1.3.4- Thiadiazole, 2-bromo synthesis

The pronounced electron-withdrawing nature of the 1,2,5-thiadiazole system is also evidenced by strong carbonyl electrophilic activation and by enhancement of carboxy acidity. The acid dissociation constants of thiadiazole acids, discussed in Section 4.09.4.1, fall in the range 1.5-2.5. The 1,2,3-thiadiazole carboxylic acids are easily decarboxylated at 160-200 °C. This reaction has been used for the synthesis of monosubstituted derivatives as well as the parent ring and deuterated derivatives <68AHC(9)107>. An efficient bromo-decarboxylation of 3-amino-1,2,5-thiadiazole-carboxylic acid has also been reported <70BRP1190359>. 

A symmetrical tricyclic 1,3,6-thiadiazepine derivative 152 (Scheme 48) has been synthesized [68,69] in 54% yield starting from 5-bromo-thiadiazole derivative 144 and 1,2-diaminobenzene 145. The synthesis embraces two types of molecular rearrangements Smiles and Dimroth s. 

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