ABSTRACT Treatment of 6-methyltetrazolo[1,5-b]-1,2,4-triazine-7-thiol (1) with ethyl bromoacetate yields ethyl sulfanylacetate 2. Reaction of compound 2 with 4-substituted-3-thiosemicarbazides afforded 4-substituted sulfanylacetyl-3-thiosemicarbazides 3a-c. The compounds 3b,c were also prepared via the reaction of 2 with hydrazine hydrate to produce sulfanylacetic acid hydrazide 5 followed by isothiocyanates. Compounds 3a-c were easily cyclized to the corresponding 2-substitutedamino-5-methylsulfanyl-1,3,4-thiadiazole derivatives 6a-c on the treatment with phosphorus oxychloride. The products 6a-c were also synthesized in one-pot cyclization of ester 2 with 4-substituted-3-thiosemicarbazides in the presence of phosphorus oxychloride. Compound 6a was coupled with various aromatic aldehydes to give the corresponding arylideneamino structures 7a-c. Treatment of 1 with 1,2-phenylenediamine resulted compound 8 which cyclized with aromatic carboxylic acids in the presence of phosphorus oxychloride into 7-(2-arylbenzimidazol-1-yl)-6-methyltetrazolo[1,5-b]-1,2,4-triazines 9a-d. Compound 9e was prepared through the reaction of 8 with phenyl iso(thio)- cyanate to obtain isolable anilido intermediates 10 and 11 followed by thermal cyclization. Also, compound 8 underwent ring closure with urea or thiourea to furnish oxo- and thioxobenzimidazolyl structures 13 and 14.
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