Oxidation of thioamide derivatives using superoxide anion and synthesis of benzothiazoles

Abstract

Treatment of N-(2-hydroxyphenyl) benzthioamides with superoxide anion in acetonitril resulted in the formation of 2-substituted benzoxazoles in excellent yields together potassium sulfate. The cyclodesulfurization of N-(2-hydroxyphenyl) benzthioamides appears to involve the formation of peroxysulfer -dioxide or -trioxide like the case of desulfurization of thioamide derivatives. In this cyclization, the combination of a neighbering group effect of a hydroxylate and the leaving group of $SO_NO^-$ (n=1 or 2) seems to play an important role. While, n-benzyl benzthioamide reacted with superoxide anion at 20$^\circ$C resulted in the formation of N-benzoyl benzamide. Benzyl methylene groups of thioamides were found to reacted with a peroxysulfur intermediate which is generated for o-nitrobenzenesulfonyl chloride adn superoxide to give the corresponding carbonyl compounds at 20$^\circ$C in THF Or $CH_3CN$. It was found that N-(2-mercaptophenyl) benzamides reated with $P_2S_5$ in pyridine to afford the 2-substituted benzothiazoles in excellent yields, where $P_2S_5$ appears to be catalyst.