The Ullmann reaction uses copper metal to convert aryl halides to biaryl compounds. The mechanism is not yet fully understood, but there are two theories in consideration. The radical mechanism involves a single electron transfer (SET) to form aryl radicals that combine to produce the biaryl product. The second mechanism involves two oxidative additions and an SET to yield a Cu(III) intermediate. Reductive elimination affords the biaryl product.

• Reagents: Cu Metal or Cu(I)-Salts in 1-5 Equiv (e.g. Cu₂O, Cu₂S)
• Reactant: Halogenated Benzene or Heteroaromatic Compound (2 Equiv)
• Product: Symmetrical Biaryl (with Cu-Powder) or Unsymmetrical Biaryl (with Cu(I)-Salt)
• Type of Reaction: Cu-Mediated Coupling

Mechanism

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Related Compounds