19693-75-5Relevant articles and documents
Iridium-catalysed allylic substitution: Stereochemical aspects and isolation of IrIII complexes related to the catalytic cycle
Bartels, Bjoern,Garcia-Yebra, Cristina,Rominger, Frank,Helmchen, Guenter
, p. 2569 - 2586 (2007/10/03)
Ir-catalysed allylic alkylations of enantiomerically enriched monosubstituted allylic acetates proceed with up to 87% retention of configuration using P(OPh)3 as ligand. High retention enantioselectivity of up to 86% ee in asymmetric allylic alkylations of achiral or racemic substrates is achieved with monodentate phosphorus amidites as ligands. Lithium N-tosylbenzylamide was identified as a suitable nucleophile for allylic aminations. Of particular importance is the use of lithium chloride as an additive, generally leading to increased enantioselectivities. Two (π-allyl)IrIII complexes were characterised by X-ray crystal structure analysis and spectroscopic data.
Photosensitized (electron transfer) carbon-carbon bond cleavage of radical cations: the 2-phenylethyl ether and acetal systems
Arnold, Donald R.,Lamont, Laurie J.
, p. 2119 - 2127 (2007/10/02)
The scope of the photosensitized (electron transfer) carbon-carbon bond cleavage involving radical cations has been defined for 2-phenylethyl ethers and acetals.The thresholds for reactivity of the monophenylethyl and gem-diphenylethyl derivatives are compared.While the radical cation of methyl 2,2-diphenylethyl ether (7) cleaves to give ultimately diphenylmethane (2) and dimethoxymethane (8), the radical cation of methyl 2-phenylethyl ether (9) was stable under these conditions.In contrast to the lack of reactivity of the radical cation of 9, the radical cations of methyl 2-phenyl-2-propyl ether (11), methyl 2-phenylcyclopentyl ether (13), and 2-phenylmethyl-1,3-dioxolane (16) cleave.Cleavage in the monophenylethyl series is limited to formation of a carbocation at least as stable as the secondary α-oxyalkyl or di-α-oxyalkyl.The basis for predicting this type of reactivity of radical cations is defined.The rate of carbon-carbon bond cleavage is increased the oxidation potential of the molecule, by decreasing the carbon-carbon bond strength, and (or) by decreasing the oxidation potential of that fragment that will become the carbocation.The results obtained from the reactions of 2-diphenylmethyl-1,3-dioxolane (14) and 2-phenylmethyl-1,3-dioxolane (16) cast doubt on the published oxidation potential for the 1,3-dioxolan-2-yl radical.Key words: photochemistry, radical cation, electron transfer, bond cleavage, radical.
INDIRECT ELECTROCHEMICAL α-METHOXYLATION OF ALIPHATIC ETHERS AND ACETALS - REACTIVITY AND REGIOSELECTIVITY OF THE ANODIC OXIDATION USING TRIS(2,4-DIBROMOPHENYL)AMINE AS REDOX CATALYST
Ginzel, Klaus-Dieter,Steckhan, Eberhard,Degner, Dieter
, p. 5797 - 5806 (2007/10/02)
The technically important α-methoxylation of aliphatic ethers and acetals to form mixed acetals respectively aldehydes or ortho-esters can be performed electrochemically at low potentials in methanol solution using an undivided cell and tris(2,4-dibromophenyl)amine as redox catalyst.The regioselectivity is usually considerably higher as compared with direct electrolysis in the abscence of a catalyst.Especially valuable is the method for the regioselective methoxylation of secondary carbon atoms in presence of primary or tertiary ones and of the acetal carbon in 1,3-dioxolanes.The redox catalyst is stable under the reaction conditions so that more than thousand turnovers could be obtained.
The Reactions of Electron-Rich Heterocycles with Derivatives of Orthocarboxylic Acids; VIII. Proton Acid-Catalyzed Acylation of Indoles by 2-Alkoxy-1,3-dioxolanes
Akguen, Eyuep,Tunali, Mustafa,Pindur, Ulf
, p. 397 - 401 (2007/10/02)
In acid-catalyzed reactions with 3-unsubstituted indoles 1, 2-alkoxy-1,3-dioxolanes 2a-c behave as acyl equivalents.Depending on the substitution patterns of the reaction partners, the 1,3-dioxolanium ions 3a-c, generated in situ from the cyclic ortho esters by the action of sulfosalicylic acid, react to form tris-(3-indolyl)alkanes 6 and 9, bis-(3-indolyl)ethenes 7, or 3-benzoylindoles 8.Analogous reactivity was observed with related acyclic ortho esters.
Radiation Chemical Production and Lifetimes of Trialkoxymethyl Carbocations in Aqueous Solution
Steenken, S.,Buschek, J.,McClelland, R. A.
, p. 2808 - 2813 (2007/10/02)
Trialkoxymethyl radicals were produced in aqueous solution by H abstraction from trialkoxymethanes by OH and H.The radicals were then oxidized by one-electron transfer to give trialkoxymethyl carbocations.The reactions of the cations with water and with OH- were studied by using time-resolved conductance techniques. (CH3O)3C+ hydrolyzes with a rate constant of (1.4 +/- 0.2)E3 s1- and it reacts with OH- with k = (7 +/- 1)E7 M1-s1-.The activation parameters for the reaction with water are EA = 7.6 kcal/mol and ΔS(excit.) = -20.2 eu.Replacement of methoxy in the cation by ethoxy and isopropoxy leads to a pronounced decrease in the rate constants for these processes: the Taft ρ* values for the reaction of (RO)3C+ with H2O and OH- are 5.7 and 3.7, respectively.With cyclic trialkoxymethyl cations that from the six-membered 1,3-dioxane system is more stable than that from 1,3-dioxolane, the five-atom counterpart.Trialkoxymethyl cations are also produced by a β-fragmentation reaction from α-(β-trialkoxy)methoxyalkyl cations.
