Feigrisolide C: structural revision and synthesis

[Carbohydrate structure: see text] The original macrodiolide structure proposed for feigrisolide C was incorrect. The true structure of feigrisolide C was identified as (2'S,3'S,6'R,8'R)-homononactoyl (2R,3R,6S,8S)-nonactic acid, which was confirmed by total synthesis.     

Stereoselective synthesis of the published structure of feigrisolide A. Structural revision of feigrisolides A and B

The total synthesis of the proposed structure of feigrisolide A is reported. Ethyl (S)-3-hydroxybutyrate was the chiral starting material. A Brown asymmetric allylation and an Evans aldol reaction were key steps of the synthesis. The NMR data of the synthetic product are different from those of the natural product. The published structure of feigrisolide A is therefore erroneous. A subsequent comparison of spectral data strongly suggests that feigrisolides A and B are identical with (-)-nonactic acid and (+)-homononactic acid, respectively.     

Dynamics of the F atom reaction with propene

The F+C2H3CH3 reaction has been investigated using the crossed molecular beam technique. Three reaction channels have been observed in this reaction: H+C3H5F, CH3+C2H3F, and HF+C3H5. Time-of-flight spectra as well as product laboratory angular distributions have been measured for the HF, C2H3F, and C3H5F products from these three channels. Relative branching ratios of the three observed reaction channels have also been estimated. Experimental results indicate that these different channels exhibit significantly different reaction dynamics.     

Mechanochemical Reactions of Fullerenes under High-Speed Vibration Milling

Since a novel technique called "high-speed vibration milling" (HSVM) was first applied to the Reformatskytype reaction of C60 in 1996, [1] this technique has been applied to various kinds of fullerene functionalizations including the preparation of C120. [2] Most recent reactions of fullerenes under HSVM conditions will be discussed: (1)reaction of C60/C70 with N-alkylglycines and aldehydes (Scheme 1); (2) reaction of C60 with active methylene compounds in the presence of bases (Scheme 2); (3) reaction of C6o with diazo compounds (Scheme 3); (4) reaction of C6o with anthracene derivatives (Scheme 4).     

气相反应C_(60)+O_3=C_(6O)(C_(2v))+O_2热力学函数的计算

计算了气相反应C60＋O3＝C6O（C2v）＋O2的热力学函数．得到了该反应Gibbs自由能的具体数值，结果表明在所研究的温度范围内Gibbs自由能为负值，从热力学角度来说，该反应可以自发进行,在计算该气相反应热力学函数的基础上，给出了气相C6O（C2v）的标准热力学函数     

Reaction of levoglucosenone with diazocyclopropane

Depending of the reaction conditions, reaction of levoglucosenone with diazocyclopropane generated in situ from N-cyclopropyl- N-nitrosourea under the action of bases involved either the carbonyl group to give oxaspiropentane (MeONa/MeOH, s-30 °C), or the double C=C bond to give l-pyrazoline (K2CO3, CH2Cl2, 5 °C). The latter readily reacted with diazocyclopropane at the C=O group or added as a C-nucleophile in a regio-and stereoselective Michael reaction to the C=C bond of levoglucosenone. The direction of reaction depended on the reactant ratio. The reaction of the levoglucosenone—diazomethane adduct with an excess of levoglucosenone in the presence of a base yielded similar product bearing two levoglucosenone moieties.     

固相反应法制备Pt-Ru/C催化剂对乙醇氧化的电催化活性研究

0引言近年来,直接甲醇燃料电池(DMFC)由于其燃料来源丰富、价格低廉、甲醇携带和储存安全方便等独特的优越性而越来越受到重视[1]。但是甲醇具有一定的毒性,因此要想实现DMFC在诸如手机、笔记本电脑以及电动车等可移动电源领域的应用,必须探索新的液体燃料以替代有毒性的甲醇。     

A Single‐Molecule‐Level Mechanistic Study of Pd‐Catalyzed and Cu‐Catalyzed Homocoupling of Aryl Bromide on an Au(111) Surface

On‐surface Pd‐ and Cu‐catalyzed C?C coupling reactions between phenyl bromide functionalized porphyrin derivatives on an Au(111) surface have been investigated under ultra‐high vacuum conditions by using scanning tunneling microscopy and kinetic Monte Carlo simulations. We monitored the isothermal reaction kinetics by allowing the reaction to proceed at different temperatures. We discovered that the reactions catalyzed by Pd or Cu can be described as a two‐phase process that involves an initial activation followed by C?C bond formation. However, the distinctive reaction kinetics and the C?C bond‐formation yield associated with the two catalysts account for the different reaction mechanisms: the initial activation phase is the rate‐limiting step for the Cu‐catalyzed reaction at all temperatures tested, whereas the later phase of C?C formation is the rate‐limiting step for the Pd‐catalyzed reaction at high temperature. Analysis of rate constants of the Pd‐catalyzed reactions allowed us to determine its activation energy as (0.41±0.03) eV.     

Mechanism and kinetics of the atmospheric degradation of perfluoropolymethylisopropyl ether by OH radical: a theoretical study

In the present work, the mechanism and kinetics of the reaction of perfluoropolymethylisopropyl ether (PFPMIE) with OH radical are studied. The reaction between PFPMIE and OH radical is initiated through breaking of C–C or C–O bond of PFPMIE. These reactions lead to the formation of COF₂ molecules and alkyl radical. The pathways corresponding to the reaction between PFPMIE and OH radical have been modelled using density functional theory methods M06-2X and MPW1K with 6-31G(d,p) basis set. It is found that the C–C bond breaking reaction is most favourable than the C–O bond breaking reaction. The subsequent reactions of the alkyl radicals, formed from the C–C bond breaking reactions, are studied in detail. The rate constant for the initial oxidation reactions is calculated using canonical variational transition state theory with small curvature tunnelling corrections over the temperature range of 278–350 K. From the calculated reaction, potential energy surface and rate constant, the lifetime and global warming potential of PFPMIE are studied.     

Effect of the reaction temperature on the transglycosylation reactions catalyzed by the cyclodextrin glucanotransferase from Bacillus macerans for the synthesis of large-ring cyclodextrins

The synthesis of cyclodextrins with from 6 to more than 50 glucose units by cyclodextrin glucanotransferase (CGTase, EC 2.4.1.19) from Bacillus macerans was investigated. Analysis of the synthesized cyclic α-1,4-glucan products showed that a higher yield of large-ring cyclodextrins were obtained with a reaction temperature of 60 °C compared to 40 °C. The yield of large-ring cyclodextrins obtained at 60 °C represented about 50% of the total glucans employed in the reaction. Analysis of the cyclodextrin-forming cyclization reaction and of the coupling reaction of the CGTase resulting in the degradation of mainly the larger cyclic α-1,4-glucans indicated higher rates of the cyclization reaction at 60 °C compared to 40 °C while the opposite was found for the coupling reaction.     

Preparation of Pt／C Catalyst with Solid Phase Reaction Method

The Pt/C catalyst was prepared with solid phase reaction method (Pt/C(S)) for the first time.Its Performances were compared with that prepared by the traditional liquid phase reaction method. The results demonstrate that the electrocatalytic activity of Pt/C catalyst with solid phase reaction method for methanol oxidation is higher than that with liquid phase reaction method. XRD and TEM measurements indicate that the Pt/C(S) possesses low crystalline extent and small particle size.     

An MEDT study of the mechanism and selectivities of the [3+2] cycloaddition reaction of tomentosin with benzonitrile oxide

The [3+2] cycloaddition (32CA) reaction of tomentosin with benzonitrile oxide yielding a spiro-isoxazoline has been studied within the Molecular Electron Density Theory at the B3LYP/6-31(d,p) computational level. Given the multifunctionality of tomentosin, this 32CA reaction can take place along 16 competitive reaction paths. The chemo-, regio-, and stereoisomeric reaction paths involving the two C C double bonds of tomentosin have been studied. Density functional theory (DFT) calculations account for the total chemo- and regioselectivity, in complete agreement with the experimental outcomes, being suggestive of low diastereofacial selectivity. Analysis of the conceptual DFT indices accounts for the nonpolar character of this 32CA reaction. On the other hand, the topological analysis of the electron localization function of the selected points of the intrinsic reaction coordinate associated with the formation of the C C and C O single bonds emphasizes the zw-type reactivity of the phenyl nitrile oxide; the reaction taking place through a non-concerted two-stage one-step mechanism initialized with the formation of the C C single bond involving the β-conjugated carbon of tomentosin.     

Towards Stereoselective Synthesis of the C(31)–C(39) and C(20)–C(27) Fragments of Phorboxazole A

The stereoselective synthesis of the C(31)–C(39) and C(20)–C(27) fragments of phorboxazole A ( 1 ) was achieved from commercially available and inexpensive D ‐mannitol. Crimmins aldol reaction and a decarboxylative Claisen‐type reaction are the key steps for the C(31)–C(39) fragment, and L ‐proline‐catalyzed aldol reaction, Sharpless asymmetric epoxidation, and epoxide ring opening reaction with Gilman's reagent are the key steps for the C(20)–C(27) fragment of phorboxazole.     

Catalytic reactions of C4 hydrocarbons on the fluid catalytic cracking catalyst

利用小型固定流化床实验装置,对C4烃类在催化裂化催化剂上催化转化反应规律进行了实验研究,考察了不同反应温度及空速对C4烃类催化转化反应的产物分布和组成的影响。实验结果表明,催化裂化催化剂对C4烃类具有一定芳构化和裂化性能,在适宜的反应条件下,可增产芳烃和丙烯;在C4烃类催化转化过程中,丁烯是主要的反应物,而丁烷几乎不反应;低反应温度有利于增产芳烃,高反应温度有利于增产丙烯。较低的空速对增产芳烃和丙烯都有利。根据双分子反应机理和反应结果,建立了C4烃类在催化裂化催化剂上催化转化过程的反应网络。对C4烃类催化转化历程分析表明,中间产物碳五和碳六烯烃较弱的二次裂化性能是C4烃类在催化裂化催化剂上催化转化过程中乙烯和丙烯产率较低的主要原因。     

Highly regio- and stereoselective synthesis of 2(E),4-Alkadienoates via the Pd(0)-catalyzed reaction of aryl halides with 3,4-alkadienoates

[reaction: see text] 2(E),4-Alkadienoates were prepared highly stereoselectively via the Pd(0)/Ag(2)CO(3)-cocatalyzed reaction of 3,4-alkadienoates and aryl halides. The reaction is believed to proceed via the oxidative addition-carbopalladation-beta-H elimination process. Compared to the other reported methods for the synthesis of 2,4-alkadienoates, in which usually only disubstituted C=C bonds were formed, the current reaction forms the trisubstituted or even tetrasubstituted C=C bond highly stereoselectively.     

C−C Bond Formation of Benzyl Alcohols and Alkynes Using a Catalytic Amount of KOtBu: Unusual Regioselectivity through a Radical Mechanism

We report a C?C bond‐forming reaction between benzyl alcohols and alkynes in the presence of a catalytic amount of KO^tBu to form α‐alkylated ketones in which the C=O group is located on the side derived from the alcohol. The reaction proceeds under thermal conditions (125 °C) and produces no waste, making the reaction highly atom efficient, environmentally benign, and sustainable. Based on our mechanistic investigations, we propose that the reaction proceeds through radical pathways.     

Gold‐Catalyzed Formal C−C Bond Insertion Reaction of 2‐Aryl‐2‐diazoesters with 1,3‐Diketones

The transition‐metal‐catalyzed formal C−C bond insertion reaction of diazo compounds with monocarbonyl compounds is well established, but the related reaction of 1,3‐diketones instead gives C−H bond insertion products. Herein, we report a protocol for a gold‐catalyzed formal C−C bond insertion reaction of 2‐aryl‐2‐diazoesters with 1,3‐diketones, which provides efficient access to polycarbonyl compounds with an all‐carbon quaternary center. The aryl ester moiety plays a crucial role in the unusual chemoselectivity, and the addition of a Brønsted acid to the reaction mixture improves the yield of the C−C bond insertion product. A reaction mechanism involving cyclopropanation of a gold carbenoid with an enolate and ring‐opening of the resulting donor–acceptor‐type cyclopropane intermediate is proposed. This mechanism differs from that of the traditional Lewis‐acid‐catalyzed C−C bond insertion reaction of diazo compounds with monocarbonyl compounds, which involves a rearrangement of a zwitterion intermediate as a key step.     

氯取代丙烷伯氢反应的准经典轨线研究

用准经典轨线方法研究了氯取代丙烷伯氢的反应.采用三体LEPS势能函数构筑势能面.结果表明, 氯取代丙烷伯氢的反应呈现出与氯取代丙烷仲氢反应不同的微观反应进程.对于氯取代丙烷仲氢的反应,只有一种反应通道,反应过程中有碰撞复合物产生.对于氯取代丙烷伯氢的反应,有两种反应通道,一种有碰撞复合物生成,另一种则没有.     

Total synthesis of ingenol

Total synthesis of ingenol, a diterpene isolated from the genus Euphorbia, was accomplished on the basis of the novel key reactions. The highly strained ingenane skeleton was constructed through an intramolecular cyclization reaction of an acetylene dicobalt complex followed by a rearrangement reaction of an epoxy alcohol. The C(3),C(4),C(5)-triol moiety was introduced by a stereoselective double dihydroxylation reaction of a diene having C(2)-C(3) and C(4)-C(5) double bonds.     

An improved understanding of the reaction of bis(bromomethyl)quinoxaline 1-N-oxides with amines using substituent effects

The reaction of bis(bromomethyl)quinoxaline N-oxides with amines is interesting from a reaction mechanism perspective and due to the reported biological activity of compounds in this general class. The complex mechanism of this reaction (particularly in the case of primary amines) is complicated further when C6 or C7 substituted mono-N-oxides are considered. In this study, the synthesis and subsequent characterization of a series of 2,3-bis(bromomethyl)quinoxaline 1-N-oxides is reported. Experimental and computational evidence is used to show that the observed product ratios from the reaction with diethylamine reflect the influence of both the C6/C7 substituent and the N-oxide functional group on the initial nucleophilic substitution reaction.