Synthesis of Novel Thiazolidin-4-ones by Reaction of MalonthioamideDerivatives with Dimethyl Acetylenedicarboxylate.-Reaction of malonothioamides (I) with dimethyl acetylenedicarboxylate (II) stereoselectively affords the novel thiazolidin-4-ones (III) in (E,Z)-geometry which undergo an isomerization of the C(2)-C (8) double bond in polar solvents to furnish the (Z,Z)-isomers (IV). In some cases, where the (E,Z)-isomer cannot be stabilized by intramolecular hydrogen bonding [cf. compounds (V)], the thiazolidinones are obtained as a mixture of (E,Z)-(VI) and (Z,Z)-isomers (VII). -(BERSENEVA, V. S.; TKACHEV, A. V.; MORZHERIN, Y. Y.; DEHAEN, W.; LUYTEN, I.; TOPPET, S.; BAKULEV, V. A.; J.