Lanthanide Triflate-Catalyzed Carbon-Carbon Bond-Forming Reactions in Organic Synthesis

Abstract

Versatile carbon-carbon bond-forming reactions using lanthanide triflates (Ln(OTf)3) as catalysts are discussed. Lanthanide triflates are new types of Lewis acids different from typical Lewis acids such as AlCl3, BF3, SnCl4, etc. While most Lewis acids are decomposed or deactivated in the presence of water, lanthanide triflates are stable and works as Lewis acids in water solutions. Many nitrogen-containing compounds such as imines and hydrazones are also successfully activated by using a small amount of Ln(OTf)3. Lanthanide triflates are also excellent Lewis acid catalysts in organic solvents. A catalytic amount of Ln(OTf)3 is enough to complete reactions in most cases. In addition, Ln(OTf)3 can be recovered after reactions are completed and can be reused. Several chiral lanthanide catalysts for asymmetric Diels-Alder, aza Diels-Alder, and 1,3-dipolar cycloaddition reactions are also described.