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.
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.
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.