To industrially advantageously obtain the subject compound useful as an organic intermediate and an intermediate for medicines and agrochemicals by reacting a specific 1,2,5-thiadiazole derivative with an organotin reactant in the presence of a palladium compound catalyst.

A 1,2,5-thiadiazole derivative of formula I [R1 is H, a 1-6C alkyl which may be substituted with (F or a 1-3C alkoxy group) or phenyl which may be substituted with (F, Cl, trifluoromethyl, a 1-6C alkyl or a 1-3C alkoxy); X is Cl or CF3SO3] (e.g. 3-chloro-4-phenyl-1,2,5-thiadiazole) is reacted with an organotin reactant of formula II [R2 is phenyl which may be substituted with (F, Cl, CF3, a 1-6C alkyl or a 1-3C alkoxy)] [e.g. tributyl(4-chlorophenyl)tin, etc.] in the presence of a palladium compound [e.g. tetrakis(triphenylphosphine) palladium to give the objective 1,2,5-thiadiazole derivative of formula III.