New method of synthesis of benzo[b]furan-2-thiols from 4-(2-hydroxyaryl)-1,2,3-thiadiazoles

Abstract

Derivatives of benzo[b]furan-2-thiols exhibit a biological action [1] and are employed in the organic synthesis [1–7]. Now only unsubstituted benzo[b]-furan2-thiol and several 2-sulfanylbenzo[b]furan-3-aldehydes are known. The benzo[b]furan-2-thiol proper is obtained by the metallation of benzo[b]furan with butyllithiun followed by treating with sulfur and isolating the benzo[b]furan-2-thiol by acidification [1, 4]. 2-Sulfanylbenzo[b]furan-3-aldehydes were prepared from 2-halobenzo[b]furan-3-aldehydes and sodium hydrosulfite [6, 7]. We developed a new method of preparation of both unsubstituted and previously unknown substituted in the aromatic ring benzo[b]furan-2-thiol from easily available 4-(2-hydroxyaryl)-1,2,3-thiadiazoles. The initial 4-(2hydroxyaryl)-1,2,3-thiadiazoles we prepared from 2-hydroxyacetophenones through the corresponding ethoxycarbonylhydrazones with subsequent treatment with thionyl chloride [8]. 4-(2-Hydroxyaryl)-1,2,3-thiadiazoles Ia–Ic under the action of a base, potassium carbonate, in anhydrous DMF decomposed with the nitrogen elimination and the forma-