A transfer hydrogenative condensation between 2-nitroanilines and vicinal diols for the synthesis of quinoxalines, with no additional oxidant, reductant and base.
The iron-catalyzed hydrogen transfer strategy has been applied to the redox condensation of o-hydroxynitrobenzene with alcohol, leading to the formation of benzoxazole derivatives. A wide range of 2substituted benzoxazoles were synthesized in good to excellent yields without the addition of an external redox agent. A series of control experiments provided a plausible mechanism. Furthermore, the reaction system was successfully extended to the synthesis of benzothiazoles and benzimidazoles.
Herein, we describe novel iron-catalyzed
transfer hydrogenation
between alcohols and 1-(2-nitrophenyl)pyrroles for the synthesis of
pyrrolo[1,2-α]quinoxalines. The tricarbonyl (η4-cyclopentadienone) iron complex catalyzed the oxidation of alcohols
and the reduction of nitroarenes, and the corresponding aldehydes
and aniline were generated in situ. The resulting
Pictet–Spengler-type annulation/oxidation completed the quinoxaline
structure formation. The protocol tolerated various kinds of functional
groups and provided 29 samples of 4-substituted pyrrolo[1,2-α]quinoxalines.
The developed method was also applied for the synthesis of additional
polyheterocycles.
Benzimidazoles are important N-heteroaromatic compounds with various biological activities and pharmacological applications. Herein, we present the first iron-catalyzed selective synthesis of 1,2-disubstituted benzimidazoles via acceptorless dehydrogenative coupling of primary alcohols with aromatic diamines. The tricarbonyl (η 4-cyclopentadienone) iron complex catalyzed dehydrogenative cyclization, releasing water and hydrogen gas as by-products. The earth abundance and low toxicity of iron metal enable the provision of an eco-friendly and efficient catalytic method for the synthesis of benzimidazoles.
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