Gomberg–Bachmann reaction

{{Short description|Aryl-aryl coupling reaction via a diazonium salt}}

{{Reactionbox

|Name = Gomberg–Bachmann reaction

|Type = Coupling reaction

|NamedAfter = Moses Gomberg
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.{{cite journal | title = The Synthesis of Biaryl Compounds by Means of the Diazo Reaction | journal = J. Am. Chem. Soc. | year = 1924 | volume = 42 | pages = 2339–2343 | doi = 10.1021/ja01675a026 | issue = 10 | last2 = Bachmann | first2=W. E. | authorlink2 = Werner Emmanuel Bachmann | first1 = M. | last1 = Gomberg | authorlink1 = Moses Gomberg}}W. Pötsch. Lexikon bedeutender Chemiker (VEB Bibliographisches Institut Leipzig, 1989) ({{ISBN|3817110553}}){{March6th}}

:Image:Gomberg-Bachmann_reaction.svg

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:{{OrgSynth | prep = cv1p0113 | collvol = 1 | collvolpages = 113 | author1 = M. Gomberg | author2 = W. E. Bachmann | year = 1928 | volume = 8 | pages = 42 |doi = 10.15227/orgsyn.008.0042 | title = p-Bromobiphenyl}}

: 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,{{cite journal | author = J. R. Beadle, S. H. Korzeniowski, D .E. Rosenberg, B. J. Garcia-Slanga, G. W. Gokel | journal = J. Org. Chem. | year = 1984 | volume = 49 | pages = 1594–603 | doi = 10.1021/jo00183a021 | title = Phase-transfer-catalyzed Gomberg-Bachmann synthesis of unsymmetrical biarenes: a survey of catalysts and substrates | issue = 9| last2 = Korzeniowski | last3 = Rosenberg | last4 = Garcia-Slanga | last5 = Gokel}} another is to use 1-aryl-3,3-dialkyltriazenes.{{cite journal | author = T. B. Patrick, R. P. Willaredt, D. J. DeGonia | journal = J. Org. Chem. | year = 1985 | volume = 50 | pages = 2232–2235 | doi = 10.1021/jo00213a007 | title = Synthesis of biaryls from aryltriazenes | issue = 13}}