Fusion of 2-chloro-5- phenyl- 1,3,4-oxa(thia)diazoles (1a,b) with anthrax-nilic acid gave the cyclized compounds 3a,b which on thiation afforded 2-phenyl-1-oxa(thia)-3,3a,9-triaza-cyclopenta[b]naphthalene-4-thiones (4a,b).
Treatment of 1 with 4-chlorophenol and/or 4-chloro-aniline yielded compounds 5a,b and 5c,d, respectively. Condensation of 1a, b with 4-aminoacetophenone yielded 1-[4-(5-phenyl-[1,3,4]oxa(thia)diazol-2-ylamino)-phenyl]-ethanones (6a,b) which on fusion with benzaldehyde afforded the corresponding chalcones7. Reaction of compounds 8a,b and 9a,b, respectively. Refluxing 9 with Ac₂O afforded N-acetylated compounds (10a, b). Reaction of 2-amino-5-phenyl-1,3, 4-oxa(thia)diazoles (11) with acyl bromides afforded 12a-d which on boiling with hydrogen bromide yielded 2,5-diphenylimidazo[2,1-b][1,3,4]oxadiazoles (13a,b).
Fusion of 11a,b with 2-phenyl-4H-3,1-benzoxazin-4-ones afforded 2-phenyl-3-(5-phenyl-[1,3,4]oxa(thia)diazol-2-yl)-3H-quinazolin-4-ones (14a,b). condensation of 11a,b with benzoyl chloride gave 15a,b which on treatment with sodium azide yielded 5-phenyl-1-(5-phenyl-[1,3,4]oxa(thia)diazol-2-yl)-1H-tetrazoles (16a,b). reacting 11a,b with phenylisothio-cyanate gave 17a,b which on condensation with malonic acid afforded 1-phenyl-3-(5-phenyl-[1,3,4]oxa(thia)diazol-2-yl)-2-thioxo-dihydro-pyrimidine-4, 6-diones (18a,b). Some of the compounds have been screened for their fungicidal activity.