Synthesis of Non‐centrosymmetric Dipolar 4,4′‐Bipyridines: Potential Molecular Tectons for Programmed Assembly of Supramolecular Systems

In this report, we describe a modular synthesis approach towards a new series of non-centrosymmetric, dipolar 4,4′-bipyridines bearing 2,6- and 3,5-functionalized pyridyl moieties at the peripheries. Central to our strategy is the selective substitution on only one pyridyl motif that could contain electron-donating (−CH$_3$) or electron-withdrawing (−F, −Cl, −CF$_3$) groups which causes electronic/steric effects on one nitrogen atom in 4,4′-bipyridines. This synthetic protocol was further applied to prepare azo-functionalized (−N=N−) asymmetric bipyridines and non-centrosymmetric 4,4′-bipyridine N-oxide scaffolds, which overcome the synthetic hurdles oxidizing 4,4′-bipyridines to N-monoxides selectively at only one pyridine. Compared to the conventional symmetrical bipyridines, the dipolar non-centrosymmetric molecular tectons pave the way for the realization of non-centrosymmetric supramolecular assemblies because of the difference in the binding energy of the pyridyl nitrogen atoms.