Search results for "Bond cleavage"

Controlled rearrangement of lactam-tethered allenols with brominating reagents: a combined experimental and theoretical study on α- versus β-keto lac…

2011

N-Bromosuccinimide (NBS) smoothly promotes the ring expansion of lactam-tethered allenols to efficiently afford cyclic α- or β-ketoamides with good yields and high chemo-, regio-, and diastereoselectivity, through controlled C-C bond cleavage of the β- or γ-lactam nucleus. Interestingly, in contrast to the rearrangement reactions of 2-azetidinone-tethered allenols, which lead to the corresponding tetramic acid derivatives (β-keto lactam adducts) as the sole products, the reactions of 2-indolinone-tethered allenols under similar conditions give quinoline-2,3-diones (α-keto lactam adducts) as the exclusive or major products. To rationalize the experimental observations, theoretical studies ha…

Theoretical Elucidation of β-O-4 Bond Cleavage of Lignin Model Compound Promoted by Sulfonic Acid-Functionalized Ionic Liquid

2019

While the depolymerization of lignin to chemicals catalyzed by ionic liquids has attracted significant attention, the relevant molecular mechanism, especially the cleavage of specific bonds related to efficient depolymerization, still needs to be deeply understood for the complexity of this natural aromatic polymer. This work presents a detailed understanding of the cleavage of the most abundant β-O-4 bond in the model system, guaiacylglycerol β-guaiacyl ether, by a Brønsted acidic IL (1-methyl-3-(propyl-3-sulfonate) imidazolium bisulfate ([C3SO3Hmim][HSO4]) using density functional theory calculation and molecular dynamics simulation. It has been found that [C3SO3Hmim][HSO4] generates zwit…

Efficient DNA Cleavage Induced by Copper(II) Complexes of Hydrolysis Derivatives of 2,4,6‐Tri(2‐pyridyl)‐1,3,5‐triazine in the Presence of Reducing A…

2007

The reaction of 2,4,6-tri(pyridyl)-1,3,5-triazine (ptz) and copper(II) salts in dmf/water (1:1) results in the hydrolysis of ptz and formation of the anions bis(2-pyridylcarbonyl)amide (ptO2–) and bis(2-pyridylamine)amide (ptN2–), which are found in the complexes [Cu(ptN2)(OAc)]·3H2O (1), [Cu(ptO2)(OAc)(H2O)]·H2O (2), [Cu(ptN2)(for)]·3H2O (3) (for = formate), [Cu(ptO2)(for)(H2O)] (4), [Cu(ptO2)(benz)]·H2O (5) (benz = benzoate), and [Cu(ptO2)F(H2O)]2·3H2O (6). This report includes the chemical and spectroscopic characterization of all these complexes along with the crystal structures of 4–6. The coordination spheres of CuII in 4 and 5 are best described as distorted tetragonal square pyramid…

Simultaneous substitution of bridging acetate groups and reversible RhC bond cleavage in [Rh2(O2CCH3)3-{(C6H4)PPh2}(HO2CCH3)2] in the presence of CF…

1993

Abstract The reaction of the monometallated compound [Rh2(O2CCH3)3 {(C6H4)PPh2}(HO2CCH3)2] (1) with CF3CO2H at room temperature yields [Rh2(O2CCF3)3{(C6H4)PPh2}(HO2CCF3)2] (3) as the only isolable product. Compound 3 has been characterized by X-ray methods. 3 crystallizes in the space group P21 / n. It contains three trifluoroacetate groups bridging a Rh4+2 unit with a RhRh bond distance of 2.438(1) Ă; the fourth bridging ligand is a triphenylphosphine metallated at one of the ortho positions. Two molecules of trifluoroacetic acid occupy the axial coordination positions. In addition to the substitution of acetate groups, reversible electrophilic RhC bond activation is observed.

Stereoselective Synthesis of (+)-11βH,13-Dihydroestafiatin, (+)-11βH,13-Dihydroludartin, (−)-Compressanolide, and (−)-11βH,13-Dihydromicheliolide fro…

2002

Starting from 2 and 3, obtained from santonin (1), we have synthesized natural guaianolides 4-7. Chemoselective epoxidation of 2 gave (+)-11betaH,13-dihydroestafiatin (4), and epoxidation of 3 followed by regioselective elimination of the hydroxyl group afforded (+)-11betaH,13-dihydroludartin (5). Sharpless' mild regioselective ring-opening of 4 and 5 followed by hydrogenolysis yielded (-)-compressanolide (6) and (-)-11betaH,13-dihydromicheliolide (7), respectively.

A Density Functional Study of Open-Shell Cyclopentadienyl−Molybdenum(II) Complexes. A Comparison of Stabilizing Factors: Spin-Pairing, Mo−X π Bonding…

2000

International audience; The dissociation of PH3 from the 18-electron system CpMoX(PH3)3 to afford the corresponding 16-electron CpMoX(PH3)2 fragment has been investigated theoretically by density functional theory for X = H, CH3, F, Cl, Br, I, OH, and PH2. The product is found to prefer a triplet spin state for all X ligands except PH2, the singlet−triplet gap varying between 1.7 kcal/mol for OH to 8.7 kcal/mol for F. The Mo−PH3 bond dissociation energy to the 16-electron ground state varies dramatically across the series, from 4.5 kcal/mol for OH to 23.5 kcal/mol for H, and correlates with experimental observations on trisubstituted phosphine derivatives. Geometry-optimized spin doublet Cp…

Photo Induced Radical Reactions

2012

This article discusses a number of reactions of potential synthetic interest occurring through photochemically generated organic radicals. Emphasis is placed on the nature of the resulting photoproducts, whose formation is discussed on a mechanistic basis. If available, experimental evidence (obtained by laser flash photolysis or related time-resolved techniques) is provided. The material is organized according to the reaction types, for instance, homolytic cleavage, mesolytic cleavage, radical addition, and oxidative or reductive electron transfer. In addition to the classical carboncarbon or carbonhydrogen bond breaking processes, such as the Norrish type I reaction, the hydrogen abstract…

1967

Durch Viskositatsmessungen und spektroskopische Bestimmung des gebildeten Monomeren wird der saurekatalysierte Abbau von Poly-3,4-acrolein verfolgt. Er erfolgt fast ausschlieslich durch Kettenspaltung; eine Depolymerisation tritt nur in untergeordnetem Mase auf. Diese im Vergleich zu anderen polymeren Aldehyden unerwarteten Ergebnisse werden mit dem Auftreten eines durch Resonanz stabilisierten Kettenendes bei der Spaltung erklart. The acid-catalyzed degradation of poly-3,4-acrolein was investigated by viscosity and spectroscopic determination of the monomer formed. The degradation occurs predominantly by chain scission; depolymerization is of minor importance. The results are unexpected in…

Synthesis of various natural 8,12-elemanolides from artemisin

1989

Abstract This paper describes the chemical transformations of artemisin into various natural 8,12-elemanolides.

Collision-Induced Dissociation of Imidazolium-Based Zwitterionic Liquids

2009

Fragmentation pathways of some imidazolium based zwitterionic liquids—3-(3-alkyl-1-imidazolio)-propane sulfonates and 3-(2-methyl-3-alkyl-1-imidazolio)-propane sulfonates—have been studied by tandem electrospray mass spectrometry and collision-induced dissociation. The relative abundances of the lowest energy fragment ions depend on the length of the alkyl chain at the IIN of the imidazolium ring and the cone voltage. The first fragment ions originate from the scission of Cnon aromatic–N bond of compounds investigated, but with increasing collision energy, scission of C–C bonds occurs. Aggregates of the general formula [(M + H) x + (M) y]+ ( x;y = 1–2) formed. Methyl substituted zwitterion…