Oxidation of thioamide and hydrazone derivativesusing superoxide anio

Abstract

Thioamide derivatives react with superoxide anion to convert to the corresponding amides. When the reaction of thioamides with potassium superoxide was carried out in anhydrous dimethyl sulfoxide, desulfurization of thioamide was slow even at 70$^\circ$C. However, in contrast to the desulfurization in dimethyl sulfoxide, the same reaction in tetrahydrofuran or acetonitrile afforded the corresponding amides in good yields under mild condition. The desulfurization appears to be initiated via the formation of peroxysulfur intermediate. While N,N``-dibenzyldithiooxamide reacted with superoxide anion to give N,N``-dibenzoyldithiooxamide as major product, together with small amount of N,N``-dibenzylthiodioxamide. The model compound, N,N``-di( -methylbenzyl)dithiooxamide can not convert to the corresponding diketone at benzyl moiety like the case of N,N``-dibenzyldithiooxamide probably due to the blocking with methyl group at the carbon attached to the nitrogen. Treatment of N-(2-hydroxyphenyl)-N``-phenylthioureas with superoxide anion at 20$^\circ$C in acetonitrile or in dimethylsulfoxide resulted in the formation of 2-substituted aminobenzoxazoles in excellent yields together potassium sulfate. The cyclodesulfurization of N-(2-hydroxyphenyl)-N``-phenylthioureas appears to involve the formation of peroxysulfur-dioxide or -trioxide like the case of desulfurization of thioamide derivatives. In this cyclization, the combination of a neighboring group effect of a hydroxylate and the leaving group of $SO_4O^-$ (n = 1 or 2) seems to play an important role. Oxidation of tosylhydrazone and hydrazone derivatives with peroxysulfur intermediate which is resulted from the o-nitrobenzenesulfonyl chloride and potassium superoxide afforded the corresponding carbonyl compounds in mostly quantitative yields under mild conditions. The oxidation of tosylhydrazones appears to be initiated by the epoxidation of imino double bond of the substrate. The oxaziridine prepared by o-nitrobenzen...