A novel domino (4+2)/(4+2)/(3+2) cycloaddition reaction leading to highly functionalized polycyclic nitroso acetals

2-Methoxybuta-1,3-diene reacts under high pressure conditions in a one-pot domino (4+2)/(4+2)/(3+2) cycloaddition reaction with a dienophile, β-nitrostyrene and a dipolarophile to give tri, tetra and pentacyclic nitroso acetals. In this novel domino reaction up to six bonds and up to eight stereogenic centers are created in one step in good yield and good stereoselectivity.     

An unexpected bispericyclic transition structure leading to 4+2 and 2+4 cycloadducts in the endo dimerization of cyclopentadiene

The stereospecific endo dimerization of cyclopentadiene takes place through an asynchronous and symmetrical bispericyclic transition structure, which shows a merging of the 4+2 and 2+4 cycloaddition paths. The shape of the transition structure testifies to the presence of attractive Salem/Houk secondary orbital interactions assisting the endo approach.     

Ru(II)-catalyzed [2 + 2 + 2] cycloaddition of 1,2-bis(propiolyl)benzenes with monoalkynes leading to substituted anthraquinones

[2 + 2 + 2] cycloadditions of 1,2-bis(propiolyl)benzenes with monoalkynes were effectively catalysed by Cp*RuCl(cod) under mild conditions to give substituted anthraquinones in moderate to high yields.     

Behavior of Co4+ ion in K2NiF4-type (Ca1+xSm1−x)CoO4

Orthorhombic K₂NiF₄-type (Ca_1+xSm_1−x)CoO₄ (0.00 ≤ x ≤0.15) with space group Bmab has been synthesized by the polymerized complex route. The cell parameters (a and b) decrease, while the cell parameter (c) increases with increasing Co⁴⁺ ion content. The global instability index (GII) indicates that the crystal stability of (Ca_1+xSm_1−x)CoO₄ is not influenced by the Co⁴⁺ ion content. (Ca_1+xSm_1−x)CoO₄ is a p-type semiconductor and exhibits hopping conductivity in the small-polaron model at low temperatures. The magnetic measurement indicates that (Ca_1+xSm_1−x)CoO₄ shows paramagnetic behavior above 5 K, and that the spin state of both the Co³⁺ and Co⁴⁺ ions is low. The Co⁴⁺ ion acts as an acceptor, and the electron transfer becomes active through the Co³⁺–O–Co⁴⁺ path as the Co⁴⁺ ions increase.     

15NH4+ ion movement inside d(G4T4G4)2 G-quadruplex is accelerated in the presence of smaller Na+ ions

2D NMR studies demonstrate that the residence lifetime of 15NH4+ ions within the bimolecular G-quadruplex adopted by d(G4T4G4) is reduced from 270 ms in the presence of ammonium ions alone to 36 ms in the presence of Na+ ions.     

Anionic polymerization of 4-methyl-2-oxetanone (β-butyrolactone)

Polymerization of 4-methyl-2-oxetanone ( 1 ) initiated with potassium acetate-dibenzo-18-crown-6 complex ( 2 ) in THF as solvent, was studied. Transfer reactions, leading to both crotonate anions and carboxylic acid formation, have been observed. Two kinetic effects of these reactions, hampering the living polymerization, have been established. The first results from reinitiation with the crotonate anions and thereby lowers the polymer molecular weight. The second is the decrease in the overall polymerization rate due to complexation of the growing carboxylate anions with carboxylic acid moieties. Kinetic scheme of polymerization involves propagation accompanied by transfer followed by slow reinitiation. This scheme, including complexation of the active species has been solved numerically. The apparent rate and equilibrium constants (k_p, k_tr, k_ri, and K_ass and respectively) have been determined. Although these kinetic parameters depend strongly on the polymerization conditions, but the ratio of the rate constants k_p : k_t : k_ri is fairly constant and equal to 10⁻⁴ : 10⁻⁶ : 10⁻⁶, respectively (at 20°C). Conditions of the controlled anionic synthesis of the amorphous poly(4-methyl-2-oxetanone) with $\bar M_n$ as high as 1.7 × 10⁴ and ${{ \le \bar M_n } \mathord{\left/ {\vphantom {{ \le \bar M_n } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }} \le 1.20$ have also been elaborated.     

Palladium-catalyzed alkoxycarbonylation of (Z)-2-en-4-yn carbonates leading to 2,3,5-trienoates

Pd(0)-catalyzed carbonylation of (Z)-2-en-4-yn carbonates in the presence of a balloon pressure of CO in an alcohol donates vinylallenyl esters with an exclusively E-configuration and in high yields. The fact that no such reactivity could be observed with E-configured enyne carbonates may indicate that the reaction is promoted via the cooperative coordination of palladium with both alkynyl and carbonate moieties.     

High-pressure (2+2)cycloaddition of toluene-4-sulphonyl isocyanate to glycals

High-pressure (2+2)cycloaddition of toluene-4-sulphonyl isocyanate to glycals is examined. Reactions proceed regiospecifically to afford single products in case of all 3-substituted glycals. Upon heating or even after standing at room temperature adducts undergo retro-addition to give starting glycals. Various aspects of the cycloaddition are discussed, especially ret-ro-reaction and rearrangement of β-lactams to α,β-unsaturated amides.     

An equilibrium analysis of the aqueous H+-MoO4(2-)-(HP)O(3)2- and H+-MoO4(2-)-(HP)O(3)2--HPO4(2-) systems

The speciation in the phosphitomolybdate system, H+-MoO4(2-)-(HP)O(3)2-, has been determined from combined potentiometric and 31P NMR measurements in 0.600 M Na(Cl) medium at 298(1) K. Potentiometric titration data were collected in the ranges 2.5<-log[H+]<6.2, 40.0相似文献   

Photophysics of Anionic Bis(4H-imidazolato)CuI Complexes

In this paper, the photophysical behavior of four panchromatically absorbing, homoleptic bis(4H-imidazolato)Cu^I complexes, with a systematic variation in the electron-withdrawing properties of the imidazolate ligand, were studied by wavelength-dependent time-resolved femtosecond transient absorption spectroscopy. Excitation at 400, 480, and 630 nm populates metal-to-ligand charge transfer, intraligand charge transfer, and mixed-character singlet states. The pump wavelength-dependent transient absorption data were analyzed by a recently established 2D correlation approach. Data analysis revealed that all excitation conditions yield similar excited-state dynamics. Key to the excited-state relaxation is fast, sub-picosecond pseudo-Jahn-Teller distortion, which is accompanied by the relocalization of electron density onto a single ligand from the initially delocalized state at Franck-Condon geometry. Subsequent intersystem crossing to the triplet manifold is followed by a sub-100 ps decay to the ground state. The fast, nonradiative decay is rationalized by the low triplet-state energy as found by DFT calculations, which suggest perspective treatment at the strong coupling limit of the energy gap law.     

Mechanisms of water oxidation catalyzed by the cis,cis-[(bpy)2Ru(OH2)]2O4+ ion

The cis,cis-[(bpy)(2)Ru(III)(OH(2))](2)O(4+) micro-oxo dimeric coordination complex is an efficient catalyst for water oxidation by strong oxidants that proceeds via intermediary formation of cis,cis-[(bpy)(2)Ru(V)(O)](2)O(4+) (hereafter, [5,5]). Repetitive mass spectrometric measurement of the isotopic distribution of O(2) formed in reactions catalyzed by (18)O-labeled catalyst established the existence of two reaction pathways characterized by products containing either one atom each from a ruthenyl O and solvent H(2)O or both O atoms from solvent molecules. The apparent activation parameters for micro-oxo ion-catalyzed water oxidation by Ce(4+) and for [5,5] decay were nearly identical, with DeltaH(++) = 7.6 (+/-1.2) kcal/mol, DeltaS() = -43 (+/-4) cal/deg mol (23 degrees C) and DeltaH(++) = 7.9 (+/-1.1) kcal/mol, DeltaS(++) = -44 (+/-4) cal/deg mol, respectively, in 0.5 M CF(3)SO(3)H. An apparent solvent deuterium kinetic isotope effect (KIE) of 1.7 was measured for O(2) evolution at 23 degrees C; the corresponding KIE for [5,5] decay was 1.6. The (32)O(2)/(34)O(2) isotope distribution was also insensitive to solvent deuteration. On the basis of these results and previously established chemical properties of this class of compounds, mechanisms are proposed that feature as critical reaction steps H(2)O addition to the complex to form covalent hydrates. For the first pathway, the elements of H(2)O are added as OH and H to the adjacent terminal ruthenyl O atoms, and for the second pathway, OH is added to a bipyridine ring and H is added to one of the ruthenyl O atoms.     

A phosphine-catalyzed [3+2] cycloaddition strategy leading to the first total synthesis of (-)-hinesol

In one step, the skeleton of cis-spirovetivanes was constructed with high stereoselectivity by the phosphine-catalyzed [3+2] cycloaddition reaction of tert-butyl 2,3-butadienoate or 2-butynoate with 3-methyl-2-methylenecyclohexanone (5). This method was exemplified by the first highly efficient total synthesis of natural product (-)-hinesol, which is an active ingredient of cerebral circulation and metabolism improvers.     

Nd3+ and Am3+ ion interactions with sulfate ion and their influence on NdPO4(c) solubility

The effects of Nd(III)/Am(III) complexation with sulfate were studied by 1) re-examining existing data for the Am–SO₄ system using more, advanced aqueous electrolyte models valid to high concentration to obtain reliable thermodynamic data for SO ₄ ^2– complexes or ion interactions with Nd³⁺ and Am³⁺ and 2) conducting experimental solubility studies of NdPO₄(c), an analog phase of AmPO ₄ (c), a possibly important phase in high level nuclear wastes, in the presence of SO ₄ ^2– to test the newly developed thermodynamic model and show the possible influence of sulfate in a repository environment. The data showed that the increase in the solubility of NdPO ₄ (c) resulted primarily from the increase in ionic strength. Slightly higher observed Nd concentrations in the presence of sulfate, as compared with concentrations predicted at the experimental ionic strengths, resulted from the weak complexes or ion interactions involving Nd ³⁺ –SO ₄ ^2– . The Pitzer ion interaction parameters, applicable to 0.5m sulfate, were obtained for Am ³⁺ –SO ₄ ^2– from a reinterpretation of known solvent extraction data. These parameters are also consistent with literature data for Am ³⁺ /Na⁺ exchange and solvent extraction in the presence of sulfate. When used for the analogous Nd ³⁺ –SO ₄ ^2– system to predict NdPO ₄ (c) solubility in the presence of sulfate, they provided excellent agreement between the predicted and the observed solubilities, indicating that they can be reliably used to determine Nd ³⁺ or Am ³⁺ ion interactions with SO ₄ ^2– in all ground waters where SO ₄ ^2– is less than 0.5m     

Novel intramolecular (4 + 1) and (4 + 2) annulations of halopolyenes by cascade radical reaction

Free radical reaction of vinyl iodides having dinenoate function in the presence of tributyltin hydride or tris(trimethylsilyl)silane caused a sequential cyclization reaction to produce (4 + 1) and (4 + 2) annulated compounds by means of a cascade radical reaction. Stereogenic centers of the cascade reaction were highly controlled. On the contrary, the cathodic electrolysis of the vinyl iodides afforded monocyclic compounds.     

Vibrational study of (NH4)2HPO4 and (ND4)2DPO4 single crystals. The PO4 ion vibration couplings

The PO₄ internal vibrations have been studied by measuring the polarized infrared (IR) spectra at room temperature (RT) and at low temperature (LT=20K) as well as the polarized Raman (R) spectra. The i.r. dichroism in the (010) plane is investigated in a great range of angles α (0°<α<135°) of the electric vector E with respect to the crystallographic axic c. Some intra ion couplings are inferred. No factor group splitting is observed in the RT IR spectra. However, simultaneously regarding the LT IR spectra and the R spectra promotes an interchain coupling inside the primitive cell. Strong resonance coupling effects are found for the PO₄ stretching modes with the in-plane mode δOH(δOD).     

Structure of the UO2 2+-SO 4 2- ion pair in aqueous solution

The structure of the ion pairs formed in aqueous uranyl sulfate solutions has been investigated with high-energy X-ray scattering. Sulfate binds to the uranyl as a monodentate ligand in equimolar solutions. The geometry of the ion pair is very similar to configurations found in crystalline structures; in particular, the U-O-S angle is bent in solution as well as in the solid state. It can therefore be concluded that an U-O-S angle of 143 degrees is an intrinsic property of the uranyl sulfate bond and not due to packing effects or interaction with the water in the primary solvation shell.