An interesting synthesis of thieno[2,3-d][1,2,3]thiadiazole via decomposition/recyclization of 3-methoxycarbonyl-¹H-thieno-[2,3- e][1,3,4]thiadiazine 4,4-dioxide

Attempted hydrolysis of the ester of 3-methoxycarbonyl-¹H-thieno[2,3- e][1,3,4]thiadiazine 4,4-dioxide (I) under acidic conditions gave the ring- contracted thieno[2,3-d][1,2,3]thiadiazole (V) instead of the expected carboxylic acid. In addition to a discussion of the reaction, a plausible mechanism is presented.