Oxirane-Driven Cascade Transformations of 5-Arylidene-Thiazolidine-2,4-Diones

Abstract

The reaction of thiazolidine-2,4-diones (TZDs) with oxiranes has been thoroughly investigated. For the first time, it has been observed that 5-arylidene-TZD derivatives can undergo transformation into 6-substituted 1,4-oxathian-2-ones. Additionally, it has been demonstrated that certain 3-substituted 5-arylidene-TZDs can convert to 1,4-oxathian-2-ones and oxazolidines upon reaction with oxiranes, confirming that the process follows a cascade mechanism. Several factors have been found to influence the reaction‘s outcome, including the amount of oxirane, the presence of a base, and solvent polarity. It has been determined that dimethylformamide (DMF) is essential for the reaction to proceed efficiently. Furthermore, the critical role of the benzylidene group in facilitating the reaction has been confirmed. An unusual hydrogen bond between the ortho-hydrogens of the phenyl group and the sulfur atom of the thiazolidine ring, observed via NMR spectroscopy, highlights the sulfur atom‘s strong electron-accepting properties, which play a key role in the observed transformations.