Directed lithiation of unprotected pyridinecarboxylic acids: syntheses of halo derivatives

Deprotonation of all isomeric lithium pyridinecarboxylates and subsequent trapping with hexachloroethane or iodine afforded straightforward access to chloro- and iodopyridinecarboxylic acids, respectively. Starting from lithium 5-bromonicotinate, the introduction of an iodine atom at C4 and further halogen migration allowed the potential of this method to be extended to the synthesis of more elaborate derivatives.