A Common, Facile and Eco‐Friendly Method for the Reduction of Nitroarenes, Selective Reduction of Poly‐Nitroarenes and Deoxygenation of N‐Oxide Containing Heteroarenes Using Elemental Sulfur

Abstract

A transition metal‐free, environment‐friendly and practical protocol was developed either for the reduction of nitroarenes or for the deoxygenation of N‐oxide containing heteroarenes. The reaction proceeded with the use of a non‐toxic and cheap feedstock as elemental sulfur in aqueous methanol under relatively mild conditions. Green chemistry credentials were widely favorable compared to traditional and industrial protocols with good E‐factors and a low production of waste. The strategy allowed the efficient reduction of a large variety of substituted‐nitroarenes including various o‐nitroanilines as well as selective reduction of various poly‐nitroarenes in excellent yields with a broad substrate scope. The protocol was successfully extended to the deoxygenation of some N‐oxide containing heteroarenes, like benzofuroxans, phenazine N,N'‐dioxides, pyridine N‐oxides, 2H‐indazole N1‐oxides, quinoxaline N1,N4‐dioxides and benzo[d]imidazole N1,N3‐dioxides. A gram‐scale example for the synthesis of luminol, in green conditions, was reported. A solid mechanism of reaction was proposed from experimental evidences.

Microwave‐assisted reduction of aromatic nitro compounds with novel oxo‐rhenium complexes

“…[11] That is one of the reasons why methods that avoid the use of metals are necessary. Procedures are reported in the literature that include the use of just organic reducing agents, such as sodium dithionite (Na 2 S 2 O 4 ) in presence of an electron-transfer catalyst, [12] elemental sulphur in presence of NaOH, [13] phenyl(2-quinolyl)methanol (PQM) as organocatalyst in presence of stoichiometric amounts of NaBH 4 or NaCNBH 3, [14] 9,10-dihydroanthracene (DHA),…”

“…[ 11 ] That is one of the reasons why methods that avoid the use of metals are necessary. Procedures are reported in the literature that include the use of just organic reducing agents, such as sodium dithionite (Na 2 S 2 O 4 ) in presence of an electron‐transfer catalyst, [ 12 ] elemental sulphur in presence of NaOH, [ 13 ] phenyl(2‐quinolyl)methanol (PQM) as organocatalyst in presence of stoichiometric amounts of NaBH 4 or NaCNBH 3, [ 14 ] 9,10‐dihydroanthracene (DHA), xanthene or tetralin at 230–300°C, [ 15 ] charcoal in subcritical water [ 16 ] and graphene‐oxide with hydrazine hydrate as the hydrogenation agent. [ 17 ] Functionalized amines can be accessed not only through the reduction of nitro groups but also by means of metal‐catalysed CN coupling.…”

Reduction of Nitroarenes via Catalytic Transfer Hydrogenation Using Formic Acid as Hydrogen Source: A Comprehensive Review

“…The first is catalyzed by specific transition metals such as iron, nickel, palladium or platinum in presence of molecular hydrogen under special pressure conditions, [8b,10-16] whereas the second strategy employs hydrogen sources for the transfer hydrogenation process such as hydrides (e. g. NaBH 4 or hydrosilanes, [17][18][19][20][21][22][23][24][25] hydrazine hydrate, [17,[26][27][28][29][30] organic reagents (e. g. alcohol, glycerol or formic acid) [17,[31][32][33] and more recently, boron reagents. [34][35] Other methods based on reduced sulfur reagents like elemental sulfur, [36][37] dithionite [38] or sulfides [39] are useful for the reduction of nitro group, being particularly convenient for the selective reduction of polynitroarenes. From Green Chemistry point of view, the catalytic hydrogenation have received enormous attention by their improvements compared to Bechmap's reduction; [17] however, this type of strategies presents some drawbacks such as the use of specialized equipment and safety issues related to H 2 storage, the manipulation of flammable hydrogen gas and the use of hazardous reagents and sophisticated organometallic complexes/nanometallic catalyst, which limit its practicality and economy.…”

“…alcohol, glycerol or formic acid) [17,31–33] and more recently, boron reagents [34–35] . Other methods based on reduced sulfur reagents like elemental sulfur, [36–37] dithionite [38] or sulfides [39] are useful for the reduction of nitro group, being particularly convenient for the selective reduction of polynitroarenes. From Green Chemistry point of view, the catalytic hydrogenation have received enormous attention by their improvements compared to Bechmap's reduction; [17] however, this type of strategies presents some drawbacks such as the use of specialized equipment and safety issues related to H 2 storage, the manipulation of flammable hydrogen gas and the use of hazardous reagents and sophisticated organometallic complexes/nanometallic catalyst, which limit its practicality and economy.…”

Four-Component Ring-Opening Reaction of Pyrroles via C–N Bond Cleavage under Multiple Functions of Elemental Sulfur

“…Thioamide H is obtained from G in the presence of base. Finally, reduction of H by elemental sulfur affords the final product 2a …”