Functionalization of Highly Substituted 2,2′:6′,2″-Terpyridine Derivatives

On the basis of an easy access to 2,2′:6′,2″‐terpyridine derivatives bearing 6‐ and 6″‐methyl groups, the functionalization of these substituents was investigated. The direct oxidation or bromination of the methyl groups was not feasible on larger scale; however, a two‐step process employing oxidation to the pyridine N‐oxides followed by acetic anhydride promoted rearrangement (Boekelheide reaction) furnished the corresponding terpyridine derivatives with 6‐ and 6″‐acetoxymethyl groups in reasonable overall yields. These are excellent precursors for the synthesis of tetra‐ and pentadentate ligands, as demonstrated by several examples. This approach allowed access to a library of new functionalized 2,2′:6′,2″‐terpyridine derivatives. Diversity is good! By appropriate functionalization, a variety of new 2,2′:6′,2″‐terpyridine derivatives is accessed. Key is the formation of N‐oxides, followed by Boekelheide rearrangement, which allows the preparation of bis(acetoxymethyl)‐substituted compounds.