Reevaluating 1,3-Thiazolidinone Reports: Deciphering the Authentic 1,3-Thiazolidinone Frameworks via Synthetic and...

Accurate structural determination of heterocyclic scaffolds is essential for medicinal chemistry and drug discovery. In this study, products obtained from three-component reactions of aryl isothiocyanates, dialkyl acetylenedicarboxylates, and hydrazine hydrate, as well as four-component reactions incorporating aldehydes, were carefully re-examined. Previous studies had described these compounds as thiazine derivatives; however, our comprehensive synthetic and spectroscopic investigations demonstrate that they actually correspond to thiazolidinone frameworks. Key evidence was provided by gradient-selected heteronuclear multiple bond correlation (HMBC) and gated ¹³C NMR spectroscopy, which enabled the determination of regioselectivity and stereochemical features. Comparative analysis with reported X-ray crystallographic data further supported our revised assignments. These results resolve inconsistencies in earlier reports and highlight the critical importance of rigorous characterization in multicomponent heterocyclic synthesis. The findings establish a reliable framework for the identification of related heterocycles, thereby offering valuable guidance for future applications in drug-oriented synthesis and the design of bioactive molecules.