N-Aryl-4-hydroxy-6-methyl-2H-pyran-2-one-3-carbothiamides and N-aryl-4-hydroxycoumarin-3-carbothiamides were synthesized by the reaction of arylisothiocyanates with 4-hydroxy-6-methylpyran-2-one and 4-hydroxycoumarin, respectively. Novel products 3-[bis(arylamino)methylene]-6-methyl-2H,4H-pyran-2,4-diones and N,N′-diaryl-4-hydroxycoumarin-3-carboximidamides have also been obtained in the same reactions. Novel 4-acetoacetyl-3-phenylamino-4,5-dihydro-5H-pyrazol-5-ones were synthesized from the reaction of N-aryl-4-hydroxy-6-methyl-2H-pyran-2-one-3-carbothiamides with an excess of hydrazine. The structure of all compounds was established by NMR and mass spectra.