| Abstract: | Refluxing 3-amino-2-iminonaphtho1,2-d]thiazole ( 1 ) with diethyl oxalate ( 2a ) in a 2:1 molar ratio in dry pyridine provided 2,2′-binaphtho1′,2′:4,5]thiazolo3,2-b]1,2,4]triazole ( 3 ). On the other hand, when 1 was treated with excess amount of 2a in dimethylformamide, it afforded ethyl naphtho1′,2′:4,5]thiazolo3,2-b]1,2,4]triazole-2-carboxylate ( 4a ) on heating and ethyl N-(2-iminonaphtho1,2-d]thiazol-3-yl)oxamate ( 5 ) by stirring at room temperature. Cyclization of 5 upon fusion led to the formation of 3-hydroxy-2H-naphtho-1′,2′:4,5]thiazolo3,2-b]1,2,4]triazin-2-one ( 6 ). Compound 6 could also be prepared directly from 1 by refluxing either with 2a neatly, in glacial acetic acid or with oxalic acid ( 2b ) in the same medium. The acid form of 4a might be obtained from 1 and 2b on heating in dimethylformamide, but it was decarboxylated to naphtho-1′,2′:4,5]thiazolo3,2-b]1,2,4]triazole ( 4b ) during the reaction. |
