0000000000359028
AUTHOR
Jorge Royo
On the Reactivity of C(sp3)–H σ-Bonds: Oxygenation with Methyl(trifluoromethyl)dioxirane
The reactivity of C–H σ-bonds of a series of 2-substituted adamantanes 2 towards methyl(trifluoromethyl)dioxirane (1) shows a consistent dependence on the electron-withdrawing ability, either inductive or by resonance, of the substituent. The results are interpreted in terms of the ability of the substrate molecule to delocalize the electronic perturbation of the reacting center at the beginning of the reaction path. The model shows that the electronic demand from the reacting C–H σ-bond is transmitted along the substrate through a chain of hyperconjugative interactions, the relative intensities of which depend on the σ-bonds involved. The substrate molecule simultaneously provides positive…
Hyperconjugative Control by Remote Substituents of Diastereoselectivity in the Oxygenation of Hydrocarbons.
The oxidation of 2-substituted adamantanes (2) with TFDO (1) is reported. The data show a stereodifferentiation of the chemical environments induced by remote electron-withdrawing substituents which produces remarkable Z/E diastereoselectivity in the oxidation of the tertiary C(5)-H and C(7)-H bonds. The results show a bell-shaped correlation between the Z/E stereoselectivity and the substituent constant sigma(I), which is interpreted in terms of hyperconjugative stabilization of the diastereomeric transition states.
Mechanism of the Oxidation of Sulfides by Dioxiranes. 1. Intermediacy of a 10-S-4 Hypervalent Sulfur Adduct
Earlier studies established that dimethyldioxirane (1a) reacts with sulfides 2 in two consecutive concerted electrophilic oxygen-transfer steps to give first sulfoxides 3 and then sulfones 4. The same sequential electrophilic oxidation model was assumed for the reaction of sulfides 2 with the strongly electrophilic methyl(trifluoromethyl)dioxirane (1b). In this paper we report on a systematic and general study on the mechanism of the reaction of simple sulfides 2 with DMDO (1a) and TFDO (1b) which provides clear evidence for the involvement of hypervalent sulfur species in the oxidation process. In the oxidation of sulfides 2a-c, diphenyl sulfide (2d), para-substituted aryl methyl sulfides …
The oxidation of alkanes with dimethyldioxirane; a new mechanistic insight
Abstract Primary kinetic isotope effects were measured for the oxidation of cyclohexane and methylcyclohexane with DMDO in solution and in the gas phase. These experiments suggest an electrophilic oxygen insertion mechanism for the oxidation of alkanes by DMDO.
Oxygenation of Alkane C−H Bonds with Methyl(trifluoromethyl)dioxirane: Effect of the Substituents and the Solvent on the Reaction Rate
[Chemical reaction: See text] The mechanism of the oxygenation of alkane C-H bonds with methyl(trifluoromethyl)dioxirane (1a) is studied through the effect of the substituent and solvent on the rate of oxygenation of 2-substituted adamantanes (2). The results suggest a remarkable electron deficiency at the reacting carbon atom in the transition state leading to the regular oxygenation products. The linearity of the Hammett plot reveals that the reaction mechanism does not change within a range of 0.15-0.67 units of sigma(I). A change in the solvent does not affect the distribution of the products, indicating a through-bond transmission of the substituent effect as the origin of the deactiva…
Conformational mobility of thianthrene-5-oxide.
[reaction: see text] Data on the apparent dipole moment of thianthrene-5-oxide (1) and (1)H NMR spectra in different solvents support the conformational mobility of 1, which flaps between two limit boat conformations with the sulfinyl group in pseudoequatorial and pseudoaxial positions, respectively. The conformational equilibrium of 1 occurs too fast for the (1)H NMR (500 MHz) time-scale even at -130 degrees C, and the equilibrium constant has not been determined. The apparent dipole moments of 1 in n-hexane and 1,4-dioxane and the (1)H NMR spectra of 1 and the model compounds cis- and trans-thianthrene-5,10-dioxides (2) and thianthrene (5) in different solvents and at various temperatures…
Influence of Remote Substituents on the Equatorial/Axial Selectivity in the Monooxygenation of Methylene C−H Bonds of Substituted Cyclohexanes
The reactivity of individual C--H bonds in the methyl(trifluoromethyl)dioxirane TFDO oxygenation of stereogenic methylene groups in conformationally homogeneous monosubstituted cyclohexanes (2) has been determined. The unexpectedly high occurrence of O-atom insertion into C--H(ax) bonds suggests an in plane trajectory attack in the oxygenation while the diastereoselectivity of the reaction is qualitatively interpreted on the basis of the distinct hyperconjugative stabilization by the substituent of diastereomeric transition states due to long-range through bond interactions.
Mechanism of the oxidation of sulfides by dioxiranes: conformational mobility and transannular interaction in the oxidation of thianthrene 5-oxide.
The detailed study of the oxidation of thianthrene 5-oxide (1) with methyl(trifluoromethyl)dioxirane (5b) in different solvents and in the presence of (18)O isotopic tracers is reported. Thianthrene 5-oxide (1) is a flexible molecule in solution, and this property allows for transannular interaction of the sulfoxide group with the expected zwitterionic 7 and hypervalent 10-S-4 sulfurane 9 intermediates formed in the oxidation and biases the course of the reaction toward the monooxygenation pathway.