TiCl<sub>2</sub>(OTf)-SiO<sub>2</sub>: A solid stable lewis acid catalyst for Michael addition of α-Aminophosphonates, Amines, Indoles and Pyrrole

<p>TiCl<sub>2</sub>(OTf)-SiO<sub>2</sub> is simply prepared by immobilization of TiCl<sub>3</sub>(OTf) on silica gel surface and introduced as a non-hygroscopic Lewis acid catalyst for C-N and C-C bond formation <i>via</i> Michael addition reaction. A variety of structurally diverse nitrogen nucleophiles including α-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 TiCl<sub>2</sub>(OTf)-SiO<sub>2</sub> as a catalyst. The reactions were conducted at room temperature or 60 °C under solvent-free conditions and the desired Michael adducts were obtained in high to excellent yields.</p> <p></p>