Diastereoselective Approach to Non-racemic Bipyridine bis-N-Oxides

Significance

The highly diastereoselective iodine-mediated oxidative dimerization of chiral pyridine N-oxides, prepared by metal-halogen exchange from readily available pyridines, is reported. A number of chiral non-racemic bipyridines with axial and central chirality were thus prepared. Although the dependence of selectivity of the reaction on various conditions (solvent, base, oxidizing agent) was studied and mechanistic speculation was provided, the origin of diastereoselectivity remains unclear. As discussed by the authors and precedented in the literature, bipyridine N-oxides may serve as chiral add-ons for various asymmetric reactions.