An Improved Synthesis of 1,3- and 1,4-Bis[5-aryl-1,3,4-oxadiazol-2-,y1]benzenes via Oxidation of Bis-aroylhydrazones of Iso- and Terephthalaldehyde with Lead(IV) Acetate

Synthesis and antibacterial activity of some novel bis-1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles and bis-4-thiazolidinone derivatives from terephthalic dihydrazide

“…Its 1 H NMR spectrum revealed a multiplet at d 7.7-7.9 due to aromatic protons. Physical and spectral data of these compounds are in good agreement with those reported in the literature [31].…”

Unexpected Formation of N-(1-(2-Aryl-hydrazono)isoindolin-2-yl)benzamides and Their Conversion into 1,2-(Bis-1,3,4-oxadiazol-2-yl)benzenes

“…Generally, closure of the 1,3,4-oxadiazole ring has been described , either through intramolecular dehydration ,− of diacylhydrazines or oxidative cyclization − of N -acyl- N ′-arylidene-hydrazines. Numerous dehydrating and oxidative reagents were reported to be very effective for this purpose including phosphorus oxychloride ,, and thionyl chloride .…”

“…Numerous dehydrating and oxidative reagents were reported to be very effective for this purpose including phosphorus oxychloride ,, and thionyl chloride . Recently, triflic anhydride, zirconium(IV) chloride, or [Et 2 NSF 2 ]BF 4 have been mostly used for dehydration, while cerium ammonium nitrate (CAN), lead(IV) tetracetate, − or hypervalent iodine reagents − were reported for the oxidative cyclization. Mixtures of acetic anhydride and acetic acid were also used for the synthesis of dihydrooxadiazoles…”

“…Bis-1,3,4-oxadiazoles could be easily prepared using both synthetic strategies, starting from a wide variety of scaffolds. Most commonly, the heterocycles are generated on different aromatic rings such as in compounds 1 and 2 or as 1,3- or 1,4-subtituted compounds of type 3 or 4 (Scheme ). , Early research describes preparation of bis-1,3,4-oxadiazoles of type 3 (Scheme ) by cyclization with lead(IV) acetate of the corresponding bis-aroylhydrazones derived from 1,3- and 1,4-phthalaldehydes, respectively. The attempt to obtain the 1,2-(bis-oxadiazolyl)benzenes derived from ortho -bis-aroylhydrazones was reported to fail under the same conditions .…”

Syntheses of [1,2,3]selenadiazolo[4,5‐e]benzofuran or benzothiophene, [1,2,3]thiadiazolo[4,5‐e]benzofuran or benzothiophene, and 2‐benzofuranyl‐1,3,4‐oxodiazole derivatives

“…The attempted cyclization of 6a-d with bromine in glacial acetic acid containing anhydrous sodium acetate according to the literature [16], did not give the expected 1,3,4-oxadiazoles 8a-d but rather gave predominately the arylaldehyde 5,7-dibromo-4-hydroxy-3-methylbenzofuran-2-carboxy hydrazones 7a-d. In addition, refluxing 4-hydroxybenzofurans 6a-d with lead tetraacetate in glacial acetic acid [17] resulted in decomposition of the starting material. However the reaction of 4-methoxybenzofurans 6e-l under the latter condition gave the desired 1,3,4-oxadiazoles 8e-l in good yield.…”