Search results for "nucleophile"
showing 10 items of 385 documents
On the reactivity of 3-bromo-2-nitrobenzo[ b ]thiophene with nucleophiles: elucidation of the base-catalysed mechanism with rearrangement
2001
Abstract The reactivity of 3-bromo-2-nitrobenzo[b]thiophene (1) with several (anionic and neutral) nucleophiles has been examined. Only with neutral, weak nucleophiles (as anilines) 1 gives, in the presence of non-nucleophilic bases (triethylamine or potassium carbonate), together with the ‘expected’ 3-amino-2-nitrobenzo[b]thiophenes (3) also the ‘unexpected’ 2-amino-3-nitrobenzo[b]thiophenes (4). The composition of the final isomeric mixture depends on the base added (nature and quantity) and on the solvent used. The results demonstrate the relevance of base-catalysis and support a reaction pathway involving the formation of an anionic intermediate (B) which undergoes addition of a second …
Organometallic nucleophiles.A mechanistic study of halide displacement at saturated carbon by 2- and 4-pyridyl complexes of palladium (II) and platin…
1996
Abstract The reactions of the 2- and 4-pyridyl complexes [MX(C 5 H 4 N C n )(dppe)] and trans -[MX(C 5 H 4 N C n )(PPh 3 ) 2 ] (M Pd, Pt; X Cl, Br; n = 2, 4)- involving halide displacement from the organic halides XCH 2 R (X Cl, Br; R CN, Ph, CH CH 2 ) by the pyridyl nitrogen have been studied kinetically by conductivity in acetone or acetonitrile at 25°C. The kinetic data fit the second-order rate law rate k 2 [XCH 2 R][complex], in agreement with an S N 2 process at saturated carbon. The higher rates are displayed by the 2-pyridylplatinum derivatives with X Br in both the metal complex and the organic halide. The higher nucleophilic power of the 2-pyridyl complexes compare…
A DFT study of the ionic [2+2] cycloaddition reactions of keteniminium cations with terminal acetylenes
2015
Abstract The molecular mechanism of the ionic [2+2] cycloaddition (I-22CA) reactions of a keteniminium cation (KC) with acetylene and propyne has been investigated using DFT methods at the MPWB1K/6-311G(d,p) level. These I-22CA reactions take place via a two-step mechanism. The first step is the nucleophilic attack of these alkynes on the central carbon of KC, yielding cyclopropene intermediates, while the second step corresponds to the conversion of these intermediates into more stable cyclobuteniminium cations (CCs). The first step is the rate-determining step, while the second step is responsible for the formation of the two regioisomeric CCs experimentally observed in the reaction with …
Modular Phosphole-Methano-Bridged-Phosphine(Borane) Ligands. Application to Rhodium-Catalyzed Reactions
2012
The synthesis of the phospholyl(phosphinoborane)methane air- and moisture-stable hybrid ligands 4a–f, starting from 1-phenylphospholes 1a–d, was performed via P–C bond coupling on the methano bridge. Two strategies were investigated, according to the phospholyl moiety used as a nucleophilic or an electrophilic reagent. In the first pathway, the phospholyl anions react with the easily available (chloromethyl)diphenylphosphine–borane 3 to afford ligands 4a–d in 29–67% isolated yields. In the second pathway, the phospholyl(dicyclohexylphosphinoborane)methane ligands 4e,f were synthesized in 18–23% yields, through a nucleophilic substitution on the cyanophosphole. Removal of the BH3 moiety on 4…
No carrier-added nucleophilic aromatic radiofluorination using solid phase supported arenediazonium sulfonates and 1-(aryldiazenyl)piperazines
2012
Abstract This Letter concerns the investigation of a solid phase based method for no carrier-added nucleophilic [ 18 F]fluorination of aromatic compounds via de-diazofluorination. Initial screening of reaction conditions was conducted using soluble analogues, that is, substituted benzenediazonium tosylates and 1-(phenyldiazenyl)piperazines in solution. This was followed by translation of the principle conditions to solid phase bound analogues. A variety of substituted aryldiazonium cations were immobilised using a sulfonate functionalised ion exchange resin and labelled with [ 18 F]fluoride ion by Balz–Schiemann like thermal decomposition in the presence of no carrier-added [ 18 F]fluoride …
PREPARATION AND REACTIONS OF 2-PYRIDYLPLATINUM(II) COMPLEXES [PTCL(C5H4N-C2)(TERTIARY PHOSPHINE)2] - COMPOUNDS WITH A MARKEDLY NUCLEOPHILIC PYRIDINE …
1989
Abstract The 2-pyridyl complex trans -[PtCl(C 5 H 4 N- C 2 )(PPh 3 ) 2 ] (I) can be prepared in high yield by oxidative addition of 2-chloropyridine to [Pt(PPh 3 ) 4 ]. The reaction of I with 1,2-bis(diphenylphosphino)ethane yields the cis derivative [PtCl(C 4 5 H 4 N- C 2 )(dppe)] (II). In polar solvents, the latter rearranges to the binuclear cationic complex [Pt(μ-C 5 H 4 N- C 2 , N )(dppe)] 2 Cl 2 . The reaction of I with [PdCl(η 3 -2-MeC 3 H 4 )] 2 (1/0.5 molar ratio) gives the products [PtCl(μ-C 5 H 4 N- C 2 , N )(PPh 3 )] 2 (IV) and [PdCl(η 3 -2-MeC 3 H 4 )(PPh 3 )]. 31 P NMR monitoring of the reaction suggests that PPh 3 transfer occurs in a binuclear platinum/palladium intermediate…
Photoinduced molecular rearrangements. The photochemistry of 1,2,4-oxadiazoles in the presence of sulphur nucleophiles. Synthesis of 1,2,4-thiadiazol…
1997
Abstract The photochemistry of some 1,2,4-oxadiazoles in the presence of sulphur nucleophiles has been investigated. Irradiation of the 5-amino-3-phenyl- and 3,5-diphenyl-1,2,4-oxadiazole at γ = 254 nm in methanol in the presence of sodium hydrogen sulphide or thiols gave a photo-induced redox reaction at the ring ON bond, leading to the corresponding N -substituted benzamidines. By contrast, irradiation of the 5-amino-3-phenyl-1,2,4-oxadiazole in the presence of thioureas or thiocarbamates, essentially gave 3-phenyl-5-substituted 1,2,4-thiadiazoles, which presume an NS bond formation between the ring-photolytic species and the sulphur nucleophile. In turn, irradiation of the same 5-amino…
Organocatalytic enantioselective synthesis of 2,5,5-trisubstituted piperidines bearing a quaternary stereocenter. Vinyl sulfonamide as a new amine pr…
2020
An organocatalytic desymmetrizing intramolecular aza-Michael reaction with vinyl sulfonamides as nucleophilic nitrogen source has been devised for the synthesis of a new family of 2,5,5-trisubstituted piperidines bearing a quaternary sterocenter. The process takes place with excellent levels of enantioselectivity and moderate to good diastereoselectivity. The vinyl sulfonamide moiety can be removed by means of an ozonolysis reaction.
Phosphororganische Verbindungen, 85. Kinetische Untersuchungen der Umsetzung organischer Phosphorverbindungen mit Nucleophilen und Supernucleophilen
1977
Bei der alkalischen Spaltung von quartaren Phosphoniumsalzen und tertiaren Phosphinoxiden zeigt HOO⊖ keinen α-Effekt. Die Spaltung der P–C-Bindung wird auch nicht durch Gruppen erleichtert, welche uber die Ausbildung von H-Brucken den Angriff von HOO⊖ am Phosphoniumzentrum fordern. — In Ubereinstimmung mit den Ergebnissen anderer Autoren wird bei der Hydrolyse der Phosphin-, Phosphon- und Phosphorsaureester 1, 2 und 3 in Gegenwart von H2O2 ein α-Effekt beobachtet, der sich in einer Hydrolysebeschleunigung um einen Faktor von ca. 100 ausdruckt. Die Hydrolysegeschwindigkeit nimmt sowohl mit HO⊖ als auch mit HOO⊖ entsprechend folgender Reihenfolge ab: Diphenylphosphinsaure-(p-nitrophenyl)ester…
Carboranyl Substituted Siloxanes and Octasilsesquioxanes: Synthesis, Characterization, and Reactivity
2008
Carboranyl-containing disiloxane, cyclic-siloxane and cage-like silsesquioxane have been prepared in high yields. Two routes are compared for their preparation, a classical hydrolytic process based on hydrolysis and condensation of the freshly prepared carboranylalkylchlorosilane and ethoxysilane precursors and a nonhydrolytic route based on the specific reactivity of chorosilane toward DMSO. Based on the typical reactivity of the carboranyl group toward nucleophiles, dianionic disiloxanes and octaanionic silsesquioxanes were obtained without modification of the siloxane bond. Products are fully characterized by FTIR, NMR and MALDI-TOF methods.