Kinetics of Electron-Transfer Oxidation of Alkyl Radicals by Copper(II) Complexes

Abstract

That the decrease in R, on monosubstitution in the 3position, is not reflected in a change of may be attributed to the only other variable in eq. 5, i.e., DE. The term DE is a dielectric constant in name only, being a function of the shape of the molecule (for a spherical model the square of the ratio of the distance of the protons from the center of the sphere and the radius of the sphere), the dielectric constant of the molecule, and the dielectric constant of the solvent.The lack of sensitivity of ^ to changes in R on monosubstitution may be ascribed to an opposite and almost equal change in DE. In unsubstituted glutaric acid the electrostatic influence of carboxyl groups occur primarily through the low dielectric of the molecular backbone since, due to solvation of the polar carboxyl groups, the molecule exists in an extended conformation. Monosubstitution in the 3-position brings about a decrease in R accompanied by a greater fraction of the electrostatic effect occurring through the high dielectric of the solvent, and the decrease in R is matched by an increase in DE so that the product of DeR in eq. 5 is not significantly altered. The conformational changes brought about by 3-gem substitution are greater than those brought about by the monosubstituents examined, and most of the electrostatic interaction occurs through the solvent so that DE is essentially constant and the product of RDE becomes smaller with increasing steric requirements of the gem substituents.By the reasoning presented above the similar influence of 3-gem substitution on log Ki/Ko and log kT[k0 and the grossly greater sensitivity of log kT/k0 to 3-monosubstitution is explained.

Copper-Catalyzed Oxidative Dehydrogenative Carboxylation of Unactivated Alkanes to Allylic Esters via Alkenes

“… 31 Consistent with this observation, Kochi reported that nitrogen-ligated Cu(II) complexes oxidize alkyl radicals to alkenes more slowly than do simple Cu(II) salts. 32 , 33 Although these reactions with ligated copper occurred in lower yield than those with simple copper halides, they did give substantial amounts of product and were valuable for studying the mechanism of this reaction ( vide infra ).…”

“…The mechanism for the initial conversion of cyclohexane to cyclohexene likely proceeds by abstraction of a hydrogen atom from cyclohexane by a tert -butoxy radical to generate a cyclohexyl radical, which undergoes oxidation to the alkene. The oxidation of alkyl radicals to olefins by copper–peroxide systems has been studied by Kochi 32 , 39 and Walling. 40 Their studies imply that oxidation of the cyclohexyl radical formed in the current system likely generates cyclohexyl cation, which undergoes deprotonation to form the alkene.…”

Free-Radical Rearrangements

“…Although there is little quantitative information regarding the rates of 1,4-aryl migrations, these reactions would appear to be reasonably fast when they are strongly exothermic as, for example, in the conversion of a primary alkyl radical to a tertiary (87) (compare the 1,2-aryl shifts). By utilizing data concerning the cyclization (both Ar r 5 and Ar 2 -6) of 4-phenylbutyl and its oxidation by cupric ion (93) and accepting a value of ~10 8 M" 1 sec -1 as the rate constant for the oxidation (94), the rate constant for the cyclization can be calculated to be ca. 1-5 x 10 4 sec" 1 at 150°C.…”

“…93 94 7-Octenyl radicals undergo slow but regiospecific 1,7 ring closure [k lt7 « 7 x 10 2 sec -1 at 65°C (755)]. 93 94 7-Octenyl radicals undergo slow but regiospecific 1,7 ring closure [k lt7 « 7 x 10 2 sec -1 at 65°C (755)].…”

New chiral bidentate ligands containing thiazolyl and pyridyl donors for copper-catalyzed asymmetric allylic oxidation of cyclohexene

“…The copper-catalyzed allylic oxidation (KharashSosnovsky reaction) of olefins with peresters has been the subject of numerous synthetic and mechanistic investigations [1][2][3][4][5][6][7][8][9][10]. The allylic ester product of the reaction can easily be converted into allylic alcohol by saponification or reduction method.…”