Synthesis of 5,6-dihydro[1,2,3]thiadiazolo[5,4-e]-[1,4]oxazepin-8(4)-one

Abstract

Nucleophilic substitution in 5-halo-1,2,3-thiadiazoles is a convenient method for the synthesis of various heterocycles [1,2]. We have previously shown that such reactions may be accompanied by rearrangement of the thiadiazole ring and reactions at C(4) of the ring [3,4]. In a continuation of our studies, we have developed a simple preparative method for the synthesis of a previously unreported heterocyclic system, namely, [1,2,3]thiadiazolo[5,4-e][1,4]oxazepine by the reaction of the ethyl ester of 5-chloro-1,2,3-thiadiazole-5-carboxylic acid (1) [5] with diethanolamine. This reaction involves nucleophilic substitution of the chlorine atom followed by intramolecular transesterification to give heterocycle 2. In contrast to the reaction indicated above, the reaction of thiadiazole 1 with monoethanolamine leads to the Dimroth rearrangement product [6], 5-mercapto-1,2,3-triazole 3, which reacts with starting 5-chloro-1,2,3-triazole 1 under the reaction conditions to give sulfide 4.