Search results for "double bond"
showing 10 items of 184 documents
Naphthothiete und ihre Anwendung in der Heterocyclen-Synthese
1995
Naphtothietes and Their Application to the Synthesis of Heterocycles The three isomeric naphthothietes 5, 11, and 16 were prepared according to the reaction sequences shown in Schemes 1–3. The final step was in each case a flash vacuum pyrolysis (FVP) of the corresponding mercaptonaphthalenemethanol 4, 9, and 15, respectively. The thiete rings in 5 and 11 can be opened by gentle heating; the ring opening of the isomer 16 possesses a much higher activation barrier. A MNDO calculation of the ΔHf values of 5, 11, and 16 and the open isomers 5′, 11′, and 16′ provides an explanation for the different behavior. Photochemical ring opening represents a useful alternative. The reaction Schemes 4, 6,…
The transformation of aromatic molecules into the subspace of their double bonds
1975
A model of new submolecules is presented. As an application some absorptions of aromatic radicals are interpreted in UV and visible spectra. Extension of the model to biological systems is prejudged.
ChemInform Abstract: Cycloaddition Reactions of Benzothiete and Hetero Dienophiles for the Synthesis of Heterocyclic Systems.
1987
Abstract Benzothiete ( 1 ) undergoes cycloaddition reactions with hetero dienophiles with NN-, NO- or CO- double bonds, leading to six-membered heterocyclic ring systems of 2H-3,4-dihydro-1,2,3-benzothiadiazine ( 3 ), 4H-3,1,2-benzoxathiazine ( 4 ) and 4H-3,1-benzoxathiin.
ChemInform Abstract: Synthetic Approaches to Antiinflammatory Macrolactones of the Oxacyclododecindione Type.
2015
A variety of attempts to synthesize oxacyclododecindione macrolactones through carbonylative ring-closure, intramolecular alkyne hydroacyalation, and Ru-catalyzed double bond isomerization fails.
Cycloaddition Reactions of 2H-Benzo[b]thiete and Thiocarbonyl Compounds
1997
2H-Benzo[b]thiete (1) reacts in the o-quinoid form 1′ with the cyclic trithiocarbonates 4 and 6a, b and with the thioketones 8, 10 and 12 in [8π + 2π] cycloaddition reactions to the spiro compounds 5, 7a, b, 9, 11a, b. Irrespective of the presence of CC double bonds, chemoselective and regioselective addition processes at the CS double bonds take place that lead to 4H-1,3-benzodithianes.
A new C–C bond formation model based on the quantum chemical topology of electron density
2014
ELF topological analyses of bonding changes in non-polar, polar and ionic organic reactions involving the participation of CC(X) double bonds make it possible to establish a unified model for C–C bond formation. This model is characterised by a C-to-C coupling of two pseudoradical centers generated at the most significant atoms of the reacting molecules. The global electron density transfer process that takes place along polar and ionic reactions favours the creation of these pseudoradical centers at the most nucleophilic/electrophilic centers of the reacting molecules, decreasing activation energies. The proposed reactivity model based on the topological analysis of the changes in electron…
ChemInform Abstract: A New C-C Bond Formation Model Based on the Quantum Chemical Topology of Electron Density
2014
ELF topological analyses of bonding changes in non-polar, polar and ionic organic reactions involving the participation of CC(X) double bonds make it possible to establish a unified model for C–C bond formation. This model is characterised by a C-to-C coupling of two pseudoradical centers generated at the most significant atoms of the reacting molecules. The global electron density transfer process that takes place along polar and ionic reactions favours the creation of these pseudoradical centers at the most nucleophilic/electrophilic centers of the reacting molecules, decreasing activation energies. The proposed reactivity model based on the topological analysis of the changes in electron…
ChemInform Abstract: Lithium Enediolates and Dienediolates of Carboxylic Acids in Synthesis: Alkylation with Secondary Halides.
2010
Abstract High yields in the alkylation of dianions of α,β-unsaturated carboxylic acids with secondary halides can be obtained despite elimination reactions occurring. α-Regioselectivity for the alkylation of but-2-enoic acids ( 1–4 ) is seldom obtained. Although double bond stereoselectivity is higher than 99% for γ-alkylated products, stereoselectivity is rather poor for most of the α-alkylated products.
A molecular electron density theory study of the participation of tetrazines in aza-Diels–Alder reactions
2020
The reactions of eight tetrazines of increased electrophilic character with nucleophilic tetramethyl ethylene (TME) and with electrophilic tetracyanoethylene (TCE) have been studied using Molecular Electron Density Theory. These reactions are domino processes comprising an aza-Diels–Alder (ADA) reaction followed by an extrusion of molecular nitrogen, yielding a dihydropyridazine. Analysis of the conceptual DFT (CDFT) indices showed an increase of the electrophilicity and a decrease of the nucleophilicity of tetrazines with an increase of the electron-withdrawing character of the substituent. A very good correlation between the global electron density transfer at the transition structu…
Part II. Chiral dirhodium (II) catalysts with ortho-metalated arylphosphane ligands in the enantioselective intramolecular cyclopropanation of a race…
2006
Abstract In this report, chiral dirhodium (II) with ortho -metalated phosphane ligands, namely ( M )-Rh 2 (O 2 CR) 2 (PC) 2 [PC = ortho -metalated aryl phosphane, O 2 CR = carboxylate bridging ligands) ( 1a–g ), have been used for the intramolecular cyclopropanation of racemic1-diazo-6-methyl-3-(2-propenyl)-5-hepten-2-one ( 2 ), containing both a tri- and monosubstituted carbon–carbon double bond, in pentane. The highest level of regiocontrol has been obtained with chiral catalyst Rh 2 (O 2 CCH 3 ) 2 [( p -MeC 6 H 3 )P( p -MeC 6 H 4 ) 2 ] 2 ( M )- 1c , affording favorably trisubstituted cyclopropane 3 versus monosubstituted cyclopropane 4 in 74:26 ratio. An exceptional diastereoselectivity…