Palladium catalyzed asymmetric Suzuki–Miyaura coupling reactions to axially chiral biaryl compounds: Chiral ligands and recent advances

• Pd catalyzed asymmetric Suzuki–Miyaura couplings (Pd-ASMC) is a valuable method to axially chiral biaryl compounds.
• Summary of three main categories of relevant chiral auxiliary ligands applied in Pd-ASMC.
• Evaluation of catalytic performance of chiral ligand systems in Pd-ASMC.
• Discussion of the correlation between ligand coordination, catalyst activity and enantioselectivity.
• Perspective on potential for new developments in the field of Pd-ASMC.

Axially chiral biaryls exist widely in bioactive natural products and auxiliary ligands for homogeneous catalysis. The particular spatial arrangement of the two aromatic rings in the specific space determines their unique properties; therefore, how to effectively control their absolute configuration is the key issue. Within the last decade, the synthesis of axially chiral biaryls has been a research topic of great interest. Asymmetric biaryl coupling controlled by chiral palladium catalysts was first reported in 2000 and has greatly advanced the chemistry of transition-metal-catalyzed cross-coupling reactions. Most notably, some novel chiral auxiliary ligands such as ferrocene- or biaryl backbone-containing monophosphine, bisphosphines, bis-hydrazones, hydrazone–phosphines, diene and NHC ligands have been applied to this reaction. At the same time a broad range of aryl electrophiles such as phenols, aryl ethers, esters, carbonates, carbamates, sulfamates, phosphates, phosphoramides, phosphonium salts, and fluorides can now be coupled efficiently with boron reagents to afford functionalized axially chiral biaryl products with good to excellent yields and enantioselectivities in the presence of chiral palladium catalysts. In this review, we would like to summarize three main categories of chiral catalysts with discussion of their advantages and limitation.

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