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Free from the Science Reviews archive: Zinc/ammonium formate: a new facile system for the rapid and selective reduction of oximes to amines

Posted on 1. March, 2018.

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Various oximes, both aldoximes and ketoximes, are selectively reduced to corresponding amines employing low cost zinc dust and ammonium formate despite presence of other functional groups such as halogens, –OH, –OCH3, –COOH, –CN, > C = C < and –CH3.

The conversion of carbonyl derivatives to amines via oximes is a useful transformation in the synthesis of numerous organic compounds and also during the synthesis of compounds which are key intermediates in biosynthesis of many pharmacological important substances. Numerous new reagents have been developed for the reduction of oximes to amines. Though some of these are widely used, still they have limitations based on chemoselectivity and economic considerations.
The heterogeneous catalytic transfer hydrogenation method has proved more effective for reduction of organic compounds
than traditional hydrogenation or other methods of reduction, as it involves mild reaction conditions, easy work-up and a high degree of selectivity. Earlier reports reveal that catalytic transfer hydrogenation of oximes to amines had been achieved with systems like ammonium formate/10% Pd/C, cyclohexene/10% Pd/C,14 but these systems require reaction times as long as 5–10 hours at reflux, expensive catalysts and also offer very low yields. Moreover, stringent precautions must be taken while employing palladium on carbon because of its flammable nature in presence of air.
In this communication, we report a rapid, selective and simple reduction of oximes to corresponding primary amines using low cost zinc dust and ammonium formate or ammonium chloride at reflux temperature as depicted in Scheme 1. Various other functionalities like halogens, –OH, –OCH3, –COOH, –CN, > C = C < and –CH3 are tolerated. Further, we observed that in the case of nitro oximes, the nitro group on the aryl residue underwent reduction to the amine function at room temperature with this system, whereas the oxime function undergoes reduction only at reflux temperature to yield the corresponding diamine.

Read the full article, free, in Journal of Chemical Research, Volume 2003, Number 6, 1 June 2003, pp. 332-333.

Authors: K. Abiraj and D. Channe Gowda*
Department of Studies in Chemistry, University of Mysore, Mysore-570 006, India

Keywords: oximes, catalytic transfer hydrogenation, zinc dust, ammonium formate, amines