Unprecedented Strong Lewis Bases - Synthesis and Methyl Cation Affinities of Dimethylamino-Substituted Terpyridines†


A versatile method for the synthesis of functionalized 2,2′:6′,2′′-terpyridines by assembly of the terminal pyridine rings is presented. The cyclization precursors—bis-β-ketoenamides—are prepared from 4-substituted 2,6-pyridinedicarboxylic acids and acetylacetone or its corresponding enamino ketone. Treatment with trimethylsilyl trifluoromethanesulfonate induces a twofold intramolecular condensation providing an efficient access to 4,4′′-di- and 4,4′,4′′-trifunctionalized 6,6′′-dimethyl-2,2′:6′,2′′-terpyridines. Using this method, hitherto unknown 4,4′′-bis(dimethylamino)- and 4,4′,4′′-tris(dimethylamino)terpyridines have been prepared that show remarkably high calculated Lewis basicities.
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