A convenient method for library construction in liquid phase, which is based on lanthanide triflate (Ln(OTf)(3))-catalyzed three-component reactions, has been developed. Equimolar amounts of each component, an aldehyde, an amine, and a silyl enol ether or an alkene, react smoothly in the presence of Ln(OTf)(3), and the work-up and purification processes are performed by simply passing through a short column. The key is to use Ln(OTf)(3) as a Lewis acid catalyst, which is not decomposed during the work-up and purification steps, and is easily separated from products by the simple procedure. According to this method, various high-quality beta-amino ester and quinoline derivatives have been prepared in parallel in large quantities.