Search results for "Reactivity"

Structure and photoreactivity of stable zwitterionic group 6 metal allenyls

2013

The synthesis and mechanistic study of the unprecedented reactivity of a series of zwitterionic η(1)-metal allenyls are reported.

A DFT study of the asymmetric (S)-5-(pyrrolidin-2-yl)-1H-tetrazole catalyzed Michael addition of carbonyl compounds to nitroalkenes

2007

Abstract The role of the ( S )-5-(pyrrolidin-2-yl)-1 H -tetrazole in the asymmetric organocatalyzed Michael addition of carbonyl compounds to nitroalkenes has been studied using DFT methods at the B3LYP/6-31G ∗∗ computational level. For the C–C bond-formation step, several reactive channels have been analyzed. The B3LYP/6-31G ∗∗ results, which are in reasonable agreement with the experiments, allow us to explain the stereoselectivity and the increase of the reactivity achieved by an intramolecular HB between the acid hydrogen of the tetrazole moiety and one oxygen atom of the nitroalkene.

Aminobis(phenolate)s of imidomolybdenum(VI) and -tungsten(VI)

2009

Abstract The reactions of trans-[MoO(ONOMe)Cl2] 1 (ONOMe = methylamino-N,N-bis(2-methylene-4,6-dimethylphenolate) dianion) and trans-[MoO(ONOtBu)Cl2] 2 (ONOtBu = methylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenolate) dianion) with PhNCO afforded new imido molybdenum complexes trans-[Mo(NPh)(ONOMe)Cl2] 3 and trans-[Mo(NPh)(ONOtBu)Cl2] 4, respectively. As analogous oxotungsten starting materials did not show similar reactivity, corresponding imido tungsten complexes were prepared by the reaction between [W(NPh)Cl4] with aminobis(phenol)s. These reactions yielded cis- and trans-isomers of dichloro complexes [W(NPh)(ONOMe)Cl2] 5 and [W(NPh)(ONOtBu)Cl2] 6, respectively. The molecular st…

Reactivity and Structural Defects in Glaserite-Type Iron-Vanadates

2018

Optical, Electrochemical, and Catalytic Properties of the Unsaturated Host Pd3(dppm)3(CO)2+and Pd4(dppm)4(H)2+2Clusters: An Overview

2004

This paper presents an overview of the optical, photophysical, and photochemical properties including UV-visible and luminescence spectra in solution at 298 and 77 K, along with electrochemical, and catalytic behavior under reduction conditions (for both thermally and electrochemically assisted systems) of the tri- and tetranuclear Pd3(dppm)3(CO)2+ and Pd4(dppm)4(H)2+ 2 clusters (dppm=bis(diphenylphosphino)methane). This review is also complemented with relevant information about their syntheses, molecular and electronic structures supported from computer modeling, EHMO and DFT calculations, and their host-guest behavior with anions and neutral molecules, in relation with their observed rea…

Influenza A virus infection inhibits the efficient recruitment of Th2 cells into the airways and the development of airway eosinophilia.

2003

Abstract Most infections with respiratory viruses induce Th1 responses characterized by the generation of Th1 and CD8+ T cells secreting IFN-γ, which in turn have been shown to inhibit the development of Th2 cells. Therefore, it could be expected that respiratory viral infections mediate protection against asthma. However, the opposite seems to be true, because viral infections are often associated with the exacerbation of asthma. For this reason, we investigated what effect an influenza A (flu) virus infection has on the development of asthma. We found that flu infection 1, 3, 6, or 9 wk before allergen airway challenge resulted in a strong suppression of allergen-induced airway eosinophil…

Cross-Metathesis Reactions as an Efficient Tool in the Synthesis of Fluorinated Cyclic β-Amino Acids

2009

The synthesis of enantiomerically pure, cyclic, gamma,gamma-difluorinated beta-amino acids with various ring sizes has been carried out with a cross-metathesis (CM) reaction being one of the key steps, followed by a Dieckmann-type condensation to bring about the cyclization. Subsequent catalytic hydrogenation under microwave irradiation with (-)-8-phenylmenthol as a chiral auxiliary led to the successful chemo- and diastereoselective chemical reduction of the resulting cyclic beta-enamino esters. The efficiency and scope of the CM reaction with different types of fluorinated imidoyl chlorides and unsaturated esters has also been studied in order to determine the optimal reaction conditions …

Synthesis of a New Fluorinated Oxazolidinone and Its Reactivity as a Chiral Auxiliary in Aldol Reactions.

2007

A new enantiomerically pure fluorinated oxazolidinone has been prepared from a fluorinated imidoyl chloride and an optically pure sulfoxide. The diastereoselective reduction of the β-iminosulfoxide thus formed followed by elimination of the sulfoxide and cyclization of the created aminoalcohol furnishes the desired product. The fluorinated oxazolidinone was subsequently used as a chiral auxiliary in Aldol reactions. We also found that the selective formation of the syn-Evans and syn-non-Evans diastereoisomer can be controlled by adjusting the Lewis acid/base ratio.

Regio- and stereoselective synthesis of the enantiomers of monoterpene-based β-amino acid derivatives

2007

Abstract The regio- and stereospecific addition of chlorosulfonyl isocyanate to cis-δ-pinene enantiomers has furnished monoterpene-fused β-lactams. The observed regioselectivity can be explained by ab initio DFT modeling of transition state structures. In contrast with the less reactive α-pinane-fused β-lactam 4, the resulting β-lactams 5 and 13 containing an amino group connected to a secondary carbon possess similar reactivity to the cycloalkane-fused analogues and can be easily converted to the β-amino acid and its protected derivatives. The base-catalyzed isomerization of the cis-amino ester afforded the corresponding trans-amino ester in moderate yield.

Visible-light driven oxidation of gaseous aliphatic alcohols to the corresponding carbonyls via TiO2 sensitized by a perylene derivative

2013

Sensitized P25 TiO2 was prepared by wet impregnation with a home-prepared perylene dye, i.e., N,N?-bis(2-(1- piperazino)ethyl)-3,4,9,10-perylene-tetracarboxylic acid diimide dichloride (PZPER). Energy levels of PZPER were found to be compatible with those of TiO2 allowing fast electron transfer. The obtained catalyst has been characterized and used in the gas-phase partial oxidation of aliphatic primary and secondary alcohols, i.e., methanol, ethanol, and 2- propanol. The reaction was carried out under cut-off (?> 400 nm) simulated solar radiation in O2 atmosphere. The perylene derivative allowed a good absorbance of visible radiation thanks to its low optical energy gap (2.6 eV) which was …