TEMPO–Me: An Electrochemically Activated Methylating Agent

Abstract

Bench-and air-stable 1-methoxy-2,2,6,6-tetramethylpiperidine (TEMPO-Me) is relatively unreactive at ambient temperature in the absence of an electrochemical stimulus. In this report, we demonstrate that the one-electron electrochemical oxidation of TEMPO-Me produces a powerful electrophilic methylating agent in situ. Our computational and experimental studies are consistent with methylation proceeding via a SN2 mechanism, with a strength comparable to the trimethyloxonium cation. A protocol is developed for the electrochemical methylation of aromatic acids using TEMPO-Me.

Mesolytic Versus Homolytic Cleavage in Photochemical Nitroxide-Mediated Polymerization

“…This is consistent with experimental observations for the oxidative cleavage of the corresponding TEMPO-based analogues. [12][13][14][15] If the results above were to apply also to corresponding the excited state mesolytic cleavage, it would suggest styrene actually undergoes photoinitiated cationic polymerization with this PNMP agent (which would still be consistent with the observed control), and the acrylates in particular struggle to undergo cleavage at all, which could help to explain the failed experiments with this monomer. While most of the trends in the calculations of Figure 3 would be mirrored in the excited state mesolysis energies, there are two important differences: (1) the excited states are higher in energy and this additional energy can help to overcome the otherwise unfavorable Gibbs free energies requirements;…”

“…The mesolytic pathway may lend itself to other synthetically useful photoreactions, outside that of NMP applications, analogous to our recent use of formally oxidized alkoxyamines as in situ methylation agents. 14 ASSOCIATED CONTENT…”

“…Experiments have shown that the exact specific cleavage behavior depends on the leaving group and the presence or absence of nucleophiles including coordinating solvents such as acetonitrile (see Scheme 3). [12][13][14][15] As seen in Scheme 3, in the oxidized species at least, cleavage to a carbon-centered radical is expected for acrylate and methacrylate polymerizations, but not for styrene which will produce carbocations. 12 Summing up, while it has been assumed until now that PNMP proceeds via energy transfer and standard homolytic cleavage, the possibility of mesolytic cleavage and its implications has not been explored.…”

Functionalized Silicon Electrodes Toward Electrostatic Catalysis

“…By changing the anodization time applied upon alkoxyamine monolayers, one is able to control the density of active carbocations and hence the coverage of a formed redox probe tagged monolayer. This proof-of-concept experiment expands the electrostatic effect to the regulation of organic electrosynthesis ( Norcott et al, 2019 ).…”

Enhanced Photocatalytic Properties of PET Filaments Coated with Ag-N Co-Doped TiO2 Nanoparticles Sensitized with Disperse Blue Dyes

“…However, an opposite rule is observed in the ESR spectra of h + radicals (Figure 7g). A weaken signal of h + radicals (equal to strong eradicals) is detected in dark owing to the electrophilicity of TEMPO [78]. As the irradiation time is prolonged, the peak intensity of eradicals is drastically reduced, suggesting that a large number of h + radicals are generated in the P-2 filaments under visible light irradiation.…”