Synthesis of Polyhalogenated 4,4′-Bipyridines via a Simple Dimerization Procedure AbboudMohamed MamaneVictor AubertEmmanuel LecomteClaude FortYves 2010 Polyhalogenated 4,4′-bipyridines were conveniently synthesized in a single step starting from dihalopyridines. A mechanism was proposed on the basis of experiments performed with 2-chloro-5-bromopyridine <b>1a</b>. 2-Chloro-4-lithio-5-bromopyridine <b>A1</b> was produced via ortholithiation of <b>1a</b> by using either LDA or <i>t</i>-BuLi bases. When LDA was used, dimer <b>3a</b> containing two chlorines and two bromine atoms was formed predominantly accompanied by several byproducts whose structure and mechanism of formation are discussed. In the case of <i>t</i>-BuLi, although the major product was 2-chloropyridine <b>7</b>, a new pyridone product <b>8</b> was formed that is probably the result of the dihydropyridine intermediate hydrolysis. The dimerization procedure involving LDA was employed to prepare a large number of halogenated 4,4′-bipyridines in moderate to good yields. In some specific cases, halogenated 3,4′ and 2,4′-bipyridines were obtained in lower yields and their structures were unambiguously assigned by X-ray diffraction analysis.