Cobalt- and Iron-Catalyzed Redox Condensation of o-Substituted Nitrobenzenes with Alkylamines: A Step- and Redox-Economical Synthesis of Diazaheterocycles

Abstract

A wide variety of functionalized 2-aryl benzimidazoles can be prepared by a solvent-free cobalt- or iron-catalyzed redox condensation of 2-nitroanilines and benzylamines. The cascade including benzylamine oxidation, nitro reduction, condensation, and aromatization occurs without any added reducing or oxidizing agent. The method can be extended to other alkylamines as reducing components or 2-nitrobenzamides as oxidizing components when using an iron/sulfur catalyst to afford various diazaheterocycles.

Heterogeneous Palladium‐Catalyzed Hydrogen‐Transfer Cyclization of Nitroacetophenones with Benzylamines: Access to C−N Bonds

“…[2][3][4] Given that nitro compounds are inexpensive and easily available chemical materialsand that their reduction is afundamental and significant transformation in synthesizingv arious nitrogen-containing medicala nd synthetic intermediates, the direct transition-metal-catalyzed oxidative coupling of CÀHb onds with nitroarenes for the construction of CÀNb onds through ah ydrogen-transfer strategy is highly desirable. [5] Additionally, externalo xidants are not involved in this strategy.R ecently, we [6] and others [7] successfully developedahydrogen-transfer strategyf or CÀNb ond construction by using nitroarenes and alcohols (or amines)a st he substrates. However,t hus far,t he application of this strategy in the direct oxidativea minationo f C(sp 3 )ÀHb onds with an itro group through aC ÀNb ond cleavage/formation sequence under heterogeneous catalysis has not been reported.Quinazolinesa nd their derivatives are regarded as an important class of nitrogen-containing heterocycles because of their extensive appearance in natural products and active molecules.…”

Recent Advances in Organic Reactions Involving Elemental Sulfur

“…When another aliphatic alkylamine 658 was used as reducing partner or when o ‐nitrobenzamides 657 were used as oxidizing partners toward primary benzylamines, the Fe–S catalyst generated in situ from FeCl 3 ⋅6 H 2 O and S 8 showed its superior catalytic activity, leading to a wide range of benzimidazole 659 and quinazolinone 660 derivatives (Scheme ) …”

Recent Trends in Iron‐Catalyzed Reactions towards the Synthesis of Nitrogen‐Containing Heterocycles

“…(b) Synthesis of benzimidazoles : A simple and economical solvent‐free redox condensation of 2‐nitroanilines and benzylamines catalyzed by cobalt or iron was developed for the synthesis of benzimidazoles (Scheme ) . The scope of the reaction was extended to other alkylamines in which they functioned as reducing components in the presence of an iron/sulfur catalytic system.…”