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:

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