiFePO4/C正极材料。经热分析(TG-DSC)、X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)以及恒电流充放电测试,研究了纳米磷酸铁及纳米磷酸铁锂材料的结构、形貌以及电化学性能。实验结果表明材料的首次放电比容量达161.8 mAh.g-1(0.1C),库仑效率为98.3%;室温下在0.2C、0.5C、1C、2C及5C倍率充放电其首次放电比容量分别为156.5、144、138.9、125.6和105.7 mAh·g-1,材料具有较好的倍率性能。