Promoting or Preventing Haloaryllithium Isomerizations: Differential Basicities and Solvent Effects as the Crucial Variables.

SYNTHESIS 2005, No. 4, pp 0617–0621xx.xx.2005 Advanced online publication: 18.01.2005 DOI: 10.1055/s-2005-861787; Art ID: T11504SS © Georg Thieme Verlag Stuttgart · New York Abstract: 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 °C, whereas at –75 °C 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 °C, under conditions that preclude halogen migration, and unleash the isomerization process by adding tetrahydrofuran at –75 °C.