Stereoselective synthesis of the C-11 to C-19 segment of macrolactin 3 via a center inversion followed by Oxa-Michael addition approach

An efficient and short stereoselective synthesis of C11–C19 fragment of Macrolactin 3 was achieved. The vic-triol moiety (C15–C17) was derived from the C2–C4 chiral centers of D-mannose. The C-1 of D-mannose was utilized for the Wittig-olefination followed by hydroxylation using hydroboration reaction to introduce C11–C13 carbon chain in the C11–C19 fragment, whereas C5–C6 carbon chain of mannose was converted into C18–C19 of the target by dehydration reactions. Thus, the main strategy was (a) two consecutive Wittig-olefination reactions on C1 carbon of mannose, (b) inversion of C4 stereocenter, and (c) dehydration of C5–C6 vic-diol to olefin to result in the C11–C19 fragment.     

Organocatalyzed and Uncatalyzed CC/CC and CC/CN Exchange Processes between Knoevenagel and Imine Compounds in Dynamic Covalent Chemistry

Molecular diversity generation through reversible component exchange has acquired great importance in the last decade with the development of dynamic covalent chemistry. We explore here the recombination of components linked by C?C and C?N bonds through reversible double‐bond formation, and cleavage in C?C/C?C and C?C/C?N exchange processes. The reversibility of the Knoevenagel reaction has been explored, and C?C/C?C C/C exchanges have been achieved among different benzylidenes, under organocatalysis by secondary amines such as L ‐proline. The substituents of these benzylidenes were shown to play a very important role in the kinetics of the exchange reactions. L ‐Proline is also used to catalyze the reversible C?C/C?C exchange between Knoevenagel derivatives of barbituric acid and malononitrile. Finally, the interconversion between Knoevenagel derivatives of dimethylbarbituric acid and imines (C?C/C?N exchange) has been studied and was found to occur rapidly in the absence of catalyst. The results of this study pave the way for the extension of dynamic combinatorial chemistry based on C?C/C?C and C?C/C?N exchange systems.     

Group additive values for the gas phase standard enthalpy of formation of hydrocarbons and hydrocarbon radicals

A complete and consistent set of 95 Benson group additive values (GAV) for the standard enthalpy of formation of hydrocarbons and hydrocarbon radicals at 298 K and 1 bar is derived from an extensive and accurate database of 233 ab initio standard enthalpies of formation, calculated at the CBS-QB3 level of theory. The accuracy of the database was further improved by adding newly determined bond additive corrections (BAC) to the CBS-QB3 enthalpies. The mean absolute deviation (MAD) for a training set of 51 hydrocarbons is better than 2 kJ mol(-1). GAVs for 16 hydrocarbon groups, i.e., C(C(d))(3)(C), C-(C(d))(4), C-(C(t))(C(d))(C)(2), C-(C(t))(C(d))(2)(C), C-(C(t))(C(d))(3), C-(C(t))(2)(C)(2), C-(C(t))(2)(C(d))(C), C-(C(t))(2)(C(d))(2), C-(C(t))(3)(C), C-(C(t))(3)(C(d)), C-(C(t))(4), C-(C(b))(C(d))(C)(H), C-(C(b))(C(t))(H)(2), C-(C(b))(C(t))(C)(H), C-(C(b))(C(t))(C)(2), C(d)-(C(b))(C(t)), for 25 hydrocarbon radical groups, and several ring strain corrections (RSC) are determined for the first time. The new parameters significantly extend the applicability of Benson's group additivity method. The extensive database allowed an evaluation of previously proposed methods to account for non-next-nearest neighbor interactions (NNI). Here, a novel consistent scheme is proposed to account for NNIs in radicals. In addition, hydrogen bond increments (HBI) are determined for the calculation of radical standard enthalpies of formation. In particular for resonance stabilized radicals, the HBI method provides an improvement over Benson's group additivity method.     

Synthesis of the ABCD and ABCDE ring systems of azaspiracid-1

The efficient syntheses of the ABCD ring system of the originally proposed structure of azaspiracid-1 and the ABCDE ring system of the revised structure of azaspiracid-1 containing the correct stereochemistry at C(6), C(10), C(13), C(14), C(16), C(17), C(19), C(21), C(22), C(24) and C(25) have been achieved.     

Theoretical study of the stability of multiply charged C70 fullerenes

We have calculated the electronic energies and optimum geometries of C(70) (q+) and C(68) (q+) fullerenes (q=0-14) by means of density functional theory. The ionization energies for C(70) and C(68) fullerenes increase more or less linearly as functions of charge, consistent with the previously reported behavior for C(60) and C(58) [S. Diaz-Tendero et al., J. Chem. Phys. 123, 184306 (2005)]. The dissociation energies corresponding to the C(70) (q+)-->C(68) (q+)+C(2), C(70) (q+)-->C(68) ((q-1)+)+C(2) (+), C(70) (q+)-->C(68) ((q-2)+)+C(+)+C(+), C(70) (q+)-->C(68) ((q-3)+)+C(2+)+C(+), and C(70) (q+)-->C(68) ((q-4)+)+C(2+)+C(2+) decay channels show that C(70) (q+) (like C(60) (q+)) is thermodynamically unstable for q>or=6. However, the slope of the dissociation energy as a function of charge for a given decay channel is different from that of C(60) (q+) fullerenes. On the basis of these results, we predict q=17 to be the highest charge state for which a fission barrier exists for C(70) (q+).     

新一族疏水缔合聚丙烯酰胺NaAMC14S/AM与Gemini表面活性剂之间的相互作用

在水溶液中进行了表面活性单体丙烯酰胺基十四烷基磺酸钠(NaAMC14S)与丙烯酰胺(AM)的均相共聚合, 制备了具有微嵌段结构的疏水缔合聚丙烯酰胺NaAMC14S/AM, 合成了阳离子型Gemini表面活性剂二溴化-N,N′-二(二甲基十二烷基)己二铵(C12C6C12Br2), 采用表观粘度法和荧光探针法研究了共聚物NaAMC14S/AM与Gemini表面活性剂C12C6C12Br2的相互作用. 研究结果表明, 疏水缔合聚丙烯酰胺NaAMC14S/AM与Gemini表面活性剂C12C6C12Br2之间存在着很强的相互作用, 既存在静电相互作用, 又存在强烈的疏水相互作用, 表现在以下几方面: C12C6C12Br2的加入, 使共聚物NaAMC14S/AM在浓度小于其临界缔合浓度(cac)时即发生分子间的缔合; C12C6C12Br2在低于其临界胶束浓度时, 就与共聚物NaAMC14S/AM形成混合胶束; 当共聚物的浓度为0.30%(w)时, 随着C12C6C12Br2加入量的增多, 共聚物水溶液的粘度会发生大幅度的增加, 在最大值处粘度竟提高了3个数量级. 研究还发现, 共聚物NaAMC14S/AM与C12C6C12Br2之间的相互作用还与共聚物分子链中的疏水微嵌段含量有关, 疏水微嵌段含量越多, NaAMC14S/AM与C12C6C12Br2之间的相互作用越强, 溶液粘度增加的程度越大.     

Interactions of beta-lactoglobulin with sodium decylsulfonate, decyltriethylammonium bromide, and their mixtures

The interactions of beta-lactoglobulin (BLG) with anionic surfactant sodium decylsulfonate (C10SO3), cationic surfactant decyltriethylammonium bromide (C10NE), and the mixtures of cationic-anionic surfactants (C10NE-C10SO3) were investigated by circular dichroism (CD) and fluorescence methods. At pH 7.0, C10NE and the C10NE-rich surfactant mixtures of C10NE-C10SO3 could form precipitates with BLG, while C10SO3, equimolar mixtures of C10NE-C10SO3, or C10SO3-rich mixtures of C10NE-C10SO3 form homogeneous solutions with BLG. CD observed that both C10NE and C10SO3 could change the BLG structure. The effects of the mixtures of C10NE-C10SO3 on BLG structure depended on the ratio of C10NE to C10SO3. The C10NE-rich or the C10SO3-rich mixtures of C10NE-C10SO3 could significantly affect BLG structure, while the equimolar mixtures of C10NE-C10SO3 exhibited weaker interaction with BLG. Fluorescence measurements showed that both C10NE and C10SO3 could induce the enhancement of fluorescence of BLG, and C10NE enhanced the BLG fluorescence more than C10SO3 did. The effect of the mixtures of C10NE-C10SO3 on the fluorescence of BLG became stronger with the increase of the molar fraction of C10NE in C10NE-C10SO3 mixtures.     

Room-temperature phosphorescence and energy transfer in luminescent multinuclear platinum(II) complexes of branched alkynyls

A series of luminescent branched platinum(II) alkynyl complexes, [1,3,5-{RC[triple bond]C(PEt3)2PtC[triple bond]C-C6H4C[triple bond]C}3C6H3] (R=C6H5, C6H4OMe, C6H4Me, C6H4CF3, C5H4N, C6H4SAc, 1-napthyl (Np), 1-pyrenyl (Pyr), 1-anthryl-8-ethynyl (HC[triple bond]CAn)), [1,3-{PyrC[triple chemical bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-{(iPr)3SiC[triple bond]C}C6H3], and [1,3-{PyrC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-(HC[triple bond]C)C6H3], was successfully synthesized by using the precursors [1,3,5-{Cl(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] or [1,3-{Cl(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-{(iPr)3SiC[triple bond]C}C6H3]. The X-ray crystal structures of [1,3,5-{MeOC6H4C[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] and [1,8-{Cl(PEt3)2PtC[triple bond]C}2An] have been determined. These complexes were found to show long-lived emission in both solution and solid-state phases at room temperature. The emission origin of the branched complexes [1,3,5-{RC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] with R=C6H5, C6H4OMe, C6H4Me, C6H4CF3, C5H4N, and C6H4SAc was tentatively assigned to be derived from triplet states of predominantly intraligand (IL) character with some mixing of metal-to-ligand charge-transfer (MLCT) (dpi(Pt)-->pi*(C[triple bond]CR)) character, while the emission origin of the branched complexes with polyaromatic alkynyl ligands, [1,3,5-{RC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}3C6H3] with R=Np, Pyr, or HC[triple bond]CAn, [1,3-{PyrC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-{(iPr)3SiC[triple bond]C}C6H3], [1,3-{PyrC[triple bond]C(PEt3)2PtC[triple bond]CC6H4C[triple bond]C}2-5-(HC[triple bond]C)C6H3], and [1,8-{Cl(PEt3)2PtC[triple bond]C}2An], was tentatively assigned to be derived from the predominantly 3IL states of the respective polyaromatic alkynyl ligands, mixed with some 3MLCT (d(pi)(Pt)-->pi*(C[triple bond]CR)) character. By incorporating different alkynyl ligands into the periphery of these branched complexes, one could readily tune the nature of the lowest energy emissive state and the direction of the excitation energy transfer.     

金属碳笼(Met-Cars)化学反应的理论研究 2: Ti8C12与H2O,C2H4生成Ti8C12(H2O)8和Ti8C12(C2H4)4反应的ab initio研究

用量子化学从头计算方法, 研究了Ti8C12分别与H2O, C2H4作用形成Ti8C12(H2O)8, Ti8C12(C2H4)4的反应。计算结果表明, 在Ti8C12(H2O)8中, 电子由H2O向Ti8C12转移, 在Ti8C12(C2H4)4中, 电子由Ti8C12向C2H4转移。从Ti8C12生成Ti8C12(H2O)8能量降低, 稳定性增加, 生成Ti8C12(C2H4)4能量升高, 稳定性减小。     

Ruthenium(II)‐Catalyzed C−C Arylations and Alkylations: Decarbamoylative C−C Functionalizations

Ruthenium(II)biscarboxylate catalysis enabled selective C−C functionalizations by means of decarbamoylative C−C arylations. The versatility of the ruthenium(II) catalysis was reflected by widely applicable C−C arylations and C−C alkylations of aryl amides, as well as acids with modifiable pyrazoles, through facile organometallic C−C activation.     

Decompaction of cationic gemini surfactant-induced DNA condensates by beta-cyclodextrin or anionic surfactant

Compaction of DNA by cationic gemini surfactant hexamethylene-1,6-bis-(dodecyldimethylammoniumbromide) (C12C6C12Br2) and the subsequent decompaction of the DNA-C12C6C12Br2 complexes by beta-cyclodextrin (beta-CD) or sodium dodecyl sulfate (SDS) have been studied by using zeta potential and particle size measurements, atomic force microscopy (AFM), isothermal titration microcalorimetry (ITC), and circular dichroism. The results show that C12C6C12Br2 can induce the collapse of DNA into densely packed bead-like structures with smaller size in an all-or-none manner, accompanied by the increase of zeta potential from highly negative values to highly positive values. In the decompaction of the DNA-C12C6C12Br2 complexes, beta-CD and SDS exhibit different behaviors. For beta-CD, the experimental results suggest that it can remove the outlayer hydrophobically bound C12C6C12Br2 molecules from the DNA-C12C6C12Br2 complexes by inclusion interaction, and the excess beta-CD may attach on the complexes by forming inclusion complexes with the hydrocarbon chains of the electrostatically bound C12C6C12Br2 that cannot be removed. The increase of steric hindrance due to the attachment of beta-CD molecules results in the decompaction of the DNA condensates though the true release of DNA cannot be attained. However, for SDS, the experimental results suggest that it can realize the decompaction and release of DNA from its complexes with C12C6C12Br2 due to both ion-pairing and hydrophobic interaction between SDS and C12C6C12Br2.     

Structure, stability, and NMR properties of lower fullerenes C38-C50 and azafullerene C44N6

A systematic survey of the complete set of isomers of fullerenes C(38), C(40), C(42), C(44), C(46), C(48), C(50) and azafullerene C(44)N(6) is reported. All isomeric structures were optimized using first-principle density functional theory at the B3LYP/6-31G level. The isomeric structures with the lowest energies are C(38):17, C(40):38, C(42):45, C(44):75, C(44):89, C(46):109, C(48):171, and C(50):270. The ground-state structure of the azafullerene C(44)N(6) in the framework of C(50):270 has D(3) symmetry. The (13)C NMR chemical shifts and nucleus-independent chemical shifts (NICS) for the stable isomers of each fullerene are presented.     

Recent Advances in Radical‐Mediated C—C Bond Fragmentation of Non‐Strained Molecules

The carbon‐carbon (C—C) σ‐bonds construct the fundamental frameworks of organic molecules. The direct functionalization of C—C bonds represents one of the most efficient and step‐economical transformations in synthetic chemistry. The past few decades have witnessed the fast development of transition‐metal mediated C—C bond activation. In contrast, the radical‐promoted C—C bond cleavage has received relatively less attention. As the occurrence of ring strain significantly facilitates the fission of cyclic C—C bonds via radical approaches, the strain relief‐driven C—C bond activation mostly relies on the three‐ and four‐membered rings. The C—C activation of non‐strained molecules such as medium‐ or large‐sized rings and linear alkanes remains challenging. In this review, we will focus on the recent advances in radical‐mediated C—C bond activation of non‐strained molecules. Herein, the alkoxy‐ and iminyl‐radical triggered scission of non‐strained C—C bonds and C—C cleavage via the strategy of remote functional group migration is summarized.     

Cuprous Oxide Catalyzed Oxidative CC Bond Cleavage for CN Bond Formation: Synthesis of Cyclic Imides from Ketones and Amines

Selective oxidative cleavage of a C? C bond offers a straightforward method to functionalize organic skeletons. Reported herein is the oxidative C? C bond cleavage of ketone for C? N bond formation over a cuprous oxide catalyst with molecular oxygen as the oxidant. A wide range of ketones and amines are converted into cyclic imides with moderate to excellent yields. In‐depth studies show that both α‐C? H and β‐C? H bonds adjacent to the carbonyl groups are indispensable for the C? C bond cleavage. DFT calculations indicate the reaction is initiated with the oxidation of the α‐C? H bond. Amines lower the activation energy of the C? C bond cleavage, and thus promote the reaction. New insight into the C? C bond cleavage mechanism is presented.     

Composition and major odorous compounds of the essential oil of Bifora radians,an aldehyde-producing weed

The composition of the essential oil of Bifora radians, an aldehyde-producing weed, has been investigated by capillary gas chromatography, coupled gas chromatography – mass spectrometry, on-line catalytic hydrogenation and coupled gas chromatography – infrared spectrometry. The nineteen compounds identified included eighteen aldehydes: seven alkanals (C6, C9, C10, C11, C12, C13, and C14), ten alkenals, including five (E)-2-alkenals (C12, C13, C14, C15, and C16), and one (E,E)-2,4-alkadienal (C13). Typical Bifora odors were attributed to three major (E)-2-alkenals, C12, C13, and C14.     

Ruthenium-Catalyzed Activation of Nonpolar C−C Bonds via π-Coordination-Enabled Aromatization

Activation of C−C bonds allows editing of molecular skeletons, but methods for selective activation of nonpolar C−C bonds in the absence of a chelation effect or a driving force derived from opening of a strained ring are scarce. Herein, we report a method for ruthenium-catalyzed activation of nonpolar C−C bonds of pro-aromatic compounds by means of π-coordination-enabled aromatization. This method was effective for cleavage of C−C(alkyl) and C−C(aryl) bonds and for ring-opening of spirocyclic compounds, providing an array of benzene-ring-containing products. The isolation of a methyl ruthenium complex intermediate supports a mechanism involving ruthenium-mediated C−C bond cleavage.     

Reactions of fullerenes with reactive methylene organophosphorus reagents: efficient synthesis of organophosphorus group substituted C60 and C70 derivatives

Treatment of C70 with cycloalkylaminomethylenebisphosphonates in the presence of NaH gave corresponding C70 dimers 1 in good yield, while the methanofullerenes, C70>CH(PO3Et2) (3) and C70>C(PO3Et2)2 (4) or C60>CH(PO3Et2) (5) and C60>C(PO3Et2)2 (6), were obtained, respectively, by the reaction of C70 or C60 with tetraethyl methylenediphosphonate in the presence of NaH. Diethyl cyanomethylphosphonate reacted with C60 or C70 under similar conditions to afford C60>C(PO3Et2)CN (7) and C70>C(PO3Et2)CN (8). Furthermore, the presence of weak electronic interactions between two fullerene cages of fullerene dimers was demonstrated by cyclic voltammetry. A radical mechanism was proposed for the formation of the fullerene derivatives on the basis of the ESR studies.     

诺卜醇衍生物的合成及其13C化学位移分析

诺卜基醚;诺卜基酯;诺卜醇衍生物的合成及其13C化学位移分析     

Synthesis and X-ray or NMR/DFT structure elucidation of twenty-one new trifluoromethyl derivatives of soluble cage isomers of C76, C78, C84, and C90

Adding 1% of the metallic elements cerium, lanthanum, and yttrium to graphite rod electrodes resulted in different amounts of the hollow higher fullerenes (HHFs) C76-D2(1), C78-C2v(2), and C78-C2v(3) in carbon-arc fullerene-containing soots. The reaction of trifluoroiodomethane with these and other soluble HHFs at 520-550 degrees C produced 21 new C76,78,84,90(CF3)n derivatives (n = 6, 8, 10, 12, 14). The reaction with C76-D2(1) produced an abundant isomer of C2-(C76-D2(1))(CF3)10 plus smaller amounts of an isomer of C1-(C76-D2(1))(CF3)6, two isomers of C1-(C76-D2(1))(CF3)8, four isomers of C1-(C76-D2(1))(CF3)10, and one isomer of C2-(C76-D2(1))(CF3)12. The reaction with a mixture of C78-D3(1), C78-C2v(2), and C78-C2v(3) produced the previously reported isomer C1-(C78-C2v(3))(CF3)12 (characterized by X-ray crystallography in this work) and the following new compounds: C2-(C78-C2v(3))(CF3)8; C2-(C78-D3(1))(CF3)10 and C(s)-(C78-C2v(2))(CF3)10 (both characterized by X-ray crystallography in this work); C2-(C78-C2v(2))(CF3)10; and C1-C78(CF3)14 (cage isomer unknown). The reaction of a mixture of soluble higher fullerenes including C84 and C90 produced the new compounds C1-C84(CF3)10 (cage isomer unknown), C1-(C84-C2(11))(CF3)12 (X-ray structure reported recently), D2-(C84-D2(22))(CF3)12, C2-(C84-D2(22))(CF3)12, C1-C84(CF3)14 (cage isomer unknown), C1-(C90-C1(32))(CF3)12, and another isomer of C1-C90(CF3)12 (cage isomer unknown). All compounds were studied by mass spectrometry, (19)F NMR spectroscopy, and DFT calculations. An analysis of the addition patterns of these compounds and three other HHF(X) n compounds with bulky X groups has led to the discovery of the following addition-pattern principle for HHFs: In general, the most pyramidal cage C(sp(2)) atoms in the parent HHF, which form the most electron-rich and therefore the most reactive cage C-C bonds as far as 1,2-additions are concerned, are not the cage C atoms to which bulky substituents are added. Instead, ribbons of edge-sharing p-C6(X)2 hexagons, with X groups on less pyramidal cage C atoms, are formed, and the otherwise "most reactive" fullerene double bonds remain intact.     

Cuprous Oxide Catalyzed Oxidative C?C Bond Cleavage for C?N Bond Formation: Synthesis of Cyclic Imides from Ketones and Amines

Selective oxidative cleavage of a C C bond offers a straightforward method to functionalize organic skeletons. Reported herein is the oxidative C C bond cleavage of ketone for C N bond formation over a cuprous oxide catalyst with molecular oxygen as the oxidant. A wide range of ketones and amines are converted into cyclic imides with moderate to excellent yields. In‐depth studies show that both α‐C H and β‐C H bonds adjacent to the carbonyl groups are indispensable for the C C bond cleavage. DFT calculations indicate the reaction is initiated with the oxidation of the α‐C H bond. Amines lower the activation energy of the C C bond cleavage, and thus promote the reaction. New insight into the C C bond cleavage mechanism is presented.