Substitution, oxidation induced

A study195 based on the NMR lanthanide-induced shifts (LIS) for a series of cis- and trans-3-substituted, and 3,3-disubstituted thietane oxides concluded that all cis-substituted oxides (5c R = CH3, t-Bu and aryl) exist exclusively in the diequatorial conformation. The trans-3-substituted isomers (185) prefer the equatorial oxygen conformation (R = CH3,86% t-Bu, 65-75% aryl, 75%), which means an axial preference for the substituents (e.g. 185d), at least when they are bound to a shift reagent (equation 75). 

Complexes 15 and 16 were also shown to undergo oxidatively induced substitution of MeCN for CO. In this case, however, doubly substituted derivatives were obtained via the singly substituted species, which could not be isolated, but was detected by CV [40]. 

Another example of a coupling reaction initiated by reaction of the radical anion with an electrophile is the reductive coupling of substituted 4/f-pyran-4-thiones (34) in the presence of alkyl halides (Scheme 8) [110,111]. The neutral radical formed by alkylation at sulfur is apparently not reduced at the potential of the electrolysis but undergoes dimerization. If the substrate is methylated prior to reduction, the sulfonium cation is reduced more easily than the neutral substrate to give the same dimeric product. The initially formed dimer (35) eliminates disulfide in an oxidatively induced process during the electrolysis, yielding the final bipyranilidene (36) [110]. 

On the basis of the analysis of the stereochemical outcome of oxidatively induced palladium-catalyzed C(sp )-0 forming reactions leading to substituted tetrahydrofurans, it was suggested that high valent alkyl palladium intermediates can react via a concerted three-center reductive elimination mechanism to form C (sp )-O bonds [31]. No characterization of these presumed high valent species or mechanistic studies of their reactions have been carried out. 

Redox reactions can be catalyzed by reducible cations substituted into the framework of zeolitic systems as well as polymorphic AIPO4 systems or by cations not located in the framework but in the micropores. In Chapter 8 we will discuss more extensively catalysis by Tia,Si(i 2,)02 systems using peroxides. Here we will initiate the discussion on redox catalysis with Coa Al(i 2.)P04 oxidation catalysts where reducible ions such as Co + substitute for AP+. Catalytic oxidation carried out with oxygen provides an opportunity to discuss radical-type chemistry. A second system that we will discuss is photochemical oxidation induced by the strong electrostatic field of ion-exchanged cations. We will subsequently discuss catalysis by Fe " " and Fe " " ion exchanged zeolites with comparisons to Zn + systems and the important role of the corresponding oxycation. 

Oxidatively-Induced and Electron-Transfer Catalysed Substitution of Isocyanide or Cyanide ligands for CO. 

OXIDATIVELY INDUCED, ELECTROCATALYTIC LIGAND SUBSTITUTION IN 17-ELECTRON MANGANESE COMPLEXES AN INVESTIGATION OF THE KINETICS BY DERIVATIVE CYCLIC VOLTAMMETRY... 

Oxidatively Induced, Electrocatalytic Ligand Substitution in 17-Electron Manganese Complexes an Investigation of the Kinetics by Derivative Cyclic Voltammetry M. TVset, V. Skagestad and V.D. Parker... 

Photolysis Chemical decomposition by the action of radiant energy Photooxidation Oxidation induced by radiant energy Refracture Index Measure of the biodegradability of a compound Sorption Reversible binding of a pollutant to a solid matrix Substituted Compound Replacement of one or more hydrogen atoms with other atoms or groups... 

T -dienyliron cations (Scheme 4-97) (c/ Section 2.5.2.b). Oxidatively induced reductive elimination of (pentenediyl)iron complexes gives vinylcyclopropanesJ 2-226] Depending on the substitution pattern and the conditions applied in some cases the reaction proceeds with retention of the configuration, whereas sometimes inversion of the configuration at the vinylcyclopropyl carbon is observed in combination with an inversion of the configuration at the double bond. The latter has been proven by monodeuteration of the terminal vinylic carbon atom. ... 

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