TiCl2(OTf)-SiO2: A solid stable lewis acid catalyst for Michael addition of α-Aminophosphonates, Amines, Indoles and Pyrrole

TiCl2(OTf)-SiO2 is simply prepared by immobilization of TiCl3(OTf) on silica gel surface and introduced as a non-hygroscopic Lewis acid catalyst for C-N and C-C bond formation via Michael addition reaction. A variety of structurally diverse nitrogen nucleophiles including -aminophosphonates, aliphatic and aromatic amines and imidazole were evaluated as Michael donors. Friedel-Crafts alkylation of indoles and pyrrole was also investigated through Michael addition reaction in the presence of TiCl2(OTf)-SiO2 as a catalyst. The reactions were conducted at room temperature or 60 degrees C under solvent-free conditions and the desired Michael adducts were obtained in high to excellent yields. [GRAPHICS]