An efficient synthesis and antimicrobial activity of N-bridged triazolo[3,4-b]thiadiazine and triazolo[3,4-b]thiadiazole derivatives under microwave irradiation

Microwave synthesis for a new series of triazolo[3,4-b]thiadiazines and triazolo[3,4-b]thiadiazoles was described. Thus, intermolecular cyclization of triazole 1 with ethyl bromoacetate, chloroacetyl chloride or different alpha-bromoketones under both conventional and microwave conditions afforded triazolo[3,4-b]thiadiazine derivatives in a good yield. The best results (reaction time and yield) were obtained from microwave condition. However, triazolo[3,4-b]thiadiazole derivatives were obtained via cyclization of triazole 1 with aryl isothiocyanate, ethyl chloroformate or alpha,alpha-dibromodimedone without catalyst or in the presence of sodium methoxide and triethylamine, respectively. An attempt to synthesize triazolo[3,4-b]thiadiazine derivatives from reaction of compound 1 with a variety of acetamides was failed; the obtained products are S-alkylated triazoles. Triazolo[3,4-b]thiadiazine 9b and triazolo[3,4-b]thiadiazoles 3a,b, 10 and 12, and triazol-3-ylsulfanyl acetamide derivative 14a have significant results against Escherichia coli, Pseudomonas aeruginosa as gm (-ve) bacteria and Staphylococcus aureus, Bacillus subtilis as gm (+ve) bacteria) and Candida albicans and Aspergillus flavus as pathogenic fungi.