Dual behavior of monothiocarbohydrazones in the cyclization with diethyl acetylene dicarboxylate (DEAD): synthesis of substituted 1,3-thiazolidin-4-ones

Aliphatic aldehydes and cyclohexanone reacted with thiocarbohydrazide to give exclusively 6-substituted-1,2,4,5-tetrazinane-3-thiones, which readily underwent cyclization with diethyl acetylene dicarboxylate to afford condensed thiazolidinones. On the other hand, cyclopentanone and cycloheptanone reacted under a similar sequence of reaction conditions to give 3-amino thiazolidin-4-ones. [GRAPHICS] .