Alkynylation of halo pyrimidines under Pd/C–copper catalysis: regioselective synthesis of 4- and 5-alkynylpyrimidines

5-Bromo-4-chloro-6-methylpyrimidines underwent facile Pd/C–Cu catalyzed coupling reactions with a variety of terminal alkynes, which resulted in the corresponding 4-alkynyl-5-bromopyrimidines, regioselectively, with good yields. 4-Chloro-5-iodo-6-methylpyrimidine, however, yielded the corresponding 5-alkynyl-4-chloropyrimidines under the same reaction conditions.