Preparation of some new 1,3,4-thiadiazine and 1,3,4-oxadiazole derivatives

The reaction between salicylaldehyde and ethyl chloroacetate in DMF formed ester ethyl benzofuran-2- carboxylate 2, followed by the treatment with hydrazine hydrate to afford benzofuran-2-carbohydrazide 3, with carbon disulfide, potassium hydroxide and hydrazine hydrate formed 4-amino-5-(benzofuran-2-yl)-1,2,4- triazole-3-thiol 4a which existed in the mixture of two tautomers (thiol form 4a and thione form 4b).