The palladium-catalyzed cross-coupling reactions of 3-chloro-4-halogeno-1,2,5-thiadiazoles

3,4-Dichloro- and 3-chloro-4-halogeno-1,2,5-thiadiazoles (halogeno-: bromo- and iodo-) are involved in Pd-catalyzed cross-coupling reactions under Stille and Suzuki conditions. As a result, by using the commercially available 3,4-dichloro-1,2,5-thiadiazole as substrate, several 3-alkyl-, 3-alkenyl-, 3-alkynyl-and 3-aryl-4-chloro-1,2,5-thiadiazoles can easily be prepared. However, these reactions through direct desymmetrization of the 3,4-dichloro-1,2,5-thiadiazole always occur with side-reactions resulting from the concurrent decomposition of the heterocyclic ring of the starting material. These problems are resolved by involving, in these Pd-catalyzed cross-coupling reactions, the more reactive and selective 3-bromo-4-chloro- and 3-chloro-4-iodo-1,2,5-thiadiazole. These new dihalogeno-1,2,5-thiadiazoles can easily be prepared, via diazotization reaction followed by halogen substitution, from the 3-amino-4-chloro-1,2,5-thiadiazole.