Sc(OTf)3 is a new type of a Lewis acid that is different from typical Lewis acids such as AlCl3, BF3, SnCl4, etc. While most Lewis acids are decomposed or deactivated in the presence of water, Sc(OTf)3 is stable and works as a Lewis acid in water solutions. Many nitrogen-containing compounds such as imines and hydrazones are also successfully activated by using a small amount of Sc(OTf)3 in both organic and aqueous solvents. In addition, Sc(OTf)3 can be recovered after reactions are completed and can be reused. While lanthanide triflates [Ln(OTf)3] have similar properties, the catalytic activity of Sc(OTf)3 is higher than that of Ln(OTf)3 in several cases.