Abstract Bromination of naphtho [1, 2-c][1, 2, 5] thiadiazole (I) gives either an addition product, 4, 5-dibromo-4, 5-dihydronaphtho [1, 2-c][1, 2, 5] thiadiazole (II), or a substitution product, 5, 6-dibromonaphtho [1, 2-c][1, 2, 5] thiadiazole (III), depending on the reaction conditions. Dehydrobromination of II gives 5-bromonaphtho [12-c][1, 2, 5] thiadiazole (IV). Chlorination of I gives the corresponding addition product V or 5-chloronaphtho [1, 2-c][1, ...