Deprotonation of chloropyridines using lithium magnesates

4-Chloropyridine was deprotonated on treatment with 1/3 equiv of the highly coordinated magnesate Bu₃(TMP)MgLi₂ in THF at −10 °C, as evidenced by trapping with I₂. The use of Bu(TMP)₂MgLi in Et₂O allowed the reaction of 2-chloropyridine, giving the 3-functionalized derivative as the main product. Mixtures of 3- and 4-functionalized derivatives were obtained when 2,6-dichloropyridine was involved in the reaction. Performing the reaction on 3-chloropyridine with lithium magnesates in THF, either the 4,4′-dimer or the 4-iodo derivative was formed after quenching by I₂, the former using 1/3 equiv of Bu₂(TMP)MgLi and the latter using 1 equiv of (TMP)₃MgLi. Similar results were observed with 3,5-dichloropyridine, 2,5-dichloropyridine and 3-chloro-2-fluoropyridine. 1,2-Migration of the lithium arylmagnesate formed by deprotonation was proposed to justify the dimers formation.