氧化硅负载的固体碱上乙醛的气相缩合反应

在氧化硅负载的含碱金属固体碱催化剂上乙醛能有效地缩合生成丁烯醛及丁烯醇,反应具有中等转化率、较好的选择性(约90％)和稳定性.考察了不同反应条件对催化性能的影响,并对可能的反应活性相进行了探讨.     

Solid‐Phase Synthesis of 2‐Alkenamides from Polystyrene‐Supported α‐Selenocarboxylic Acids

The polystyrene‐supported α‐selenoacetic acid and α‐selenopropionic acid were prepared and used for the synthesis of 2‐alkenamides from primary and secondary amines in good yields and high purities.     

Solid‐State Synthesis and Characterization of 2‐Thioxo‐4‐Imidazolidinone Derivatives

A new and efficient two‐step solid‐state synthesis method is described for 2‐thioxo‐4‐imidazolidinone from aryl isothiocyanate and free amino acid. This method requires only simple equipment and is easy to perform. The products reported were characterized on the basis of IR, MS, ¹H NMR, ¹³C NMR and elemental analysis.     

A Facile Solid‐Phase Synthesis of (+)‐(S)‐Clopidogrel

Enantiomerically pure (+)‐(S)‐clopidogrel was prepared by solid‐phase synthesis using the commercially available Wang resin. This method offers mild reaction conditions and provides the (+)‐(S)‐clopidogrel in overall 52% yield over six steps and with optical purity of 98.0% ee.     

Voltammetric Determination of Surface‐Confined Biomolecules with N‐(2‐Ethyl‐ferrocene)maleimide

A thiol‐specific electroactive cross‐linker, N‐(2‐ethyl‐ferrocene)maleimide (Fc‐Mi), has been used to tag surface‐confined peptides containing cysteine residues or oligodeoxynucleotides (ODNs) whose 3′ ends have been modified with thiol groups. The peptides studied herein include both the oxidized and reduced forms of glutathione and a hexapeptide. Cyclic voltammograms (CVs) of the Fc‐Mi groups attached to the surfaces were used to quantify the total number of cysteine residues that are tagged and/or can undergo facile electron transfer reactions with the underlying electrodes. A quartz crystal microbalance was used in conjunction with CV to estimate the total number of cysteine groups labeled by Fc‐Mi per peptide molecule. By comparing to mass spectrometric studies, it is confirmed that not all of the Fc‐Mi linked to the cysteine groups can participate in the electron transfer reactions. The methodology is further extended to the determination of ODN samples in a sandwich assay wherein the thiol linker on the 3′ end can be tagged with Fc‐Mi. The analytical performance was evaluated through determinations of a complementary ODN target and targets with varying numbers of mismatching bases. ODN samples as low as 10 fmol can be detected. Such a low detection level is remarkable considering that no signal amplification scheme is involved in the current method. The approach is shown to be sequence‐ and/or structure‐specific and does not require sophisticated instrumentation and complex experimental procedure.     

Atom transfer radical polymerization of n‐butyl acrylate catalyzed by CuBr/N‐(n‐hexyl)‐2‐pyridylmethanimine

The homogeneous atom transfer radical polymerization (ATRP) of n‐butyl acrylate with CuBr/N‐(n‐hexyl)‐2‐pyridylmethanimine as a catalyst and ethyl 2‐bromoisobutyrate as an initiator was investigated. The kinetic plots of ln([M]₀/[M]) versus the reaction time for the ATRP systems in different solvents such as toluene, anisole, N,N‐dimethylformamide, and 1‐butanol were linear throughout the reactions, and the experimental molecular weights increased linearly with increasing monomer conversion and were very close to the theoretical values. These, together with the relatively narrow molecular weight distributions (polydispersity index ～ 1.40 in most cases with monomer conversion > 50%), indicated that the polymerization was living and controlled. Toluene appeared to be the best solvent for the studied ATRP system in terms of the polymerization rate and molecular weight distribution among the solvents used. The polymerization showed zero order with respect to both the initiator and the catalyst, probably because of the presence of a self‐regulation process at the beginning of the reaction. The reaction temperature had a positive effect on the polymerization rate, and the optimum reaction temperature was found to be 100 °C. An apparent enthalpy of activation of 81.2 kJ/mol was determined for the ATRP of n‐butyl acrylate, corresponding to an enthalpy of equilibrium of 63.6 kJ/mol. An apparent enthalpy of activation of 52.8 kJ/mol was also obtained for the ATRP of methyl methacrylate under similar reaction conditions. Moreover, the CuBr/N‐(n‐hexyl)‐2‐pyridylmethanimine‐based system was proven to be applicable to living block copolymerization and living random copolymerization of n‐butyl acrylate with methyl methacrylate. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3549–3561, 2002     

Formation of Dimers of Some 2‐Substituted Indan‐1‐one Derivatives during Base‐Mediated Cross‐Aldol Condensation

Unexpected dimers of some 2‐substituted indan‐1‐one derivatives were isolated during aldol condensation of indan‐1‐one with various aldehydes in the presence of KOH (see Scheme). Monomeric products, usually expected from aldol condensation, further underwent a base‐catalyzed nucleophilic addition reaction to their dimeric form in some cases. The structures of these dimers were characterized by using various spectral techniques and in one case, structural details were determined from a high‐resolution crystallographic analysis.     

Two Coordination Polymers based on 2‐Ethyl‐1H‐imidazole‐4,5‐dicarboxylic Acid and 1,3‐Bis(4‐pyridyl)propane: Synthesis,Crystal Structures,and Photoluminescent Properties

Two coordination polymers, [Cd(Heidc)(bpp)]_n ( 1 ) and [Zn₃ (eidc)₂(bpp)(H₂O)₂] · 2H₂O}_n ( 2 ) (H₃eidc = 2‐ethyl‐4,5‐imidazole dicarboxylic acid, bpp = 1,3‐bis(4‐pyridyl)propane) were hydrothermally synthesized and characterized by elemental analysis, IR, spectroscopy single‐crystal X‐ray diffraction, and thermogravimetric analyses. Compound 1 features a 2D layer formed by C–H ··· π stacking interactions between adjacent chains, whereas compound 2 shows a 3D (8³)₂(8⁵.10)‐tfc framework constructed of the 2D (6,3) layer. The result demonstrates that the central metal atoms play a key role in governing the coordination motifs. Moreover, solid‐state properties such as thermal stabilities and photoluminescence of 1 and 2 were also investigated.     

Continuous Dehydrogenation of n‐Pentanol over a Cr Modified Cu/γ‐Al2O3‐La2O3 Catalyst

The oxidant‐free dehydrogenation of n‐pentanol over copper based catalysts was investigated in this paper. The effect of metal modification on the activity and stability of the copper catalyst supported on γ‐Al₂O₃ and La₂O₃ (Cu/γ‐Al₂O₃‐La₂O₃) was clarified and a Cr modified Cu/Al₂O₃‐La₂O₃ (Cu‐Cr/γ‐Al₂O₃‐La₂O₃) showed the best catalytic performance. The conversion of n‐pentanol was 70.0% and the selectivity for n‐pentanal increased to 97.1% over Cu‐Cr/γ‐Al₂O₃‐La₂O₃. X‐ray diffraction and temperature programmed reduction of H₂ indicated that the addition of Cr favors the formation and reduction of the copper oxide, and the dispersion of the active Cu⁰ species, accounting for the good activity and stability of this catalyst. Furthermore, the lower amount of acidic sites in Cu‐Cr/γ‐Al₂O₃‐La₂O₃ is suggested to suppress the dehydration in oxidant‐free dehydrogenation of n‐pentanol, accounting for the higher selectivity for n‐pentanal.     

Investigation of catalyst‐transfer condensation polymerization for the synthesis of n‐type π‐conjugated polymer,poly(2‐dioxaalkylpyridine‐3,6‐diyl)

Kumada‐Tamao coupling polymerization of 6‐bromo‐3‐chloromagnesio‐2‐(3‐(2‐methoxyethoxy)propyl)pyridine 1 with a Ni catalyst and Suzuki‐Miyaura coupling polymerization of boronic ester monomer 2 , which has the same substituted pyridine structure, with ^tBu₃PPd(o‐tolyl)Br were investigated for the synthesis of a well‐defined n‐type π‐conjugated polymer. We first carried out a model reaction of 2,5‐dibromopyridine with 0.5 equivalent of phenylmagnesium chloride in the presence of Ni(dppp)Cl₂ and then observed exclusive formation of 2,5‐diphenylpyridine, indicating that successive coupling reaction took place via intramolecular transfer of Ni(0) catalyst on the pyridine ring. Then, we examined the Kumada‐Tamao polymerization of 1 and found that it proceeded homogeneously to afford soluble, regioregular head‐to‐tail poly(pyridine‐2,5‐diyl), poly(3‐(2‐(2‐(methoxyethoxy)propyl)pyridine) (PMEPPy). However, the molecular weight distribution of the polymers obtained with several Ni and Pd catalysts was very broad, and the matrix‐assisted laser desorption ionization time‐of‐flight mass spectra showed that the polymer had Br/Br and Br/H end groups, implying that the catalyst‐transfer polymerization is accompanied with disproportionation. Suzuki‐Miyaura polymerization of 2 with ^tBu₃PPd(o‐tolyl)Br also afforded PMEPPy with a broad molecular weight distribution, and the tolyl/tolyl‐ended polymer was a major product, again indicating the occurrence of disproportionation. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Catalytic Oxidation of Methane to C2‐C4 Hydrocarbons over CeO2 Promoted W‐Mn/SiO2 Catalysts at Higher Pressure

CeO₂‐promoted Na‐Mn‐W/SiO₂ catalyst has been studied for catalytic oxidation of methane in a micro‐stainless‐steel reactor at elevated pressure. The effect of operating conditions, such as GHSV, pressure and CH₄/O₂ ratio, has been investigated. 22.0% CH₄ conversion with 73.8% C₂‐C₄ selectivity (C₂/C₃/C₄ = 3.8/1.0/3.6) was obtained at 1003 K, 1.5 × 10⁵ h^?;1 GHSV and 1.0 MPa. The results show: Elevated pressure disadvantages the catalytic oxidation of methane to C₂‐C₄ hydrocarbons. Large amounts of C₃ and C₄ hydrocarbons are observed. The unfavorable effects of elevated pressure can be overcome by increasing GHSV; the reaction is strongly dependent on the operating conditions at elevated pressure, particularly dependent on GHSV and ratio of CH₄/O₂. Analyses by means of XRD, XPS and CO₂‐TPD show that CO₂ produced from the reaction makes a weakly poisoning capacity of the catalyst; information of changeful valence on Ce and Mn was detected over the near‐surface of the Ce‐Na‐W‐Mn/SiO₂ catalyst; the existence of Ce³⁺/Ce⁴⁺ and Mn²⁺/Mn³⁺ ion couple supported that the reaction over the catalyst followed the Redeal‐Redox mechanism. Oxidative re‐coupling of C₂H₆ and CH₄ in gas phase or over surface of catalyst produces C₃ or C₄ hydrocarbons.     

Synthesis and characterization of di‐n‐butyltin(IV) complexes with 4′/2′‐nitrobiphenyl‐2‐carboxylic acids: X‐ray crystal structures of [{(n‐C4H9)2Sn(OCOC12H8NO2−4′)}2O]2 and (n‐C4H9)2Sn{OCOC12H8NO2−4′}2

Reactions of di‐n‐butyltin(IV) oxide with 4′/2′‐nitrobiphenyl‐2‐carboxylic acids in 1 : 1 and 1 : 2 stoichiometry yield complexes [{(n‐C₄H₉)₂Sn(OCOC₁₂H₈NO₂?4′/2′)}₂O]₂ ( 1 and 2 ) and (n‐C₄H₉)₂Sn(OCOC₁₂H₈NO₂?4′/2′)₂ ( 3 and 4 ) respectively. These compounds were characterized by elemental analysis, IR and NMR (¹H, ¹³C and ¹¹⁹Sn) spectroscopy. The IR spectra of these compounds indicate the presence of anisobidentate carboxylate groups and non‐linear C? Sn? C bonds. From the chemical shifts δ (¹¹⁹Sn) and the coupling constants ¹J(¹³C, ¹¹⁹Sn), the coordination number of the tin atom and the geometry of its coordination sphere have been suggested. [{(n‐C₄H₉)₂Sn(OCOC₁₂H₈NO₂?4′)}₂O]₂ ( 1 ) exhibits a dimeric structure containing distannoxane units with two types of tin atom with essentially identical geometry. To a first approximation, the tin atoms appear to be pentacoordinated with distorted trigonal bipyramidal geometry. However, each type of tin atom is further subjected to a sixth weaker interaction and may be described as having a capped trigonal bipyramidal structure. The diffraction study of the complex (n‐C₄H₉)₂Sn(OCOC₁₂H₈NO₂?4′)₂ ( 3 ) shows a six–coordinate tin in a distorted octahedral frame containing bidentate asymmetric chelating carboxylate groups, with the n‐Bu groups trans to each other. The n‐Bu? Sn? n‐Bu angle is 152.8° and the Sn? O distances are 2.108(4) and 2.493(5) Å. The oxygen atom of the nitro group of the ligand does not participate in bonding to the tin atom in 1 and 3 . Crystals of 1 are triclinic with space group P1 and of that of 3 have orthorhombic space group Pnna. Copyright © 2003 John Wiley & Sons, Ltd.     

Lewis Acids as Mild and Effective Catalysts for the Synthesis of 3,5‐Bis[(hetero)arylidene]piperidin‐4‐ones

The aldol‐crotonic condensation reactions of N‐alkyl‐ and NH‐piperidin‐4‐one derivatives with (hetero)aromatic aldehydes promoted by Lewis acids or bases were examined. This comparative study has revealed three effective catalytic systems based on Lewis acids, i.e., LiClO₄ and MgBr₂ (in the presence of tertiary amine), and BF₃⋅Et₂O, for the synthesis of N‐alkyl‐substituted 3,5‐bis(heteroarylidene)piperidin‐4‐ones, including those bearing acid‐ or base‐labile groups both in the (hetero)aromatic groups and in the alkyl substituent at the N‐atom. The highest reaction rate was observed for LiClO₄‐mediated synthesis. Both MgBr₂‐ and LiClO₄‐mediated syntheses were inefficient in the case of NH‐piperidin‐4‐one, while BF₃⋅Et₂O provided the final compounds in high yields. This catalyst is especially advantageous as it allows simultaneous condensation and deprotection in the case of O‐protected piperidin‐4‐one.     

Preparation of Some Novel,Highly Unstable Chain Conjugated 2H‐Pyran‐5‐carboxylates

Aldol condensations of conjugated unsaturated β‐ketoesters and unsaturated aldehydes gave chain conjugated 2H‐pyran‐5‐carboxylates.     

Preparation of the β2‐Homoselenocysteine Derivatives Fmoc‐(S)‐β2hSec(PMB)‐OH and Boc‐(S)‐β2hSec(PMB)‐OH for Solution and Solid‐Phase Peptide Synthesis

Fmoc‐β²hSer(^tBu)‐OH was converted to Fmoc‐β²hSec(PMB)‐OH in five steps. To avoid elimination of HSeR, the selenyl group was introduced in the second last step (Fmoc‐β²hSer(Ts)‐OAll→Fmoc‐β²hSec(PMB)‐OAll). In a similar way, the N‐Boc‐protected compound was prepared. With the β²hSe‐derivatives, 21 β²‐amino‐acid building blocks with proteinogenic side chains are now available for peptide synthesis.     

固相β-环糊精包结物诱导7-羟基-2-甲氧基-2-甲基色满的不对称合成

研究了室温下间苯二酚和甲基乙烯基酮分别与β-环糊精（ β-CD）形成包结物后的几种不同固相反应,结果表明包结物A（间苯二酚/β-CD）与包结物B（甲基乙烯基酮/β-CD）反应能够很好地得到目的产物,产率及ee值分别为82.8%和78.4%;间苯二酚与包结物B反应仅得到低光学活性产物（ee值为19.5%）;包结物A与甲基乙烯基酮反应却没有得到手性目的产物。以熔点、X-粉末衍射、固相核磁碳谱及ROESY多种方法对所形成的包结物进行了表征,包结物中主客体的比例（1：1）通过¹H NMR (400 MHz)得以确定,文章对固相环加成反应的机制也进行了初步探讨。     

Embryotoxicity studies of tri‐n‐butyltin(IV) complexes of 5‐[(E)‐2‐(aryl)‐1‐diazenyl]‐2‐hydroxybenzoic acid and 2‐[(E)‐2‐(3‐formyl‐4‐hydroxyphenyl)‐1‐diazenyl] benzoic acid on sea urchin development

The toxicity studies of free 5‐[(E)‐2‐(aryl)‐1‐diazenyl]‐2‐hydroxybenzoic acid and 2‐[(E)‐2‐(3‐formyl‐4‐hydroxyphenyl)‐1‐diazenyl]benzoic acid and their tri‐n‐butyltin(IV) complexes were evaluated by using sea urchin early developmental stages as recommended model organisms for toxicity tests. The novel complexes, as the parent tri‐n‐butyltin(IV) chloride (TBTCl), caused mitosis block and induced high embryonic mortality in sea urchin. Copyright © 2005 John Wiley & Sons, Ltd.     

Facile Solid‐Phase Organic Synthesis of 5‐Vinyl‐Substituted 1,2,4‐Oxadiazoles from Polymer‐Bound α‐Selenopropionic Acid

Cyclocondensation of polystyrene‐supported α‐selenopropionic acid with amidoximes in the presence of 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride (EDC) followed by oxidative deselenation efficiently afforded 5‐vinyl 1,2,4‐oxadiazoles in good yield and purity with a facile work‐up procedure.     

Liquid Phase Hydrogenolysis of Biomass‐derived Lactate to 1,2‐Propanediol over Silica Supported Cobalt Nanocatalyst

Liquid phase hydrogenolysis of ethyl lactate to 1,2‐propanediol was performed over silica supporting cobalt catalysts prepared by two different methods: precipitation‐gel (PG) technique and deposition‐precipitation (DP) procedure. The cobalt species (Co₃O₄/cobalt phyllosilicate) present in the corresponding calcined PG and DP catalysts were different as a consequence of the preparation methods, and Co OH Co olation and Si O Co oxolation molecular mechanisms were employed to elucidate the chemical phenomena during the different preparation procedures. In addition, the texture (BET), reduction behavior (TPR and in‐situ XRD), surface dispersion and state of cobalt species (XPS), and catalytic performance differ greatly between the samples. Because of small particle size, high dispersion of cobalt species and facile reducibility, the Co/SiO₂ catalyst prepared by precipitation‐gel method presented a much higher activity than the catalyst prepared by deposition‐precipitation method. Metallic cobalt is assumed to be the catalytically active site for the hydrogenolysis reaction according to the catalytic results of both cobalt samples reduced at different temperatures and the structure changes after reaction.     

Dehydrogenation of Isobutane to Isobutene with Carbon Dioxide over SBA‐15‐Supported Chromia‐Ceria Catalysts

A series of SBA‐15‐supported chromia‐ceria catalysts with 3% Cr and 1%–5% Ce (3Cr‐Ce/SBA) were prepared using an incipient wetness impregnation method. The catalysts were characterized by XRD, N₂ adsorption, SEM, TEM‐EDX, Raman spectroscopy, UV–vis spectroscopy, XPS and H₂‐TPR, and their catalytic performance for isobutane dehydrogenation with CO₂ was tested. The addition of ceria to SBA‐15‐supported chromia improves the dispersion of chromium species. 3Cr‐Ce/SBA catalysts are more active than SBA‐15‐supported chromia (3Cr/SBA), which is due to a higher concentration of Cr⁶⁺ species present on the former catalysts. The 3Cr‐3Ce/SBA catalyst shows the highest activity, which gives 35.4% isobutane conversion and 89.6% isobutene selectivity at 570 °C after 10 min of the reaction.