Electrochemical Synthesis of (Hetero)aryl Nitriles

Electrochemical Synthesis of (Hetero)aryl Nitriles

Author: ChemistryViews

Aryl or heteroaryl nitriles can be useful intermediates in organic synthesis and are also found, e.g., in natural products or agrochemicals. Methods for their synthesis are, thus, interesting research targets. α-Imino-oxy acids (example pictured above on the left), a type of oxime ether, can undergo transformations into the corresponding iminyl radicals (R2C=N). Such iminyl radicals can be useful for the synthesis of different nitrogen-containing compounds.

Jing-Mei Huang, South China University of Technology, Guangzhou, China, and colleagues have developed a method for  the electrochemical oxidative decarboxylation of α-imino-oxy acids to give (hetero)aryl nitriles via iminyl radicals (overall reaction pictured). The team first prepared different α-imino-oxy acids from indoles via 1H-indole-3-carbaldehyde intermediates. These aldehydes were reacted with 2-(aminooxy)-2-methylpropanoic acid hydrochloride to give the desired substrates.

The resulting α-imino-oxy acids were then subjected to electrolysis in an undivided cell with a reticulated vitreous carbon (RVC) anode, a platinum cathode, tetrabutylammonium acetate (TBAOAc) as the electrolyte, and a mixture of methanol and acetonitrile as the solvent. The corresponding nitriles were obtained in moderate to excellent yields. Both electron-donating and electron-withdrawing substituents on the indole rings are tolerated. The team demonstrated the usefulness of the method with a one-pot, gram-scale conversion of 1-methyl-1H-indole-3-carbaldehyde to the corresponding nitrile.


 

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