Concise total syntheses of (±)isopaucifloral F, (±)quadrangularin A, and (±)pallidol

Concise total syntheses of (±)isopaucifloral F, (±)quadrangularin A, and (±)pallidol, starting from commercially available 3,5-dimethoxybenzoic acid, have been achieved by a sequential process. The overall synthetic strategy involves Nazarov cyclization, Ramberg-Backlund olefination, and Friedel-Crafts alkylation.     

Sulfoxide‐Based Enantioselective Nazarov Cyclization: Divergent Syntheses of (+)‐Isopaucifloral F, (+)‐Quadrangularin A,and (+)‐Pallidol

The synthesis of enantiomerically pure 3‐aryl substituted indanones is developed using an enantioselective sulfoxide‐based Knoevenagel condensation/Nazarov cyclization procedure. After the reductive desulfonation of the methyl para‐tolyl sulfoxide‐containing chiral auxiliary under mild conditions, selected enantiomerically pure indanone is used for the divergent total syntheses of three resveratrol natural products (+)‐isopaucifloral F, (+)‐quadrangularin A, and (+)‐pallidol.     

Total synthesis of norleucosceptroids F and G

First total synthesis of norleucosceptroids F and G has been achieved through key steps of Michael–Aldol cascade, oxa-Michael cyclization–dehydration–deprotection cascade and cross metathesis(CM), this work developed a general and concise method to the synthesis of leucosceptroid and norleucosceptroid.     

An efficient synthesis of the 1,6-dioxaspiro[4.4]nonan-2-one motif of the immunosuppressive triterpenoid Phainanoid F

We describe an efficient synthesis of the 1,6-dioxaspiro[4.4]nonan-2-one motif of the immunosuppressive triterpenoid Phainanoid F and its C4 epimer. A furan oxidative spirocyclization for constructing the spiro center was used as the key step. Other important reactions involved Sharpless asymmetric dihydroxylation, Weinreb ketone synthesis and Yamaguchi esterfication. The synthesis was achieved in 11 linear steps with 17.3% overall yield.     

Brønsted acid promoted intramolecular cyclization of O-alkynyl benzoic acids: Concise total synthesis of exserolide F

Herein we report the stereoselective total synthesis of Exserolide F. The key step involves triflic acid catalyzed highly regioselective intramolecular cyclization of an O-alkynyl benzoic acid derivative to accomplish the core isocoumarin skeleton of the natural product via 6-endo-dig mode of cyclization. The other important steps are: Sharpless asymmetric epoxidation, Barbier propargylation, Sonogashira coupling en route to access the O-alkynyl benzoic acid derivative.     

嫁接Al改性MCM-41介孔分子筛催化合成双酚F

以十六烷基三甲基溴化铵和正硅酸乙酯为原料,合成纯硅MCM-41介孔分子筛。 再利用九水硝酸铝为改性剂来嫁接改性纯硅MCM-41介孔分子筛,NH3-TPD结果表明,嫁接后的AlMCM-41产生了中强酸。 用改性后不同n(Si)/n(Al)的AlMCM-41催化合成双酚F,在n（苯酚）/n（甲醛）=30、反应时间5 h、反应温度90 ℃、m（甲醛）/m（AlMCM-41）=7的反应条件下,在一定范围内,双酚F的产率随Al含量增加而增加,但在n（Si）/n（Al）＜50时,双酚F的产率反而下降,当n（Si）/n（Al）=50时,双酚F的产率最高,为42.28%。     

The Structure of Taiwanin F from Taiwania Cryptomerioides Hayata

Reinvestigation of the nonvolatile fraction of the acetone extractive from the heartwood of Taiwania cryptomerioides Hayata afforded taiwanin F which was established as 11-hydroxy-7-oxohinokiol on the basis of spectral data and its synthesis from hinokiol. In addition, six known compounds, taiwanin A, savinin, taiwanin C, hinokiol, taiwanin E and diphyllin were also isolated from the same fraction.     

加速器质谱测量用NH4Hf2F9的制备及表征

研究了加速器质谱测量用NH4Hf2F9的制备方法,用XRD,SEM,XPS和TG-DTA表征其结构和组成.结果表明:NH4Hf2F9样品在573 K热处理1 h后物相并未变化,而在773,973,1173,1373 K热处理1 h后物相则都转变为HfO2.TG-DTA的分析表明从573 K开始NH4Hf2F9样品逐渐开始分解,至1073 K时失重约78%.样品微观形貌为不规则的固体颗粒,颗粒的粒径分布较大,范围在5～20μm之间.粉末样品主要含有Hf,N和F元素,其中Hf主要以(+4)价存在.     

Towards Nonalternant Nanographenes through Self-Promoted Intramolecular Indenoannulation Cascade by C−F Bond Activation

Large polycyclic aromatic hydrocarbons (PAHs) containing pentagons represent an important class of compounds that are considered to be superior materials in future nano-electronic applications. From this perspective, the development of synthetic approaches to large PAHs and nanographenes (NGs) is a matter of great importance. In this context indenoannulation appears to be the most practical way to introduce pentagons into NGs. Here we report that alumina-mediated C−F bond activation is an attractive tool for the synthesis of non-alternant NGs bearing several pentagons. The unique nature of the reaction leads to a rather counter-intuitive outcome and allows considering each previous aryl–aryl coupling as a promoter of the following one, despite the continuous increase in the strain energy. Thus, the presented strategy combines both facile synthesis and significant yields for large nonalternant PAHs and NGs.     

Indium-Catalyzed C−F Bond Transformation through Oxymetalation/β-Fluorine Elimination to Access Fluorinated Isocoumarins

Fluorinated heterocycles have attracted much attention in the pharmaceutical and agrochemical industries. Many strategies have already been developed to achieve the synthesis of fluorinated heterocycles. Formidable challenges remain, however, in the synthesis of fluorinated isocoumarin derivatives that are among the most alluring structural motifs. Herein, the indium-catalyzed C−F bond transformation of 2-(2,2-difluorovinyl) benzoates is reported, which are readily accessible compounds, to give a diverse array of fluorinated isocoumarins. The present reaction proceeds smoothly using inexpensive reagents: a catalytic amount of indium salt in the presence of zinc salt. A theoretical calculation of potential energy profiles showed that the reaction consists of oxymetalation with the elimination of alkyl halide and the β-fluorine elimination.     

[F]Fluoromethyl iodide ([F]FCH2I): preparation and reactions with phenol, thiophenol, amide and amine functional groups

In this study, we report the synthesis and reactivity of [¹⁸F]fluoromethyl iodide ([¹⁸F]FCH₂I) with various nucleophilic substrates and the stabilities of [¹⁸F]fluoromethylated compounds. [¹⁸F]FCH₂I was prepared by reacting diiodomethane (CH₂I₂) with [¹⁸F]KF, and purified by distillation in radiochemical yields of 14-31% (n = 25). [¹⁸F]FCH₂I was stable in organic solvents commonly used for labeling and aqueous solution with pH 1-7, but was unstable in basic solutions. [¹⁸F]FCH₂I displayed a high reactivity with various nucleophilic substrates such as phenol, thiophenol, amide and amine. The [¹⁸F]fluoromethylated compounds synthesized by the reactions of phenol, thiophenol and tertiary amine with [¹⁸F]FCH₂I were stable for purification, formulation and storage. In contrast, the [¹⁸F]fluoromethylated compounds synthesized by the reactions of primary or secondary amines, and amide with [¹⁸F]FCH₂I were too unstable to be detected or purified from the reaction mixtures. Defluorination of these [¹⁸F]fluoromethyl compounds was a main decomposition route.     

F NMR applications in chemical biology

Although fluorine plays only a minor role in biology, its physicochemical properties have proven incredibly useful in the design of analogues of biologically important molecules. Analysis of organofluorine compounds by ¹⁹F NMR was largely confined to synthetic chemists but this technique is finding increasing applications in biological systems. The fluorine atom with its relative small size and 100% natural isotope abundance represents an attractive option for biological NMR studies. In this paper we review the recent literature highlighting the exploitation of ¹⁹F NMR in a range of research areas at the interface of chemistry and biology.     

Boron-Centered Lewis Superacid through Redox-Active Ligands: Application in C−F and S−F Bond Activation

A series of redox-responsive ferrocenyl-substituted boranes and boronic esters were synthesized. Oxidation of the ferrocenyl ligand to the ferrocenium resulted in a drastic increase in the Lewis acidity beyond the strength of SbF₅, which was investigated experimentally and computationally. The resulting highly Lewis acidic boron compounds were used for catalytic C−F and S−F bond activation.     

Improving the accuracy of 1H–19F internuclear distance measurement using 2D 1H–19F HOESY

With the rise in fluorinated pharmaceuticals, it is becoming increasingly important to develop new ¹⁹F NMR-based methods to assist in their analysis. Crucially, obtaining information regarding the conformational dynamics of a molecule in solution can aid the design of strongly binding therapeutics. Herein, we report the development of a 2D ¹H–¹⁹F Heteronuclear Overhauser Spectroscopy (HOESY) experiment to measure ¹H–¹⁹F internuclear distances, with accuracies of ~5% when compared with ¹H–¹⁹F internuclear distances calculated by quantum chemical methods. We demonstrate that correcting for cross-relaxation of ¹H, using the diagonal peaks from the 2D ¹H–¹H Nuclear Overhauser Enhancement Spectroscopy (NOESY), is critical in obtaining accurate values for ¹H–¹⁹F internuclear distances. Finally, we show that by using the proposed method to measure ¹H–¹⁹F internuclear distances, we are able to determine the relative stereochemistry of two fluorinated pharmaceuticals.     

Temperature Dependence in the Synthesis of SBA-16-Type Mesoporous Silica with Pluronic F68 Block Copolymer

By adjusting the local effective surfactant packing parameter through synthesis temperature, highly ordered SBA-16-type mesoporous silica materials have been synthesized by templating with a nonionic triblock copolymer Pluronic F68 in strongly acidic conditions at temperature 30～40°C with the addition of K₂SO₄. The prepared SBA-16-type mesoporous silica materials having Im3m cubic mesostructure were proved by the well-defined x-ray diffraction patterns combined with transmission electron microscopy. Scanning electron microscopy indicated that a transformation from faced-sphere to faced-polyhedron shape morphologies could be induced with increasing of the synthesis temperature. The nitrogen adsorption–desorption analysis revealed that the mean pore size (5.50～6.13 nm) of the prepared materials increased with increasing synthesis temperature. However, when the synthesis temperature exceeded 46°C, only disordered mesoporous silca was obtained. Our synthesis strategies by adjusting the local effective surfactant packing parameter through synthesis condition, even in a narrow range, would be used not only to optimize the synthesis conditions of reported mesoporous silca, but also to fabricate new mesoporous silica materials with well-ordered channel and anticipated morphologies.     

Tl系列超导体中掺F研究

Ｔｌ系列超导体中掺Ｆ研究周鼎元（上海闸北教育学院，上海２０００７０）徐昌华（上海工业大学，上海２０００７２）陈敏（上海市长城电子工业公司，上海）关键词％Ｔｌ系超导体，掺Ｆ在ＲＢａ。Ｃｕ。Ｏｘ中掺加Ｆ的研究已有不少报逍（”．本文研究在ＴＩ系列超导体中掺...     

Monofluoroalkene-Isostere as a 19F NMR Label for the Peptide Backbone: Synthesis and Evaluation in Membrane-Bound PGLa and (KIGAKI)3

Solid-state ¹⁹F NMR is a powerful method to study the interactions of biologically active peptides with membranes. So far, in labelled peptides, the ¹⁹F-reporter group has always been installed on the side chain of an amino acid. Given the fact that monofluoroalkenes are non-hydrolyzable peptide bond mimics, we have synthesized a monofluoroalkene-based dipeptide isostere, Val-Ψ[(Z)-CF=CH]-Gly, and inserted it in the sequence of two well-studied antimicrobial peptides: PGLa and (KIGAKI)₃ are representatives of an α-helix and a β-sheet. The conformations and biological activities of these labeled peptides were studied to assess the suitability of monofluoroalkenes for ¹⁹F NMR structure analysis.     

Gaseous reaction mechanism of C2F radical with water

The kinetic properties of the carbon-fluorine radicals are little understood except those of CFn (n =1-3). In this article, a detailed mechanistic study was reported on the gas-phase reaction between the simplest pi-bonded C2F radical and water as the first attempt to understand the chemical reactivity of the C2F radical. Various reaction channels are considered. The most kinetically competitive channel is the quasi-direct hydrogen-abstraction route forming P5 HCCF + OH. At the CCSD(T)/6-311+G(2d,2p)//B3LYP/6-311G(d,p)+ZPVE, CCSD(T)/6-311+G(3df,2p)//QCISD/6-311G(d,p)+ZPVE and Gaussian-3//B3LYP/6-31G(d) levels, the overall H-abstraction barriers (4.5, 4.7, and 4.2 kcal/mol) for the C2F + H2O reaction are comparable to the corresponding values (5.5, 3.7, and 5.7 kcal/mol) for the analogous C2H + H2O reaction. This suggests that C2F is a reactive radical like the extensively studied C2H, in contrast to the situation of the CF and CF2 radicals that have much lower reactivity than the corresponding hydrocarbon species. Thus, the C2F radical is expected to play an important role in the combustion processes of the carbon-fluorine chemistry. Furthermore, addition of a second H2O can catalyze the reaction with the H-abstraction barrier significantly reduced to a marginally zero value (0.5 kcal/mol). This is also indicative of the potential relevance of the title reactions in the low-temperature atmospheric chemistry.     

Synthesis of Diverse Aromatic Ketones through C−F Cleavage of Trifluoromethyl Group

An efficient synthetic method of aromatic ketones through C−F cleavage of trifluoromethyl group is disclosed. The high functional group tolerance of the transformation and the remarkable stability of trifluoromethyl group in various reactions enabled multi-substituted aromatic ketone synthesis in an efficient route involving useful transformations such as ortho-lithiation, aryne chemistry, and cross-couplings.