Synthesis and Antimicrobial Study of New Fused Thiazolo[3,2-b]triazine, Triazolo[4,3-b]triazine, and 1,2,4-Triazinone Derivatives

6-[2-(Furan-2-yl)ethyl]-3-sulfanylidene-3,4-dihydro-1,2,4-triazin-5(2H)-one (1) reacted with chloroacetone to give S-acetonyl derivative which cyclized in ethanol under reflux to afford 6-[2-(furan-2-yl)-ethyl]-3-methyl-7H-[1,3]thiazolo[3,2-b][1,2,4]triazin-7-one. 2,4-Bis(furan-2-carbonyl)-6-[2-(furan-2-yl)-ethyl]-3-sulfanylidene-3,4-dihydro-1,2,4-triazin-5(2H)-one and 3-amino-6-[2-(furan-2-yl)ethyl]-2-{[6-(2-(furan-2-yl)ethyl)-5-oxo-2,5-dihydro-1,2,4-triazin-3-yl]sulfanyl}-3-methyl-7H-[1,3]thiazolo[3,2-b][1,2,4]-triazin-7-one were prepared by reaction of 1 with furoyl chloride and dibromoacetonitrile, respectively. Compound 1 also reacted with formaldehyde and with formaldehyde and benzylamine to give 2-hydroxymethyl and 2-(benzylaminomethyl) derivatives. The alkylation of 1 with methyl iodide, followed by treatment with hydrazine hydrate, afforded 6-[2-(furan-2-yl)ethyl]-2-hydrazinyl-1,2,4-triazin-5(2H)-one. Reactions of the latter with aromatic aldehydes and formic acid furnished 3-aryl- and 3-unsubstituted 6-[2-(furan-2-yl)ethyl][1,2,4]tri-azolo[4,3-b][1,2,4]triazin-7(1H)-ones, respectively, and triacetyl and tetrabromophthalazinyl derivatives were obtained by reacting hydrazinyltriazinone with acetic anhydride and tetrabromophthalic anhydride. The newly synthesized compounds were evaluated for their antimicrobial activity against some bacterial and fungal strains.