Elemental Sulfur Disproportionation in the Redox Condensation Reaction between o‐Halonitrobenzenes and Benzylamines

Abstract

The disproportionation of elemental sulfur at moderate temperatures is investigated in the redox condensation involving o-halonitrobenzenes 1 and benzylamines 2. As a redox moderator, elemental sulfur plays the dual role of both electron donor and acceptor, generating its lowest and highest oxidation states: S(-2) (sulfide equivalent) in benzothiazole 3 and S(+6) (sulfate equivalent) in sulfamate 4, and filling the electron gap of the global redox condensation process. Along with this process, a cascade of reactions of reduction of the nitro group of 1, oxidation of the aminomethyl group of 2, metal-free aromatic halogen substitution, and condensation finally led to 2-arylbenzothiazoles 3.

Octahedral Chiral‐at‐Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions

“…The chiral‐at‐metal catalysts can be synthesized with high enantiomeric purity through a convenient auxiliary‐mediated strategy developed in our laboratory,7 as shown for the synthesis of Λ‐ IrS and Δ‐ IrS in Scheme . Accordingly, IrCl 3 hydrate is reacted with 5‐ tert ‐butyl‐2‐phenylbenzothiazole ( 1 ), synthesized itself in two steps from 1‐bromo‐4‐ tert ‐butylbenzene,12 in 2‐ethoxyethanol/water 3:1 under reflux to provide the iridium dimer complex rac ‐ 2 in a diastereoselective fashion 13. The subsequent reaction with the chiral auxiliary ligand ( S )‐4‐isopropyl‐2‐(2′‐hydroxyphenyl)‐2‐thiazoline (( S )‐ 3 ) affords the iridium(III) complexes Λ‐( S )‐ 4 and Δ‐( S )‐ 4 as a mixture of diastereomers, which can be resolved easily by standard silica gel chromatography on a gram scale 11.…”

Tri‐Functional Elemental Sulfur Enabling Bis‐Heteroannulation of Methyl Ketoximes with Methyl N‐Heteroarenes

“…[6] Consequently, the development of synthetic methods for sulfur-heterocycles has attracted considerable interests in molecular synthesis. [7] In the past decade, cheap, nontoxic and bench-stable elemental sulfur has found versatile functionalities to be an effective moderator to facilitate the formation of nitro-containing heterocycles [8] as well as one of the viable sulfur sources to construct sulfur-heterocycles [9] ( Figure 1a). For example, Nguyen and co-workers have developed a highly atom-economical approach for benzimidazole formation with S 8 as a redox moderator from 2-amino nitrobenzenes and methyl aza-arenes.…”

Cu(NO3)2/Oxone‐Mediated Radical Nitration Cyclization of 1,6‐Enynes

“…Nitro‐compounds are widely applied in pharmaceuticals, materials sciences and fuels . Beyond this, they are also significant intermediates in organic chemistry as the nitro group is easily transformed to amines, sulfamides, amides and heterocycles . Hence, a variety of effective radical nitration strategies, including reaction with alkanes, aromatics, alkenes, alkynes and 1, n ‐enynes, have been developed.…”