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Gomberg–Bachmann reaction

Aryl-aryl coupling reaction via a diazonium salt

Aryl-aryl coupling reaction via a diazonium salt

Werner Emmanuel Bachmann The Gomberg–Bachmann reaction, named for the Russian-American chemist Moses Gomberg and the American chemist Werner Emmanuel Bachmann, is an aryl-aryl coupling reaction via a diazonium salt.

:[[Image:Gomberg-Bachmann_reaction.svg|490px|Gomberg-Bachmann reaction]]

The arene compound (here benzene) is reacted with a diazonium salt in the presence of a base to provide the biaryl through an intermediate aryl radical. For example, p-bromobiphenyl may be prepared from 4-bromoaniline and benzene:

: BrC6H4NH2 + C6H6 → BrC6H4−C6H5

The reaction offers a wide scope for both diazonium component and arene component but yields are generally low following the original procedure (less than 40%), given the many side-reactions of diazonium salts. Several improvements have been suggested. One possibility is to employ diazonium tetrafluoroborates in arene solvent together with a phase-transfer catalyst, another is to use 1-aryl-3,3-dialkyltriazenes.

Pschorr reaction

One intramolecular variation which gives better results is the Pschorr cyclization:

:[[Image:PschorrReaction.svg|Pschorr reaction]]

The group Z can be CH2, CH2CH2, NH and CO (to fluorenone) to name just a few.

References

References

  1. (1924). "The Synthesis of Biaryl Compounds by Means of the Diazo Reaction". [[J. Am. Chem. Soc.]].
  2. W. Pötsch. ''Lexikon bedeutender Chemiker'' (VEB Bibliographisches Institut Leipzig, 1989) ({{ISBN. 3817110553)
  3. {{March6th
  4. (1928). "''p''-Bromobiphenyl".
  5. J. R. Beadle, S. H. Korzeniowski, D .E. Rosenberg, B. J. Garcia-Slanga, G. W. Gokel. (1984). "Phase-transfer-catalyzed Gomberg-Bachmann synthesis of unsymmetrical biarenes: a survey of catalysts and substrates". [[J. Org. Chem.]].
  6. T. B. Patrick, R. P. Willaredt, D. J. DeGonia. (1985). "Synthesis of biaryls from aryltriazenes". [[J. Org. Chem.]].
  7. Pschorr, Robert. (1896). "Neue Synthese des Phenanthrens und seiner Derivate". [[Chem. Ber.]].
  8. {{JerryMarch
  9. (2009). "The Pschorr Reaction, a Fresh Look at a Classical Transformation". [[Current Organic Synthesis]].
  10. (2001). "Sandmeyer reactions. Part 5.1 Estimation of the rates of 1,5-aryl/aryl radical translocation and cyclisation during Pschorr fluorenone synthesis with a comparative analysis of reaction energetics". [[J. Chem. Soc., Perkin Trans. 2]].
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