Reactions of N-phenyl-3-oxobutanethioamide with 3-aryl-2-propenoyl chlorides in acetone in the presence of potassium carbonate give rise to 4-aryl-5-acetyl-1-phenyl-6-thioxopiperidin-2-ones, 2-aryl-5-acetyl-6phenylamino-2,3-dihydro-4H-thiopyran-4-ones, and 6-aryl-2-acetonylidene-3-phenyl-5,6-dihydro-4H-1,3-thiazin-4-ones whose structure was proved both by spectral methods and chemical transformations.

No abstract

Earlier we developed a general method for obtaining condensed heterocycles containing a 1,3-triazine ring, based on the reaction of nitrogen-containing thiones with 3-aryl-2-propenoyl chlorides in pyridine [1][2][3][4]. In this work, we have studied the reaction of 3-oxo-3-R 1 -N-R 2 -propanethioamides 1a-c with 3-aryl-2-propenoyl chlorides 2a-c. Since 3-oxo-3-R 1 -N-R 2 -propanethioamides 1a-c have several reaction centers [5,6], the products of this reaction can be 3,4-dihydro-2H-pyran-2-ones, 4H-pyran-4-ones, 4H-1,3-thiazin-4-ones, 6H-1,3-thiazin-6ones, 4H-thiopyran-4-ones, 2H-thiopyran-2-ones, 4H-piperidin-4-ones, and 6-thioxopiperidin-2-ones, which complicates isolation and identification of the compounds formed.The optimal conditions for carrying out the reaction involve stirring a solution of 3-oxo-3-R 1 -N-R 2propanethioamides 1a-c and 3-aryl-2-propenoyl chlorides 2a-c in acetone in the presence of K 2 CO 3 at 20-50°C for 2.5 h. The products of each reaction, according to TLC and 1 H NMR spectroscopy, are a mixture of two compounds which have the same elemental composition and were separated by treatment of the reaction mixture with a 5% aqueous NaOH solution. Detailed analysis of the 1 H NMR, 13 C NMR, and IR spectra of the reaction products, and also comparison of this information with the spectral data for 4H-thiopyran-4-ones and 4Hpiperidin-4-ones given in [7], showed that as a result of the reaction, 4-aryl-1-aryl(alkyl)-5-acyl-6thioxopiperidin-2-ones 3a-d, 2-aryl-6-aryl(alkyl)amino-5-acyl-2,3-dihydro-4H-thiopyran-4-ones 4a-d, and 2-acetonylidene-6-(4-nitrophenyl)-3-phenyl-5,6-dihydro-4H-1,3-thiazin-4-one (5) were formed.The type of heterocycles, their ratio and yield depend on the nature of the substituents R 1 , R 2 , and Ar 1 in the starting 3-oxo-3-R 1 -N-R 2 -propanethioamides 1a-c and 3-aryl-2-propenoyl chlorides 2a-c. Acylation of 3-oxo-N-phenylbutanethioamide 1a by 3-phenyl-2-propenoyl chloride (2a) and 3-(4-chlorophenyl)-2-propenoyl chloride (2b) leads to formation of 6-thioxopiperidin-2-ones 3a,b and 4H-thiopyran-4-ones 4a,b in 1:1 ratio, the products of condensation of thioamide 1a with 3-(4-nitrophenyl)-2-propenoyl chloride 2c are 6-thioxopiperidin-2-one 3c and 4H-1,3-thiazin-4-one 5, also in an equimolar ratio.