Electron‐Driven Nitration of Unsaturated Hydrocarbons

Abstract

Herein, we introduce an electrochemically assisted generation of nitryl radicals from ferric nitrate under mild reaction conditions using a simple setup with inexpensive graphite and stainless-steel electrodes. The mechanism of the reaction is supported by detailed spectroscopic and experimental studies. Powered by electricity and driven by electrons, the synthetic diversity of this reaction has been demonstrated through the development of highly efficient nitration protocols of various unsaturated hydrocarbons. In addition to a broad application area, these protocols are easy to scale for decagram quantities, and exhibit exceptional substrate generality and functional-group compatibility.

Nitration of Derivatives of Imidazo[1,5‐a]pyridine via C−H Functionalization with Fe(NO3)3 ⋅ 9H2O as a Promoter and a Nitro Source

“…The thermal decomposition of Fe(NO 3 ) 3 • 9H 2 O could generate a • NO 2 radical, which further attacks an arene substrate to afford a nitroarene. [64][65][66] The utilization of Fe-(NO 3 ) 3 • 9H 2 O as a nitro source has been explored by groups of Sun, [51] Punniyamurthy, [52] Zhang and Fan, [67] Huo, [68] Malik and Sharada [69] (Scheme 1). In their reactions, they either used CuCl 2 • 2H 2 O as a catalyst or 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) or 2-hydroxyisoindoline-1,3-dione (NHPI) as additives with the help of directing groups to obtain nitrated aniline derivatives and nitro-bearing heterocycles.…”

“…Fe(NO 3 ) 3 ⋅ 9H 2 O is a mild, nontoxic, inexpensive, easy‐to‐handle reagent. The thermal decomposition of Fe(NO 3 ) 3 ⋅ 9H 2 O could generate a ⋅ NO 2 radical, which further attacks an arene substrate to afford a nitroarene [64–66] . The utilization of Fe(NO 3 ) 3 ⋅ 9H 2 O as a nitro source has been explored by groups of Sun, [51] Punniyamurthy, [52] Zhang and Fan, [67] Huo, [68] Malik and Sharada [69] (Scheme 1).…”

Nitrative Difunctionalization of Alkenes via Cobalt-Mediated Radical Ligand Transfer and Radical-Polar Crossover Photoredox Catalysis

“…Focusing on these challenges, herein, we report an efficient dual cobalt-photoredox-induced nitrative difunctionalization system of alkenes for the preparation of 1,2-halonitro derivatives involving a unique cobalt-catalyzed RLT step and utilizing N -nitrosuccinimide as the organic nitrating reagent and ammonium salts as cost-effective halogen sources. In contrast to previous reports on bioinspired manganese- and iron-mediated RLT concepts, the radical rebound step with earth-abundant cobalt metal does not rely on the use of complex polydentate N -based ligands, making this process readily available. Mild and redox-neutral conditions allowed this method to have a broad scope with excellent regioselectivity for a variety of olefins.…”

Late-Stage C–H Nitration of Unactivated Arenes by Fe(NO3)3·9H2O in Hexafluoroisopropanol

“…However, as a result of its harsh reaction conditions, this methodology suffers from several serious drawbacks, such as poor selectivity, limited functional group tolerance, and potential environmental hazards. To address these shortcomings, many alternative protocols for the preparation of nitroarenes have been devised, including transition-metal-catalyzed cross coupling and C­(sp 2 )–H nitration, ipso -nitration reaction aromatic boronic acids and carboxylic acids, ipso -oxidation of aromatic azides and anilines, and nitrations using recently burgeoning techniques, such as flow chemistry, electrochemistry, photochemistry, and biocatalysis . Furthermore, to complement the mineral nitro sources generally utilized in these methodologies, various organic O -nitro- and N -nitro-type compounds (Figure b) have also been developed as novel nitro sources to provide more reliable nitration protocols under milder reaction conditions, , despite the fact that these new nitro sources have higher costs and a lower atom economy.…”