title: Lithiation of prochiral 2,2'-dichloro-5,5'-dibromo-4,4'-bipyridine as a tool for the synthesis of chiral polyhalogenated 4,4'-bipyridines.
abstract: Lithiation of the achiral tetrahalogenated 4,4'-bipyridine 1 with alkyllithiums was investigated. n-BuLi was found to induce either the chlorine-directed deprotolithiation reaction alone or with a concomitant halogen-lithium exchange furnishing after iodine trapping chiral 4,4'-bipyridines 2 and 6, respectively. The role of n-BuLi in the deprotolithiation process of 1 was elucidated on the basis of isolated secondary derivatives. After deprotolithiation, the lithiated species could be trapped by different electrophiles such as MeI, TMSCl, MeSSMe, R3SnCl (R = Me or n-Bu), and PPh2Cl. Moreover, 4,4'-bipyridine 2 was submitted to cross-coupling reactions (Suzuki and Sonogashira) which occurred selectively at the carbon-iodine bond. All compounds of this new family of atropisomeric 4,4'-bipyridines were separated by chiral HPLC (high-performance liquid chromatography), and the absolute configurations of obtained enantiomers were mainly assigned by XRD (X-ray diffraction) using anomalous dispersion.
authors.affiliation: Laboratoire SRSMC UMR CNRS 7565, Université de Lorraine, 54506 Vandoeuvre-les-Nancy, France. victor.mamane@univ-lorraine.fr
authors.forename: Victor
authors.initials: V
authors.lastname: Mamane
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Aubert
authors.forename: Paola
authors.initials: P
authors.lastname: Peluso
authors.forename: Sergio
authors.initials: S
authors.lastname: Cossu
mesh_terms: D015394:Molecular Structure; D011725:Pyridines / Q000138:chemical synthesis* / Q000737:chemistry*
chemical_list: C586496:2,2'-dichloro-5,5'-dibromo-4,4'-bipyridine; D011725:Pyridines; C034306:4,4'-bipyridyl