Disubstituted thiosemicarbazides reacted with dimethyl acetylenedicarboxylate with formation of
(2-hydrazono-4-oxothiazolidin-5-ylidene)acetates and, in one case, a (2-imino-1,3,4-thiadiazin-5-on-6-
ylidene)acetate. Several mechanistic options involving nucleophilic interaction are presented. The structures
of all newly synthesized compounds were identified by 1H NMR, 13C NMR, COSY, HMQC and HMBC
spectral data.