The present work deals with the reaction of 4-(4-acetylaminophenyl-4-oxobut-2-enoic acid (1) with sulfur reagents, e.g. thiophenol at different acidity of medium, phenol in the presence of concd. sulfuric acid, and phosphorous pentachloride to afford the corresponding adducts 2-6. Reaction of the latter compounds with different electrophilic and nucleophilic reagents yields some important heterocyclic derivatives