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

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.

Key words

basicity - halogen/metal permutation - isomerizations - organometallic intermediates - solvent effects

References

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6

When treated consecutively with butyllithium and carbon dioxide in tetrahydrofuran at -75 °C, 2-chloro-1,3-difluorobenzene is converted into the 2,6-difluorobenzoic acid (70%).

16

Leroux, F.; Schlosser, M. recent results (2003) to be published.