Buchwald-Hartwig biphenyl ligands

Independent investigations by Maes and coworkers have involved the use of commercially available and air-stable 2-(dicydohexylphosphanyl)biphenyl (ligand B) as a ligand system for the successful and rapid coupling of (hetero)aryl chlorides with amines under microwave Buchwald-Hartwig conditions (0.5-2 mol% palladium catalyst) [129, 130]. Both methods provide very high yields of products within an irradiation time of 10 min. 

Recently, the limitations for the intermolecular coupling have been significantly mitigated. Kawatsura and Hartwig [14] and Buchwald et al. [15] have demonstrated that aryl bromides and even aryl chlorides react with malonates (Eq. 3) and 1,3-diketones (Eq. 4) by using sterically bulky and electron-rich phosphines, such as P(f-Bu)3, D BPF, and 2-(di-ferf-butylphosphino)-2 -methyl-biphenyl, as ligands. 

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