Alkylation of 3-allyl-5,5-dimethyl-2-thioxo-2,3,5,6-tetrahyd-robenzo[h]quinazo-line-4(1H)-one (thioxobenzoquinazoline) was alkylated in an alkaline medium with halides of various structures, resulting in the formation of 2-sulfanylsubstituted 3-allyl-5,5-dimethyl-5,6-dihydrobenzo[h]quinazolin-4(3H)-ones. The condensation of thioxobenzohquinazoline with hydrazine hydrate yielded 3-allyl-2-hydrazinyl-5,5-dimethyl-5,6-dihydroben-zo[h]quinazoline-4(3H)-one. However, analogous reactions with 2-ethanolamine and 3-propanolamine proceeded anomalously, resulting in the formation of 2-(2-hydroxyethyl)amino-5,5-dimethyl-5,6-dihydroben-zo[h]quinazoline-4(3H)-one and 2-(3-hydroxypropyl)amino-5,5-dimethyl-5,6-dihydro-benzo[h]quinazoline-4(3H)-one, respectively. Interaction of the mentioned thioxoben-zohquinazoline with benzylamine occurs through intramolecular cyclization, forming 6,6,10-trimethyl-9,10-dihydro-5H-benzo[h]thiazolo[2,3-b]quinazoline-7(6H)-one. The antibacterial properties of the synthesized compounds were studied against both Gram-positive and Gram-negative microorganisms. The research results revealed that the investigated compounds possess antibacterial activity.