ASPECTS OF METALLIC HALIDE-CATALYSED REACTION OF GRIGNARD REAGENTS WITH ORGANIC HALIDES .3. REACTIONS WITH BROMOPYRIDINES

The reactions of aliphatic Grignard reagents with bromopyridines afford low yields of alkylpyridines derived by substitution of the halogen of the bromopyridine by the alkyl group of the Grignard reagent. In the presence of cobalt(II) chloride increased yields result. This is considered to be due to the formation of a co-ordination metal halide complex between the bromopyridine and cobalt(II) chloride, which aids nucleophilic substitution of the halogen of the bromopyridine. A competing reaction is exchange between the Grignard reagent and bromopyridine to afford a pyridylmagnesium halide, which produces pyridine on hydrolysis. Minor products are the phenylpyridines presumed to be formed by substitution by pyridyl radicals, derived from the bromopyridines, in the benzene solvent used as diluent.