Search results for "reactions"
showing 10 items of 631 documents
Stopped-Flow and DFT Studies of Proton Transfer and Isomerization of 5-Amino-3-imino-1,2,6,7-tetracyano-3H-pyrrolizine and Its Related Base 2-(5-Amin…
2001
International audience; A complete kinetic study of pH-dependent isomerization of 5-amino-3-imino-1,2,6,7-tetracyano-3H-pyrrolizine (HL) and 2-(5-amino-3,4-dicyano-2H-pyrrol-2-ylidene)-1,1,2-tricyanoethanide (L‘-) in the pH range from −0.5 to +13 in aqueous solution, which spans over 7 orders of magnitude for the pseudo-first-order rates (log k from −4.8 to +2.5), has revealed for the first time the existence of the corresponding conjugate species L- and HL‘. The study has allowed the determination of the acid dissociation constants of HL (pKa) and HL‘ (pKa‘), as well as all of the individual forward and reverse isomerization rates of the acidic (HL/HL‘) and basic (L-/L‘-) forms. Although L…
Synthesis of brominated tetrathiafulvalenes via phosphite-mediated cross-coupling
2010
The synthesis of polybrominated tetrathiafulvalenes (TTF-Brn, 2-4) containing 2-4 bromine atoms via phosphite-mediated cross-coupling of bromo-substituted 1,3-dithiole-2-thiones and 1,3-dithiole-2-ones is reported. © 2010 Elsevier B.V.
Carbon nitride as photocatalyst in organic selective transformations
2020
Abstract Graphitic carbon nitride (g-C3N4) is a metal-free conjugated polymer which has become a new research hotspot in photocatalysis. It can be used for solar energy exploitation like in solar energy organic synthesis, one of the most new and appealing green applications of heterogeneous photocatalysis. This chapter resumes the state-of-the-art and progresses in the application of heterogeneous visible light photocatalysis in organic selective transformations by using C3N4 as photocatalyst.
A new strategy for the synthesis of fluorinated 3,4-dihydropyrimidinones
2009
A new family of 3,4-dihydropyrimidinones (DHPMs) bearing fluorinated substituents at C6 have been prepared from gem-difluorinated nitriles, alkyl 3-butenoates and iso(thio)cyanates. This novel Biginelli-type process relies on the gamma-addition of the ester-derived enolate to fluorinated nitriles. A tandem nucleophilic addition aza-Michael reaction sequence completes the synthetic process. (C) 2009 Elsevier B.V. All rights reserved.
Overview on oxidation mechanisms of organic compounds by TiO2 in heterogeneous photocatalysis
2012
This review provides the reader with a general overview on heterogeneous photocatalytic oxidation mechanisms in the presence of TiO2, with a special address to conversion of aliphatic and aromatic organic species. The aim was to clarify the steps of the photo-oxidation of the various classes of compounds and to relate them with the properties of the catalysts and the experimental conditions used. Reactions carried out to perform complete degradation and photocatalytic partial oxidations have been deeply discussed. Recent isotopic studies highlighted new reaction pathways concerning partial oxidation of alcohols to aldehyde and oxidation of benzene while EPR investigations confirmed that not…
A Headful of T4 Coliphage DNA Packaged to Fasces-Like Globules in Fractal Models
1998
We present a new model for T4 DNA packaging based on fractal considerations. The proposed model is based on electron microscopic observations of spread and packaged DNA. The model takes into account enzymatically and unidirectionally driven packaging, and quick release of the DNA during infection. We also consider the different biochemical reactions of the packaging process.
1,2,4-Oxadiazole rearrangements involving an NNC side-chain sequence.
2009
The thermal rearrangement of N-1,2,4-oxadiazol-3-yl-hydrazones into 1,2,4-triazole derivatives is reported. This represents the first example of a three-atom side-chain rearrangement involving an NNC sequence linked at the C(3) of the oxadiazole. The reactions carried out under solvent-free conditions produced good to high yields of the final products.
Palladium-based catalytic systems for the synthesis of conjugated enynes by Sonogashira reactions and related alkynylations
2007
Conjugated alkynes are recurring building blocks in natural products, a wide range of industrial intermediates, pharmaceuticals and agrochemicals, and molecular materials for optics and electronics. The palladium-catalyzed cross-coupling between sp(2)-hybridized carbon atoms of aryl, heteroaryl, and vinyl halides with sp-hybridized carbon atoms of terminal acetylenes is one of the most important developments in the field of alkyne chemistry over the past 50 years. The seminal work of the 1970s has initiated an intense search for more general and reliable reaction conditions. The interest in the catalytic activation of demanding substrates, the need to minimize the consumption of depletive r…
Organocatalytic Domino Oxa-Michael/1,6-Addition Reactions: Asymmetric Synthesis of Chromans Bearing Oxindole Scaffolds.
2016
An asymmetric organocatalytic domino oxa-Michael/1,6-addition reaction of ortho-hydroxyphenyl-substituted para-quinone methides and isatin-derived enoates has been developed. In the presence of 5 mol % of a bifunctional thiourea organocatalyst, this scalable domino reaction affords 4-phenyl-substituted chromans bearing spiro-connected oxindole scaffolds and three adjacent stereogenic centers in good to excellent yields (up to 98 %) and with very high stereoselectivities (up to >20:1 d.r., >99 % ee).
Neutron halos in the excited states of 12B
2018
The differential cross sections of the 11B(d,p) 12B reaction leading to formation of the 1+ ground state and the 0.95-MeV 2+, 1.67-MeV 2−, 2.62-MeV 1−, 2.72-MeV 0+, and 3.39-MeV 3− excited states of 12B are measured at Ed = 21.5 MeV. The analysis of the data is carried out within the coupled-reaction-channels method for the direct neutron transfer and the Hauser-Feshbach formalism of the statistical compound-nucleus model. The spectroscopic factors, asymptotic normalization coefficients, and rms radii of the last neutron in all states studied are deduced. The existence of the neutron halos in the 1.67-MeV 2− and 2.62-MeV 1− states is found, consistent with the earlier published data. New in…