Controlled anion migrations with a mixed metal Li/K-TMP amide: general application to benzylic metalations.

A general method is described for benzylic metalation of o-, m-, and p-substituted toluenes using a mixed metal amide base generated from BuLi/KOtBu/TMP at -78 °C in THF. The excellent selectivity achieved can be rationalized by the ability of the mixed metal amide base to facilitate an anion migration from the kinetic (o-aryl) to the benzylic metalation site. Remarkably, this controlled anion migration is achievable with catalytic amounts of TMP at -78 °C.