Electrochemical Nonacidic N‐Nitrosation/N‐Nitration of Secondary Amines through a Biradical Coupling Reaction

Abstract

An acid-free N-nitrosation/nitration of the NÀ H bonds in secondary amines with Fe(NO 3) 3 • 9H 2 O as the nitroso/nitro source through an electrocatalyzed radical coupling reaction was developed. Cyclic aliphatic amines and N-heteroaromatic compounds were N-nitrosated and N-nitrated, respectively, under mild conditions. Control and competition experiments, as well as kinetic studies, demonstrate that N-nitrosation and N-nitration involve two different radical reaction pathways involving N + and N * radicals. Moreover, the electrocatalysis method enables the preferential activation of the NÀ H bond over the electrode and thus provides high selectivity for specific N atoms. Finally, this strategy exhibits a broad scope and provides a green and straightforward approach to generate useful N-nitroso/nitro compounds in good yields.

The Use of Potassium/Sodium Nitrite as a Nitrosating Agent in the Electrooxidative N‐Nitrosation of Secondary Amines

“…Electrosynthesis could be used to achieve electron transfer between the electrodes and substrates or catalysts, thus avoiding the use of excess exogenous oxidants and would eliminate the generation of waste products. Very recently, Lu reported on an electrochemical N ‐nitrosation/ N ‐nitration of secondary amines through a biradical coupling strategy [16] . The method employed a nitroso radical as the nitrosating agent which was generated in situ from the well‐known thermal decomposition of iron(III) nitrate nonahydrate, Fe(NO 3 ) 3 ⋅ 9H 2 O.…”

“…Very recently, Lu reported on an electrochemical N-nitrosation/Nnitration of secondary amines through a biradical coupling strategy. [16] The method employed a nitroso radical as the nitrosating agent which was generated in situ from the wellknown thermal decomposition of iron(III) nitrate nonahydrate, Fe(NO 3 ) 3 • 9H 2 O. In the light of our continuous interest in organic electrosynthesis and NÀ H functionalization, we envisioned that N-nitrosation might be generally achieved by the direct activation of sodium/potassium nitrite through electrochemical strategies.…”

Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis

“…Lu and co–workers recently reported electrochemical methods for the N -nitration of azole heterocycles and the N -nitrosation of secondary alkylamines through intermolecular N–N bond formation ( Scheme 95 ). 303 Cross-selectivity for N–N bond formation has generally been difficult to achieve, making this method noteworthy. Substrate electrolysis was performed in an undivided cell under constant current conditions, in the presence of Fe(NO 3 ) 3 nonahydrate as the nitration/nitrosation reagent and n -Bu 4 N + BF 4 – as supporting electrolyte in MeCN at 70 °C.…”

Electrochemical Functionalization of Imidazopyridine and Indazole: An Overview

“…However, no direct reported methodology for electrochemical nitration of indazole is reported so far in the literature. In 2020, Lu et al [47] . first introduced an example of acid‐free electrochemical N ‐1 nitration of 1 H ‐indazole 36 a using Fe(NO 3 ) 3 ⋅ 9H 2 O 51 as nitrating agent and n Bu 4 NBF 4 as electrolyte.…”