The reaction of dimethyl acetylenedicarboxylate with thioureas was re-investigated to examine the structure of the products previously recorded in several papers without definite evidence. By chemical reactions and spectroscopic data the five-membered structure, 2- imino-4-thiazolidone (II), was given to the products, contrary to the previously proposed six- membered structure, 2, 3-dihydro-1, 3-thiazin-4-one.
![2-[3-METHYL-2-(METHYLIMINO)-4-OXO-1,3-THIAZOLAN-5-YL]ACETIC ACID Structure](https://image.chemsrc.com/caspic/327/41306-29-0.png)