Synthesis of mono-, bis- and tris-tridentate ligands based on 5′-substituted-2,2′-bipyridine-6-carboxylic acid

The synthesis of 5′-methyl-2,2′-bipyridine-6-carboxylic acid is described starting from the pivotal 5′-methyl-6-bromo-2,2′-bipyridine building block. Functionalisation of the latest at the 5′-methyl position gives access to the 5′-bromomethyl, 5′-hydroxymethyl and 5′-aminomethyl derivatives. Upon nucleophilic substitution, the hydroxy and amino derivatives react with the 5′-bromomethyl compound to give quasi-linear and podand type intermediates. Thanks to a carboalkoxylation reaction at the 6-bromo position of the different intermediates, followed by a saponification reaction, mono-, bis- and tris-tridentate ligands are obtained, which are particularly well suited for the complexation of lanthanide(III) cations.