Named after Fritz Ullmann Organic Chemistry Portal ullmann-reaction | Reaction type Coupling reaction | |
 | ||
The Ullmann condensation or Ullmann ether synthesis is a variation of the Ullmann reaction, in which a phenol is coupled to an aryl halide to create a diaryl ether in the presence of a copper compound, named after Fritz Ullmann. The corresponding aniline or aryl amide reaction is sometimes called Goldberg reaction, named after Irma Goldberg.
Contents
An example is the synthesis of p-nitrophenyl phenyl ether
An active copper powder that is required for this reaction can be prepared by the reduction of copper sulfate by zinc metal in hot water causing the precipitation of elemental copper.
The reaction often requires high-boiling polar solvents such as N-methylpyrrolidone, nitrobenzene or dimethylformamide and high temperatures (often in excess of 210 °C) with stoichiometric amounts of copper. The aryl halide is activated by electron-withdrawing groups or carries a carboxylic acid group in the aromatic ortho position. The research field was revitalized with the introduction of catalytic copper reactions in 2001–2003 using up to 0.1 equivalent copper iodide, base and a diamine ligand.
Goldberg reaction
An example of a Goldberg reaction is the synthesis of fenamic acid, an intermediate of acridone via the Goldberg reaction:
An Ullmann-type aromatic amination reaction between an aryl iodide and an aryl amine as coupling partners has been published. The catalyst used is formed from copper(I) iodide and phenanthroline. As this reaction proceeds well with an electron-rich aryl iodide it is a valuable alternative to the Buchwald–Hartwig amination reaction, which gives best yields with electron-poor aryl halides.
The scope is extended to amides for example in the synthesis of this Camps cyclization precursor:
Hurtley reaction
The nucleophile can also be carbon as in a carbanion in the Hurtley reaction.
In the original scope the arene was 2-bromobenzoic acid, the carbon nucleophile a malonic ester and other dicarbonyl compounds and the base sodium ethoxide.