The structure of the recyclization products was demonstrated by spectral methods and X-ray structural analysis.Keywords: alkylamines, 1-(alkylamino)phenylmethylidene-3-methylcarbamoyl-4-oxo-1,4-dihydrobenzo [4,5]imidazo[1,2-a]pyridines, 1-alkyl-5-benzoyl-3-ethoxycarbonyl-6-methylthio-1,2-dihydropyridin-2-ones, 3-alkylcarbamoyl-1-benzoyl-4-oxo-4H-benzo[4,5][1,3]thiazolo[3,2-a]pyridines, 3-alkylcarbamoyl-1-benzoyl-4-oxo-4,10-dihydrobenzo [4,5]imidazo[1,2-a]pyridines, 6-alkylcarbamoyl-8-benzoyl-5-oxo-1,2,3,5-tetrahydroimidazo[1,2-a]pyridines, 7-alkylcarbamoyl-9-benzoyl-6-oxo-1,2,3,5-tetrahydro-2H-pyrido[1,2-a]pyrimidines, 1-amino-2-mercaptoethane, 1,3-diaminopropane, o-aminothiophenol, diaminoethane, o-phenylenediamine, recyclization X-ray structural analysis.We showed recently that 1-alkyl-5-benzoyl-3-ethoxycarbonyl-6-methylthio-1,2-dihydropyridin-2-ones 1a,b are regiospecifically cyclocondensed with nitrogen-containing 1,2-, 1,3-, 1,4-, and 1,5-dinucleophiles [1-4]. In the last two cases the reaction proceeds as a recyclization [3,4].The aim of the present work was to establish unequivocally the structure of the products of recyclization, to study the limits of its application, to investigate the effect of the ratio of starting materials on the direction of the reaction, and to clarify the sequence of formation of intermediate compounds.It was discovered that 1-alkyl-5-benzoyl-3-ethoxycarbonyl-6-methylthio-1,2-dihydropyridin-2-ones 1a,b react with an excess of diaminoethane 2a and 1,3-diaminopropane 2b nonselectively. The reaction products are therefore not derivatives of 5-benzoyl-3-heteryl-2H-2-pyranone, as we proposed previously [3,4], but are 6-alkylcarbamoyl-8-benzoyl-5-oxo-1,2,3,5-tetrahydroimidazo[1,2-a]pyridines 3a,b, 7-alkylcarbamoyl-9-benzo-yl-6-oxo-1,2,3,5-tetrahydro-2H-pyrido[1,2-a]pyrimidines 3c,d, and 1-alkyl-6-(1-alkyl-5-benzoyl-