2,2,6,6-tetramethylpiperidinooxy (TEMPO) is a versatile chemical reagent that can be used in a variety of chemical reaction systems.

Electrochemical triamination of alkynes

The use of 2,2,6,6-tetramethylpiperidinooxy (TEMPO) as a redox catalyst can be used for the electrocatalytic trifunctionalisation of alkynes to give controlled access to a variety of 2,3-diaminoindoles and 2,3-diaminoindoles. Mechanistic studies suggest that this triamino reaction may proceed via 5-endo-dig cyclisation of an N-centred radical and coupling with two consecutive radicals of a nitrile intermediate. In addition, this triamino reaction strategy allows for the simultaneous assembly of the indole scaffold and two additional amino substituents from an off-the-shelf aniline, which rapidly increases the complexity of the molecule and enables further synthetic transformations of the 2,3-diaminoindole core.

TEMPO-Mediated Dehydrogenative Hydroxyfluoroalkylation of Arylamines with Polyfluorinated Alcohols

In path a, a single-electron transfer from 1o to TEMPO generates the N-centered radical cationic species I, which is isomerized to the C-centered radical II. Meanwhile, α-hydrogen atom abstraction of 2a could deliver the key α-OH-trifluoroalkyl C-centered radical IV in the presence of TEMPO. Then, the cationic intermediate V is obtained via a radical/radical cross-coupling between intermediate II and intermediate IV. Eventually, deprotonation and rearomatization of intermediate V could give the target compound 3o. In path b, the direct addition of intermediate IV to arylamine 1o furnishes the radical intermediate VI, which could undergo a single-electron oxidation process followed by deprotonation to give the desired product 3o.

Electrochemical oxidation cross-coupling

A novel electrochemical method for the direct oxidative C-N coupling of tetrahydroquinolines and azoles leading to the synthesis of dihydroquinoline derivatives under mild reaction conditions. In this method, 2,2,6,6-tetramethylpiperidinooxy (TEMPO) can be used as a redox mediator and NaI can be used not only as an electrolyte but also as an iodine mediator. The reaction is characterised by good functional group tolerance and high atom economy to obtain the desired dihydroquinoline derivatives in moderate to excellent yields. In addition, the corresponding quinoline derivatives can be selectively obtained by adjusting the reaction conditions.

References:

[1] XIANGTAI MENG . Electrochemical triamination of alkynes: controllable synthesis of functionalized indolines and indoles?[J]. Green Chemistry, 2022. DOI:10.1039/d2gc01129h.

[2] XIAOYANG GAO, XUN CHEN*; TEMPO-Mediated Dehydrogenative Hydroxyfluoroalkylation of Arylamines with Polyfluorinated Alcohols[J]. The Journal of Organic Chemistry, 2024. DOI:10.1021/acs.joc.4c00185.

[3] DAN YANG . Electrochemical oxidative cross-coupling of tetrahydroquinolines and azoles?[J]. Green Chemistry, 2024. DOI:10.1039/d3gc04453j.