FIELD: organic chemistry, chemical technology, medicine, pharmacy. SUBSTANCE: invention relates to method of synthesis of 1,3-disubstituted 4-oxocyclic ureas used as antifibrillary and anti-arrhythmic agents of the general formula: 
where R1, R2, R3 are taken independently among group comprising of H, Cl, F, Br, NH2, NO2, COOH, CH3SO2NH, SO3H, OH, alkoxy-group, alkyl, alkoxycarbonyl, hydroxyalkyl and acylhydroxy-group; R4 is taken among group comprising of substituted or unsubstituted alkyl, alkenyl, alkynyl, alkylacyl and heteroaryl; and A means substituted or unsubstituted, saturated or unsaturated, linear or branched alkyl- or alkenylamino-group comprising 1-7 carbon atoms; or A means substituted or unsubstituted, saturated or unsaturated heterocycle comprising 5, 6 or 7 members comprising at least one nitrogen atom, and R4 is bound to this nitrogen atom. Method involves the following stages: a) interaction of 1-substituted 4-oxocyclic urea of the formula: 
with reagent comprising carbon chain and taken among 1-bromo-4-chlorobutane, 1,4-dichlorobutane, 1,4-dibromobutane and their mixtures in the presence of weak base taken among group comprising potassium carbonate, sodium carbonate, potassium hydrocarbonate, sodium hydrocarbonate and polar aprotonic solvent to form 3-N-alkylated 2,4- imidazolidinedione; and b) interaction of indicated crude 3-N-alkylated 2,4-imidazolidinedione with amine to form 1,3-disubstituted 4-ococyclic urea. EFFECT: improved method of synthesis, increased yield, enhanced purity of product. 11 cl
