Tributylmagnesium ate complex-mediated novel bromine–magnesium exchange reaction for selective monosubstitution of dibromoarenes

Lithium tributylmagnesate complex (n-Bu3MgLi), readily prepared from n-BuLi and n-BuMgCl (2:1), is a novel metallation agent. It is quite efficient for the selective mono-bromine–magnesium exchange of 2,6-dibromopyridine (1) under non-cryogenic conditions (at −10°C) to give a stable magnesate intermediate. Subsequent treatment with DMF gave 6-bromo-2-formylpyridine (3) in excellent yield. This method is also applicable for selective monosubstitution of several other kinds of dibromoarenes.