This work shows the possibility of synthesizing previously unknown 5-(4-bromophenyl)-3-((6-amino-2-mercaptopyrimidine)-4-amino)) methylidene-3H-furan-2-one containing a pharmacophore pyrimidine fragment by four-component one-pot reaction of malononitrile as the second methylene active component, thiourea, orthoester and 5-(4-bromophenyl)-3H-furan-2-one, which proceeds under mild conditions during thermal activation of the reaction mixture in isopropyl alcohol. Orthoester, as an electrophilic particle, makes it possible to introduce an additional carbon atom into the structure. The amino component was mercaptodiaminopyrimidine, which is formed in situ during the transformation by the condensation of malononitrile and thiourea. The composition and structure of the product was established using the methods of elemental analysis, IR and complex NMR spectroscopy data. It has been revealed that 5-(4-bromophenyl)-3-((6-amino-2-mercaptopyrimidine)-4-amino))- methylidene)-3Н-furan-2-one in KBr matrix and in solution exists as a mixture Z- and E-enamines, with a predominance of the E-conformer. This is evidenced by the duplication of signals in the 1 H NMR spectrum of the protons of the exocyclic and furan-2-one fragments and doublets of NH-protons. Based on the experimental data obtained, a scheme for the formation of the target system is proposed. It has been found that the reaction can proceed along two equally probable pathways through the ethoxymethylene derivative (path A) or with the formation of an ethoxyimine intermediate (path B).