Promoting or preventing haloaryllithium isomerizations: differential basicities and solvent effects as the crucial variables

Deprotonation-triggered heavy halogen migrations should become a favorite tool in arene synthesis if their occurrence and outcome could be made predictable. Particularly attractive, though extremely rare, are stop-and-go situations where a first intermediate, generated by metalation, can be trapped at -100 DegC, whereas at -75 DegC halogen migration gives rise to an isomer. As shown now, one can conveniently produce the initial aryllithium species by halogen/metal interconversion in toluene at -100 DegC, under conditions that preclude halogen migration, and unleash the isomerization process by adding THF at -75 DegC. [on SciFinder (R)]