Gomberg–Bachmann reaction
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. 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: 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 CH, CHCH, NH and CO (to fluorenone) to name just a few.