The previously described 6,8-dibromo-2-(3,4-dichlorophenyl)quinazolin-4(3H)-one 1 was created and employed as a building block for the synthesis of quinazolinone derivatives 2–11 with considerable predicted medicinal activity. The reaction of the hydrazinyl derivative 9 with carbon disulfide led to the 7,9-dibromo-5-(3,4-dichlorophenyl)-[1,2,4]triazolo[4,3-c]quinazoline-3(2H)-thione 12. From the compound 6,8-dibromo-2-(3,4-dichlorophenyl)quinazoline-4(3H)-thione 8 came the quinazolinone derivatives 13–16. Physical and chemical methods were used to characterize constructed products.