- Ullmann reaction
The Ullmann reaction or Ullmann coupling [cite journal
title = The Ullmann Synthesis of Biaryls
author = P.E. Fanta
journal = Synthesis
volume = 1974
issue =
pages = 9–21
year = 1974
url =
doi = 10.1055/s-1974-23219 ] is acoupling reaction betweenaryl halide s withcopper . The reaction is named afterFritz Ullmann . [cite journal
title = Ueber Synthesen in der Biphenylreihe
author = F. Ullmann, Jean Bielecki
journal =Chemische Berichte
volume = 34
issue = 2
pages = 2174–2185
year = 1901
url =
doi = 10.1002/cber.190103402141 ]A typical example is the coupling of o-chloro
nitrobenzene to 2,2'-dinitrobiphenyl with a copper - bronzealloy . [ Reynold C. Fuson and E. A. Cleveland, "2,2'-dinitrobiphenyl", "Organic Syntheses ", Coll. Vol. 3, 339. [http://www.orgsyn.org/orgsyn/prep.asp?prep=cv3p0339 Online article] ]The traditional version of the Ullmann reaction requires harsh reaction conditions, and the reaction has a reputation for erratic yields. Since its discovery some improvements and alternative procedures have been introduced. [cite journal
title = Aryl-Aryl Bond Formation One Century after the Discovery of the Ullmann Reaction
author = J. Hassan, M. Sevignon, C. Gozzi, E. Schulz, M. Lemaire
journal =Chemical Reviews
volume = 102
issue =
pages = 1359–1470
year = 2002
url =
doi = 10.1002/cber.190103402141 ]The
reaction mechanism of the Ullmann reaction is extensively studied.Electron spin resonance rules out a radical intermediate. Theoxidative addition / reductive elimination sequence observed withpalladium catalysts is unlikely forcopper because copper(III) is rarely observed. The reaction probably involves the formation of anorganocopper compound (RCuX) which reacts with the other aryl reactant in anucleophilic aromatic substitution . Alternative mechanisms do exist such as σ-bondmetathesis [Derek van Allen, PhD Thesis,University of Massachusetts at Amherst 2004. [http://www.people.umass.edu/dv/group/pdf/dvathesis.pdf Electronic thesis] ] .The Ullmann reaction is limited to electron deficient aryl halides and requires harsh reaction conditions. In
organic synthesis this reaction is often replaced by palladium coupling reactions such as theHeck reaction , theHiyama coupling and theSonogashira coupling In a variation of the Ullmann reaction, 2-
bromo vinyl styrene is reacted withimidazole in anionic liquid to an "n"-vinylimidazole. [Zhiming Wang, Weiliang Bao and Yong Jiang, "L-Proline promoted Ullmann-type reaction of vinyl bromides with imidazoles in ionic liquids", "Chemical Communications", 2005, 2849-51 [http://www.rsc.org/publishing/journals/CC/article.asp?doi=b501628b Abstract] ] [BMIMBF4 stands for theionic liquid 1-Butyl-3-methylimidazolium tetrafluoroborate] The reaction requires "(L)"-prolinecatalysis .References
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