Starting material 2-amino-5-(benzthiazol-21-yl-thiomethyl)-1, 3, 4-thiadiazole (1) have been synthesized from easily available 2-carboxymethyl thio benzthiazole, thiosemicarbazide and phosphorous oxychloride. Compound (1) reacts with arylaldehyde and methanol gives 2-arylamino-5-(benthiazol-21-yl-thiomethyl)-1, 3, 4-thiadiazole (2 a-g) were reacts with monochloroacetyl chloride and triethyl amine in dioxin to give 2-azetidinones (3 a-g). Compounds (2 a-g) were reacts with mercapto propionic acid / mercapto acetic acid to give 4-thiazolidinones (4 a-n). Compound (1) reacts with 2-phenyl-4-arylidene -5-oxazolone refluxed in pyridine to give 5-imidazolinones (5 a-g). Antifungal activity has been comparied with Dithane M-45, commercial fungicides, for their fungitoxic action against Phytophthora infestans and Collectotricum falcatum and the results correlated with their structural features.