Cyclocondensation of 3‐amino‐2‐iminonaphtho[1,2‐d]thiazole with oxalic acid derivatives

Abstract

Refluxing 3‐amino‐2‐iminonaphtho[1,2‐d]thiazole (1) with diethyl oxalate (2a) in a 2:1 molar ratio in dry pyridine provided 2,2′‐binaphtho[1′,2′:4,5]thiazolo[3,2‐b][1,2,4]triazole (3). On the other hand, when 1 was treated with excess amount of 2a in dimethylformamide, it afforded ethyl naphtho[1′,2′:4,5]thiazolo[3,2‐b][1,2,4]triazole‐2‐carboxylate (4a) on heating and ethyl N‐(2‐iminonaphtho[1,2‐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]thiazolo[3,2‐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]thiazolo[3,2‐b][1,2,4]triazole (4b) during the reaction.

Synthesis and biological evaluation of 3,6-diaryl-7H-thiazolo[3,2-b] [1,2,4]triazin-7-one derivatives as acetylcholinesterase inhibitors

“…The target compounds 4a-k were obtained by a reaction of compound 3 with substituted phenacyl chlorides in acetic acid. The target compounds 5a-c were prepared with the Williamson reaction shown in Scheme 2 (Ahmad et al, 1987;Liu et al, 1992;Ramadan et al, 2005).…”

Synthesis and biological activity of 3,6-diaryl-7H-thiazolo[3,2-b][1,2,4]triazin-7-one derivatives as novel acetylcholinesterase inhibitors

“…3,6-diaryl-7H-thiazolo[3,2-b][1,2,4]triazin-7-ones 4 were prepared by reaction of 3 with substituted phenacyl chlorides in the presence of acetic acid. Target compounds 5 were obtained using classical Williamson reaction, shown in Scheme 2 [12][13][14].…”