Reacting 5-phenyl-1, 3, 4-oxa(thia)diazole-2(3H)-thiones 1 with formaldehyde afforded the corresponding 3-hydroxmethyl derivatives 2 which on condensation with DEM and/or EAA gave 3 and 4, respectively. Treatment of 1 with maleic acid afforded the diacids 5 which on reacting with Ac₂O gave the anhydrides 6. Esterification of 6 with MeOH and PhOH afforded the corresponding esters 7 and 8. Hydrazinolysis of 7 yielded 9 and 10. Treatment of 1 with p-benzoqunone, cyanogen bromide and phenacyl bromide afforded 11, 12 and 13, respectively.
Thiation of 13 with P₂S₅ afforded 14. Reacting 1 with chloroacetyl chloride yielded 15 which on treatment with NH₃ afforded the amide 16.  Condensation of 1 with hydrazine hydrate afforded 17 which on treatment with phenacyl bromide gave 18. Cyclization of 18 with Ac₂O yielded 19. Treatment of 1 with phenylhydrazine gave 20 which on reacting with phenacyl bromide afforded 21. Some of the products were evaluated for their antibacterial activities.