Thiazolidines, ring chain tautomerism

Without additional reagents Reactions with thiazolidines Ring-chain tautomerism 4-Thiazolidones from thiazolidines... 

Thiazolidines (76) undergo facile ring-chain tautomerism, thus affording a latent source of thiol-imine, which can be trapped with ethyl mercapto-acetate at 100°-110° to afford 77 in low yield [Eq. (22)].63 If the corresponding acid is used and water is continuously removed, the yield of 77 approaches 75%. 

The ring-chain tautomerism of 1,3-thiazolidines and 1,3-benzothiazolines can be considered as a reversible intramolecular addition to the C=N bond. The system highly prefers the ring form (27a) and only in some cases the open-chain tautomer (27b) can detected (Equation (4)). 

The hydrazinolysis of thiazolidine-2,4-dione (327) and its sulphur analogues generally yields 1,2,4-triazolones (336) by a /m/ij-cyclization process. The isolation of intermediates of type (333) supports the mechanism outlined in the reaction scheme. These intermediates, which are capable of undergoing ring-chain tautomerism [(333) (335)], may be... 

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