Abstract
Synthesis of new heterocyclic compounds containing four five-membered rings together was the main goal of this work. The new derivatives of [tetrakis (1,2,4-triazole /1,3,4-thiadiazole /1,3,4-oxadiazole][bis-(benzene-1,3,5-triyl)] dioxymethylene A7-A18 were synthesized by the reaction of [bis-(dimethyl 5-yl-isophthalate)] dioxymethylene compound A1 which was previously prepared from the reaction of 1,2-dibromomethan and dimethyl 5-hydroxyisophthalate, then treated with hydrazine hydrate to yield the corresponding acid hydrazide A2. In the next step, compound A2 was refluxed with 4-substituted isothiocyanate to give substituted thiosemicarbazides A3-A6. The treatment of the latter compounds in basic medium of 2M of NaOH afforded 1,2,4-Triazole derivatives A7-A10. Whereas the reaction of the same compounds with concentrated sulfuric acid gave 1,3,4-thiadiazoles A11-A14. Furthermore, the new derivatives of 1,3,4-oxadiazole A15-A18 were obtained by the reaction of thiosemicarbazides and tosyl chloride in presence of pyridine. (C. H. N.) elemental analysis, FT-IR, and 1HNMR techniques were used to characterize the chemical structure of some of the new synthesized compounds which also exhibited an important biological activity.
Highlights
Oxadiazols, thiadiazoles and triazoles are important classes of five-membered heterocycles with three hetero atoms; oxygen, sulfur and nitrogen
A variety of substituted 1,3,4-oxadiazoles have been reported as anticancer, antimicrobial and antiviral materials [10,11,12,13,14,15,16,17]. Due to their wide and extensive range of biological properties, as well as the structural feature as a synthetic intermediate for many pharmaceutical agents, there is a remarkable attraction by all the interested chemists to synthesis and development of new derivatives of fivemembered heterocyclic compounds
By ring closure mechanism, bis-1,3,4-oxadiazole compounds were prepared from an acid hydrazide which was resulted from the reaction of an aromatic ester and hydrazine hydrate [21]
Summary
Oxadiazols, thiadiazoles and triazoles are important classes of five-membered heterocycles with three hetero atoms; oxygen, sulfur and nitrogen. General procedure for the synthesis of [tetrakis(4-substitutedphenylthiosemicarbazide)][bis(benzene-1,3-dicarboxy-5-yl)] dioxymethylene A3-A6: The acid hydrazide compound A2 (2.16 g, 0.005 mol) and appropriate 4-substituted isothiocyanate (0.02 mol) in absolute ethanol (15 ml) were placed in a round bottom flask and refluxed for 3 h. General procedure for the synthesis of [tetrakis(N-(4-substitutedphenyl)-5-mercapto-1,2,4triazole-3-carboxyl][bis(benzene-1,3,5-triyl)] dioxymethylene, A7-A10: In a round bottom flask, a mixture of 0.005 mol of suitable substituted thiosemicarbazide A3-A6 and 2M solution of sodium hydroxide (20 ml) was heated under boiling in water bath for 4h. General procedure for the synthesis of [tetrakis(5-(4-substitutedphenyl)-1,3,4-thiadiazole-2carboxyl)][bis-(benzene-1,3,5-triyl)] dioxymethylene, A11-A14: A mixture of 0.005 mol of different substituted thiosemicarbazide, A3-A6, and 10 ml of concentrated H2SO4 was stirred at 0°C for 3 h., left at room temperature for 4h., poured onto crushed ice. The precipitated solid was filtered off, washed with water, and recrystallized from ethyl acetate. Whereas 1,3,4-oxadiazol derivatives A15-A18 were obtained from the reaction of A3-A6 with tosyl chloride and pyridine in refluxing THF
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