Synthesis and Biological Activities of Some 1,3,4-Oxadiazoles and Bis (1,3,4-Oxadiazoles)

Oxidative cyclization of hydrazones (1) derived from aromatic aldehydes and aroylhydrazines with iodine and yellow mercuric oxide gave 2,5-diaryl-1,3,4-oxadiazoles (2). Condensative cyclization of the same hydrazones by heating with acetic anhydride or benzoyl chloride in the presence of pyridine gave 3-acetyl-2,5- diaryl-2,3-dihydro-1,3,4-oxidiazoles (3) or 3-benzoyl-2,5- diaryl-2,3-dihydro-1,3,4-oxadiazoles (4). Dehydrogenative cyclization of oxalic or adipic acids bis (aroylhydrazides) (5 and 6) gave bis (5-aryl-1,3,4-oxadiazol-2-yl) (7) or 1,4-bis (5-aryl-1,3,4-oxadiazol-2-yl) butane (8). Bis (5-aryl-1,3,4-oxadiazol-2-yl (7) were also prepared by the oxidative cyclization of glyoxal bis (aroylhydrazones) (9). Bis (3-acetyl-5-aryl-2,3-dihydro-1,3,4-oxadiazol-2-yl) and bis (3-benzoyl-5-aryl-2,3-dihydro-1,3,4-oxadiazol-2-yl) derivatives (10 and 11) were obtained by condensative cyclization of glyoxal bis (aroylhydrazones) (9) with acetic anhydride or benzoyl chloride. Nematocidal, insecticidal, and herbicidal activities of some of the prepared compounds are reported.