Gomberg-Bachmann reaction
The Gomberg–Bachmann reaction, named for the Ukrainian-American chemist Moses Gomberg and the American chemist Werner Emmanuel Bachmann, is an aryl-aryl coupling reaction via a diazonium salt.
The arene compound 1 (here benzene) is coupled with base with the diazonium salt 2 to the biaryl 3 through an intermediate aryl radical. For example, p-bromobiphenyl may be prepared from 4-bromoaniline and benzene:
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.
One intramolecular variation which gives better results is the Pschorr cyclization:
The group Z can be CH2, CH2CH2, NH and CO (to fluorenone ) to name just a few.
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