Catalytic dehalogenation of halogenated pyridine donors under DOW-phenol conditions

Various halogenated pyridines (2-fluoropyridine, 2-chloropyridine, 2-bromop yridine, 3-bromopyridine, 2,5-dibromopyridine, and 3,5-dibromopyridine) are subject to catalytic reduction and substitution under DOW-phenol condition s; copper(I) benzoate is shown to play a key role in these processes. In th e absence of copper(I), the halogenated pyridines do not react with benzoic acid, while after precipitation of copper(I) halide the dehalogenation pro cess stops, Marked differences are observed between the copper(I)-catalyzed dehalogenation of the halopyridines and the previously reported dehalogena tion of halogenated aromatics. While the copper(I)-catalyzed substitution o f haloaryl compounds by benzoate makes only a minor contribution to the ove rall dehalogenation process, substitution of halopyridine compounds is at l east as important as the reduction reaction. Furthermore, the reaction with halopyridine compounds is regioselective, in contrast to that with halogen ated aryl compounds.