Transformation of organic compounds by transition metal salts in ionic liquids

Abstract

A new, convenient, and high yielding synthetic protocol for transformation via oxidation process of various organic compounds using a combination of 1-hexyl-3-methylimidazolium bromide ([hmim]Br) and a transition metal salt, such as FeCl3, and CuCl2 is uncovered. The oxidation of alcohols utilizing FeCl3/[hmim]Br in the presence of tert-butyl hydroperoxide (TBHP) afforded the corresponding carbonyl compounds in high yields. Primary and secondary benzylic alcohols seem to be reactive substrates for conversion to the desired carboxylic acids and ketones, respectively, without by-products formed. For aromatization of cyclic dienes catalyzed by CuCl2 coupled with TBHP in [hmim]Br, cyclic hydrocarbons yielded highly amount of the expected aromatic substances under short reaction time, while heterocyclic amines furnished the expected heteroaromatics in moderate yield. Consequently, the developed catalytic system of a transition metal salt/[hmim]Br displayed the reusability in this methodology. For the dehydrogenation of N-heterocycles, FeCl2/DMSO combination under oxygen atmosphere offered the corresponding N-heteroaromatic products in good yields via radical involving process, the catalytic system operated better under conventional organic solvents than ionic liquids.