The direct two step synthesis of three new 2-hydrazono-4-oxo-5-thiazolidineacetic acids from thiosemicarbazide, the appropriate ketones (acetophenone, cyclopentanone, cyclohexanone) and maleic anhydride is described. The prepared acids were transformed, via their mixed anhydrides with ethyl carbonate, into their alkylamides in a one-pot procedure.