Among the large number of compounds of the thieno[2,3-d]pyrimidin-4-one series annelated at both heterocycles, derivatives of type I have been little studied. At the same time, among them are known substances which possess various biological activities (fungicidal, bactericidal, anti-inflammatory, etc.) [3-9], which shows potential for further synthesis and the study of properties of substances with similar structures.The objective of the present work is the synthesis of new derivatives of type I. They are traditionally synthesized from 2-amino-3-ethoxycarbonyl-4,5-disubstituted thiophenes by condensation with lactams [10,11] or O-alkyl esters of lactams [3], and also from cyclic ketones by the Gewald reaction [12,13]. Oxidation [14,15] and formylation [16,17] of such compounds occurs exclusively at the CH 2 group of ring A connected with the heterocyclic system of rings B and C at position 2.