Asymmetric biaryls aryl halide reactions

The Ullmann reaction (Figure 13.4) represents another synthesis of substituted biphenyls. In this process an aryl iodide or—as in the present case—an aryl iodide/aryl chloride mixture is heated with Cu powder. It is presumed that under standard conditions the aryl iodide reacts in situ with Cu to form the aryl copper compound. Usually, the latter couples with the remaining aryl iodide and a symmetric biphenyl is formed. In a few instances it is also possible to generate asymmetric biaryls via a crossed Ullmann reaction. In these cases one employs a mixture of an aryl iodide and another aryl halide (not an iodide ) the other aryl halide must exhibit a higher propensity than the aryl iodide to couple to the arylcopper intermediate. It is presumed that the mechanism of the Ullmann reaction parallels the mechanism of the Cadiot-Chodkiewicz coupling, which we will discuss in Section 13.4. 

Carbonylative Suzuki Cross-Coupling Reactions Carbonyladve Snzuki cross-coupling is a useful SCR (boronic acid + aryl halide + CO) to prepare asymmetric substimted kehmes [70]. One of the main drawbacks of this methodology is the direct couphng reaction, which forms biaryl products without carbon monoxide insertion, particularly with electron-deficient aryl haUdes. 

---