MW-assisted treatment of oximinoacetanilides obtained from substituted primary aromatic amines was carried out in conc. H 2 SO 4 medium for 5-10 sec to give cyclic amides (isatins) through intramolecular cyclization by means of electrophilic aromatic substitution. Isatins reacted with thiosemicarbazide under MW-condition gave the corresponding Schiff-bases. The Schiff-bases undergo cyclization in presence of minimal Ac 2 O under MW-irradiation for 3-4 min to give the spiro-thiadiazoline acetyl derivatives in excellent yield.