Palladium-Catalyzed Directed Halogenation of Bipyridine N-Oxides
Sina P Zucker1, Friedrich Wossidlo1, Manuela Weber1
1Freie Universität Berlin , Institut für Chemie und Biochemie, Takustrasse 3, 14195 Berlin, Germany.
Abstract:
The palladium-catalyzed directed C-H halogenation of bipyridine N-oxides was investigated. Using NCS or NBS (N-chloro- or N-bromosuccinimide) and 5 mol % Pd(OAc)2 in chlorobenzene (0.10 molar) at 110 °C, pyridine-directed functionalization took place and 3-chloro- or 3-bromobipyridine N-oxides were obtained in high yields. The reaction is sensitive to steric hindrance by 4- and 6'-substituents. Only in the latter case, where coordination of palladium by the pyridine is hindered, 3'-halogenation directed by the N-oxide function was observed. The halogenated products were deoxygenated by PCl3 or PBr3.
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