Design and application of linked-BINOL chiral ligands in bifunctional asymmetric catalysis

The design and application of linked-BINOLs investigated in our group are reviewed. Linked-BINOLs are a kind of semi-crown ether, thus they are flexible and applicable to metals having various ionic radii (Ga3+, Li+, Zn2+, In3+, La3+, and Y3+). The flexible linker segment, containing a coordinative heteroatom, has a crucial role in the construction of a unique and effective chiral environment that is not accessible from BINOL itself. Applications of linked-BINOLs to an epoxide opening reaction, Michael reactions, a direct aldol reaction, direct Michael reactions of a hydroxyketone, and direct Mannich-type reactions of hydroxyketones and N-acylpyrrole are described.