Dipole interaction-controlled stereoselectivity in aldol reaction of alpha-CF3 enolate with fluoral

The stereoselectivity of a reaction is generally determined by minimizing steric repulsion. However, the aldol reaction of alpha-CF(3)-ketone (Z)-enolate with fluoral anomalously gave an anti-aldol through a sterically demanding transition state, because of the strong dipole interaction of the two CF(3) groups. We have thus disclosed a paradigm shift from steric to electronic control of reaction stereoselectivity. [reaction: see text]     

A concise total synthesis of (-)-cylindricine C through a stereoselective intramolecular aza-[3 + 3] annulation strategy

[reaction: see text] An enantioselective total synthesis of (-)-cylindricine C is described, featuring a diastereoselective intramolecular aza-[3 + 3] annulation strategy and an interesting halohydrin formation of the C4-5 olefin for construction of C4-ketone. This work provides a unique approach to this family of natural products.     

Mercury(II) complex of inverted N-methylated porphyrin: HgPh(2-NCH3NCTPP)

The reaction of PhHgOAc with 2-NCH₃NCTPPH (2) gave a mercury(II) complex of (phenylato)(2-N-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′,N″)-mercury(II), [HgPh(2-NCH₃NCTPP); 7]; the coordination sphere around Hg(1) in 7 was a four-coordinate derivative with a seesaw geometry and dipole–dipole (DD) interaction governed the longitudinal relaxation rate for Hg(1)–Ph–H_2,6 protons of 7 in CDCl₃ (0.01 M) at 599.95 MHz.     

13β-乙基-3-甲氧基-甾-1,3,5(10),9(11)-四烯-17β-醇的间氯过氧苯甲酸氧化反应

研究了13β-乙基-3-甲氧基-甾-1,3,5(10),9(11)-四烯-17β-醇与间氯过氧苯甲酸的氧化反应, 得到了9β-羟基-11酮化合物和一个未知化合物9α-过氧甲氧基-11-酮化合物。推测了反应机理, 讨论了未知物的化学结构和构型。     

Novel mixed-valence manganese cluster with two distinct Mn3(II/III/II) and Mn3(III/II/III) trinuclear units in a pseudocubane-like arrangement

The reaction between Mn(ClO 4) 2 and di-(2-pyridyl)-ketone in the presence of the sodium salt of propanediol as a base in MeOH leads to the formation of a hexanuclear manganese cluster. This cluster has been characterized by the formula [Mn(II) 3Mn(III) 3O(OH)(CH 3pdol) 3(Hpdol) 3(pdol)](ClO 4) 4 ( 1). Molecular conductance measurements of a 10 (-3) M solution of compound 1 in CH 3CN, DMSO, or DMF give Lambda m = 529, 135, or 245 muS/cm, respectively, which suggests a 1:4 cation/anion electrolyte. The crystal structure of hexanuclear manganese cluster 1 consists of two distinct trinuclear units with a pseudocubane-like arrangement. The trinuclear units show two different valence distributions, Mn(II)/Mn(III)/Mn(II) and Mn(III)/Mn(II)/Mn(III). Additional features of interest for the compound include the fact that (a) two of the Mn(III) ions show a Jahn-Teller elongation, whereas the third ion shows a Jahn-Teller compression; (b) one bridge between Mn(III) atoms is an oxo (O (2-)) ion, whereas the bridge between Mn(II) and Mn(III) is a hydroxyl (OH (-)) group; and (c) the di-(2-pyridyl)-ketone ligand that is methanolyzed to methyl-Hpdol and R 2pdol (R = CH 3, H) acts in three different modes: methyl-pdol(-1), Hpdol(-1), and pdol(-2). For magnetic behavior, the general Hamiltonian formalism considers that (a) all of the interactions inside the two "cubanes" between Mn(II) and Mn(III) ions are equal to the J 1 constant, those between Mn(II) ions are equal to the J 2 constant, and those between the Mn(III) ions are equal to the J 3 constant and (b) the interaction between the two cubanes is equal to the J 4 constant. The fitting results are J 1 = J 2 = 0.7 cm (-1), J 3 approximately 0.0, J 4 = -6.2 cm (-1), and g = 2.0 (fixed). According to these results, the ground state is S = 1/2, and the next excited states are S = 3/2 and 5/2 at 0.7 and 1.8 cm (-1), respectively. The EPR spectra prove that the spin ground state at a low temperature is not purely S = 1/2 but is populated with the S = 3/2 state, which is in accordance with the susceptibility and magnetization measurements.     

Direct determination of the permanent dipole moments and structures of Al-CH(3)CN and Al-NH(3) by using a 2-m electrostatic hexapole field.

The supersonic beams of the (1-1) metal-ligand complexes of Al-CH(3)CN and Al-NH(3) were produced by a laser evaporation method. Nondestructive structure selection of the complexes and the dipole moment determination were performed by using a 2-m electrostatic hexapole field. The experimentally determined permanent dipole moments are 1.2 +/- 0.1 D for Al-CH(3)CN and 2.7 +/- 0.2 D for Al-NH(3). We find that the dipole moment of Al-NH(3) becomes larger than that of neat NH(3), while the formation of the Al-CH(3)CN complex produces a smaller dipole moment than that of neat CH(3)CN on the other hand. We performed the ab initio calculations to draw out plausible complex structures and to clarify the bonding character after formation of the complex, and we made comparisons with the computational results done by several groups. The Mulliken population analysis suggests the Al-->CH(3)CN charge flow, but on the other hand the Natural population analysis indicates very little charge flow. For the Al-NH(3) complex, the polarization effect of NH(3) and the N-->Al sigma donation would enhance the dipole moment strength. However, there still remains a controversial disagreement between the theoretical predictions and the experimental results. Further experimental determination using the hexapole method for various metal-ligand complexes and clusters could reveal the basic nature of interaction in the complex systems in general, and this method would complement theoretical calculations.     

Intensities of infrared bands in molecular mechanics (MM3)

The MM3 molecular mechanics program calculates a fair representation of vibrational frequencies for molecules. To make this information more useful, a qualitative intensity calculation has been added, as is described herein. Because each bond in the molecule is assigned a dipole moment, and the vibrational amplitudes are known from the frequency calculation, the change in dipole moment corresponding to each normal mode is readily calculated. In some cases a charge flux has to be added empirically for bond stretchings. This relatively simple calculation has been applied to a number of different functional groups, and gives band intensities adequate for dividing the bands into very strong, strong, medium, weak, or very weak (forbidden) categories. © 1992 by John Wiley & Sons, Inc.     

Experimental studies of light-induced charge transfer and charge redistribution in (X(2)-bipyridine)Re(I)(CO)(3)Cl complexes

Stark emission spectroscopy, transient DC photoconductivity (TDCP), and ground-state dipole moment measurements have been used to evaluate charge transfer (CT) within various (X(2)-bipyridine)Re(I)(CO)(3)Cl complexes following (3)MLCT excited-state formation. The Stark technique reports on vector differences between ground-state (mu(g)) and excited-state (mu(e)) dipole moments, while TDCP, when combined with independently obtained mu(g) information, reports on scalar differences. For systems featuring collinear, same-signed ground- and excited-state dipole moments, the scalar and vector differences are equivalent. However, for the low symmetry systems studied here, they are distinctly different. The vector difference yields the effective adiabatic one-electron-transfer distance (R(12)), while the combined vector and scalar data yield information about dipole rotation upon ground-state/excited-state interconversion. For the systems examined, charge transfer distances are substantially smaller than geometric electron-donor/electron-acceptor site separation distances. The measured distances are significantly affected by changes in acceptor ligand substituent composition. Electron-donating substituents decrease CT distances, while electron-withdrawing substituents increase CT distances, as do aromatic substituents that are capable of expanding the bipyridyl ligand (acceptor ligand) pi system. The Stark measurements additionally indicate that the CT vector and the transition dipole moment are significantly orthogonal, a consequence of strong polarization of the Re-Cl bond (orthogonal to the metal/acceptor-ligand plane) in the ground electronic state and relaxation of the polarization in the upper state. The ground-state Re-Cl bond polarization is sufficiently large that the overall ground-state scalar dipole moment exceeds the overall excited-state scalar dipole moment, despite transfer of an electron from the metal center to the diimine ligand. This finding provides an explanation for the otherwise puzzling negative solvatochromism exhibited in this family of compounds. Combining TDCP and Stark results, we find that the dipole moment can be rotated in some instances by more than 90 degrees upon (3)MLCT excited-state formation. The degree of rotation or reorientation can be modulated by changing the identity of the acceptor ligand substituents. Reorientational effects are smallest when the compounds feature aromatic substituents capable of spatially extending the pi system of the acceptor ligand.     

Synthesis of [3,4-(13)c(2)]-enriched bile salts as NMR probes of protein-ligand interactions

Synthetic methodology that allows for incorporation of isotopic carbon at the C-3 and C-4 positions of bile salts is reported. Three [3,4-(13)C(2)]-enriched bile salts were synthesized from either deoxycholic or lithocholic acid. The steroid 3alpha-OH group was oxidized and the A-ring was converted into the Delta(4)-3-ketone. The C-24 carboxylic acid was next converted into the carbonate group and selectively reduced to the alcohol in the presence of the A-ring enone. Following protection of the 24-OH group, the Delta(4)-3-ketone was converted into the A-ring enol lactone. Condensation of the enol lactone with [1,2-(13)C(2)]-enriched acetyl chloride and subsequent Robinson annulation afforded a [3,4-(13)C(2)]-enriched Delta(4)-3-ketone that was subsequently converted back into a 3alpha-hydroxy-5beta-reduced bile steroid. C-7 hydroxylation, when necessary, was achieved via conversion of the Delta(4)-3-ketone into the corresponding Delta(4,6)-dien-3-one, epoxidation of the Delta(6)-double bond, and hydrogenolysis/hydrogenation of the 5,6-epoxy enone system. The [3,4-(13)C(2)]-enriched bile salts were subsequently complexed to human ileal bile acid binding protein (I-BABP), and (1)H-(13)C HSQC spectra were recorded to show the utility of the compounds for investigating the interactions of bile acids with I-BABP.     

几种姜黄素类1,4-戊二烯-3-酮衍生物的合成及结构表征

以芳香醛和酮为原料,合成了3类姜黄素类1,5-二芳基-1,4-戊二烯-3-酮衍生物:1,5-二噻吩基-1,4-戊二烯-3-酮(Ⅰ)、1,5-二苯基-1,4-戊二烯-3-酮类(Ⅱ)和1,5-二呋喃基-1,4-戊二烯-3-酮(Ⅲ);利用元素分析、红外光谱、核磁共振谱(1 H NMR及13 C NMR)分析了产物的组成和结构,初步探讨了其反应条件和反应机理.结果表明,以无水乙醇为溶剂、8%的NaOH溶液为催化剂,反应温度为30⁵0℃时,反应产率较高.     

Annulation reactions of allene-derived 1,3-dipole with 3-substituted-chromones: unusual recognition of 4pi-component in 3-(N-Aryliminomethyl)chromones through

All-carbon dipole derived by the interaction of triphenylphosphine with allenic ester is able to locate the polarized 2pi-component in 3-formylchromones through a regioselective [2 + 3] addition to the C2-C3 pi-bond, which is followed by deformylation leading to novel 3a,9a-dihydro-1-ethoxycarbonyl-1-cyclopenteno[5, 4-b]benzopyran-4-ones. On the contrary, the dipole recognizes azadiene in 3-(N-aryliminomethyl)chromones through [4 + 3] annulation and initially formed adducts undergo tandem rearrangements to afford novel N-aryl-2, 3-dihydro-4-ethoxycarbonylchromano[2,3-b]azepine-6-ones in good yield.     

Synthesis of (24R)-3β-chloro-7α-bromo-5-hydroxy-5α-stigmastan-6-one and study of its dehydrohalogenation products

Starting from β-cytosterol (1) and going through the intermediate 3β-chloro-5α-hydroxy-6-ketone (2), the 3β-chloro-7α-bromo-5α-hydroxy-6-ketone (3) is synthesized. Dehydrohalogenation of3 in DMF in the presence of lithium carbonate and bromide gives the 6-ketosteroids4–6, depending on the reaction conditions. Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, 220141, Belarus, Minsk, ul. Akad. Kuprevicha, 5/2. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 617–622, September–October, 1999.     

Surface dipoles and work functions of alkylthiolates and fluorinated alkylthiolates on Au(111)

We study the dipole formation at the surface formed by -CH(3) and -CF(3) terminated short-chain alkylthiolate monolayers on Au(111). In particular, we monitor the change in work function upon chemisorption using density functional theory calculations. We separate the surface dipole into two contributions, resulting from the gold-adsorbate interaction and the intrinsic dipole of the adsorbate layer, respectively. The two contributions turn out to be approximately additive. Adsorbate dipoles are defined by calculating dipole densities of free-standing molecular monolayers. The gold-adsorbate interaction is, to a good degree, determined by the Au-S bond only. This bond is nearly apolar and its contribution to the surface dipole is relatively small. The surface dipole of the self-assembled monolayer is then dominated by the intrinsic dipole of the thiolate molecules. Alkylthiolates increase the work function of Au(111), whereas fluorinated alkylthiolates decrease it.     

Viscoelastic properties of poly(methyl methacrylate) with high glass transition temperature by lithium salt addition

The effect of ion‐dipole interaction between lithium cations and oxygen atoms in poly(methyl methacrylate) (PMMA), which leads to the great enhancement of glass transition temperature (T_g), on the linear viscoelastic properties is studied using binary blends of PMMA and lithium trifluoromethanesulfonate (LiCF₃SO₃). The strong interaction at low temperature leads to the high modulus in the glassy region even near T_g. The interaction becomes weak as increasing the temperature. Consequently, the rheological terminal region is clearly detected without a marked enhancement of steady‐state compliance, although the zero‐shear viscosity increases by the LiCF₃SO₃ addition. The result indicates that the crosslinking due to the ion‐dipole interaction has a lifetime that decides the longest relaxation time. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2388–2394     

A time-dependent density functional theory investigation on the nature of the electronic transitions involved in the nonlinear optical response of [Ru(CF3CO2)3T] (T = 4'-(C6H4-p-NBu2)-2,2':6',2'-terpyridine)

We report a theoretical study based on density functional theory (DFT) and time-dependent DFT (TDDFT) calculations on the nature and role of the absorption bands involved in the nonlinear optical response of the complexes [Ru(CF3CO2)3T] (T = T1, T2; T1 = 4'-(C6H4-p-NBu2)-2,2':6',2'-terpyridine, T2 = 4'-(C6H4-p-NMe2)-2,2':6',2'-terpyridine). Geometry optimizations, performed without any symmetry constraints, confirm a twisting of the -C6H4-p-NBu2 moiety with respect to the plane of the chelated terpyridine. Despite this lack of strong pi interaction, TDDFT excited states calculations of the electronic spectrum in solution provide evidence of a relevant role of the NBu2 donor group in the low-energy LMCT band at 911 nm. Calculations also show that the two bands at higher energy (508 and 455 nm) are not attributable only to LMCT and ILCT transitions but to a mixing of ILCT/MLCT and ILCT/pi-pi* transitions, respectively. The 911 nm LMCT band, appearing at lower wavelength of the second harmonic (670 nm) of the EFISH experiment, controls the negative value of the second-order NLO response. This is confirmed by our calculations of the static component beta0(zzz) of the quadratic hyperpolarizability tensor, showing a large positive value. In addition we have found that the increase of the dipole moment upon excitation occurs, in all the characterized transitions, along the dipole moment axis, thus explaining why the EFISH and solvatochromic experimental values of the quadratic hyperpolarizability agree as sign and value.     

1-甲基-3,4-二苯基喹啉-2(1H)-酮的合成和结构表征

以N-甲基苯胺和苯丙炔酸为原料,经过缩合、亲电环化、偶联反应合成了1-甲基-3,4-二苯基喹啉-2(1H)-酮;利用核磁共振谱和气相色谱-质谱表征了产物的结构.结果表明,所用合成方法具有产率高、反应条件温和、操作简单等优点,目标产物的总产率达62.7%.     

Reactions of CH3SH and (CH3)2S2 on the (0001) and (000) Surfaces of ZnO

Temperature-programmed desorption (TPD) was used to study the adsorption and reaction of CH3SH and (CH3)2S2 on the (0001) and (000) surfaces of ZnO. The interaction of these molecules with ZnO was found to be structure-sensitive. Both CH3SH and (CH3)2S2 adsorb dissociatively on ZnO(0001), forming adsorbed methylthiolate intermediates and only molecularly on ZnO(000). In the case of CH3SH, this result is consistent with that reported previously for the interaction of Br?nsted acids with ZnO and indicates that exposed cation-anion pairs are the active sites for dissociative adsorption. Only exposed Zn cations are required for the dissociative adsorption of (CH3)2S2. Methylthiolate species produced by dissociative adsorption of CH3SH and (CH3)2S2 on ZnO(0001) were found to undergo a variety of reaction pathways, including coupling to produce dimethyl sulfide and oxidation to formaldehyde, CO, and CO2. Pathways for the production of these various products are proposed.     

Combined perturbative-variational investigation of the vibrations of CHBr(3) and CDBr(3)

A full dimensional vibrational treatment of CHBr(3) and CDBr(3) using Van Vleck perturbation theory followed by a variational calculation is presented. The calculation of a force field, and its adjustment for better match with experiment, is discussed. The computed eigenstates and spectral features are compared to experiment. Changes in intensities of the nu(1) and 2nu(4) bands upon simple alterations of the dipole moment expansion are described.     

Calculated spectroscopic and electric properties of the alkali metal-ammonia complexes from Kn-NH3 to Frn-NH3 (n=0,+1)

The newly developed Stuttgart small-core scalar relativistic pseudopotentials for the alkali metals are used to study spectroscopic and electric properties of the heavier alkali metal-ammonia complexes from K(n)-NH(3) to Fr(n)-NH(3) (n=0,+1) at the second-order Moller-Plesset (MP2) and coupled cluster [CCSD(T)] levels of theory. Equilibrium geometries and dissociation energies computed at the MP2 level are in reasonable agreement with their CCSD(T) counterparts, whereas for the dipole polarizabilities MP2 is not performing well overestimating significantly electron correlation effects. The bond distances increase monotonically with increasing mass of the metal atom as relativistic effects are small in these systems. However, the dipole polarizabilities are more sensitive to such effects and we find a decrease in this property from Cs-NH(3) to Fr-NH(3). Combination of CCSD(T) harmonic frequencies and MP2 anharmonic corrections obtained from a perturbative vibrational treatment leads to fundamental frequencies in good agreement with experimental results obtained by Suzer and Andrews [J. Am. Chem. Soc. 109, 300 (1986)]. We also present the results of variational calculations with a three-dimensional vibrational Hamiltonian, making use of CCSD(T) potential energy and electric dipole moment surfaces. Complexation of NH(3) to the metal causes a strong infrared intensification of the symmetric NH(3) stretching mode in the neutral complexes, which is absent in the charged species.     

Luminescence and microstructures of Eu(3+)-doped Ca9LiGd(2/3)(PO4)7

A red-emitting phosphor, Eu(3+)-doped Ca(9)LiGd(2/3)(PO(4))(7), was synthesized by the conventional high-temperature solid-state reaction. X-ray powder diffraction (XRD) analyses confirmed the pure crystalline phase of Whitlockite-type structure. The excitation spectra of Eu(3+) doped Ca(9)LiGd(2/3)(PO(4))(7) were measured in the VUV and UV region indicating an efficient energy transfer process from the host and Gd(3+) to Eu(3+) ions. Upon excitation with VUV and UV radiation, the phosphor showed strong red emission around 611 nm corresponding to the forced electric dipole (5)D(0)→(7)F(2) transition of Eu(3+) ions. The VUV- and UV-excited luminescence spectra of Ca(9)LiGd(2/3)(PO(4))(7):Eu(3+) together with the dependence of the integrated emission intensities on the doping levels were investigated. The Eu(3+) ions were investigated by a tunable laser as an excitation source. The excitation spectra of (7)F(0)→(5)D(0) transitions suggest that there are two families of inequivalent sites for Eu(3+) in this host. The concentration quenching and crystallographic site-occupancy of Eu(3+) ions in Ca(9)LiGd(2/3)(PO(4))(7) host were discussed on the basis of the site selective excitation and emission spectra, the luminescence decay and its crystal structure.