3.3.4.1 Biaryl Synthesis
The coupling of aryl halides to afford biaryls using copper source is called Ullman reaction. The order of reactivity of aryl halides follows the order: ArI > ArBr > ArCl. Aromatic ring having electron withdrawing groups at ortho position activate, the ring towards coupling reaction. Unsymmetrical biaryls can be prepared by taking two different aryl halides (Scheme 1). The byproducts can be minimized when one aryl halide is very reactive and the other is relatively unreactive. The reaction takes place via oxidative addition followed by reductive elimination.
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Scheme 1 |
Proposed Mechanism |
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Examples: |
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G. Vlad, I. Horvath, J. Org. Chem. 2002, 67, 6550. |
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| C. W. Lai, C. K. Lam, H. K. Lee, T. C. W. Mak, H. N. C. Wong, Org. Lett. 2003, 5, 823. |
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