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

ABSTRACT

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 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 TiCl₂(OTf)-SiO₂ 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.

GRAPHICAL ABSTRACT

KEYWORDS:

• Michael reaction
• titanium(IV) triflate
• α-aminophosphonates
• heterogeneous catalysts
• electron deficient olefins

Acknowledgements

We are grateful to Shiraz University Research Council for support of this work.

Author contribution statement

The data of this manuscript are taken from the corresponding author PhD Thesis, Shiraz University: ‘New applications of trichlorotitanium(IV) trifluoromethanesulfonate, TiCl₃(OTf) & preparation and application of silica bound Ti(IV), TiCl₂(OTf)-SiO₂ as a heterogeneous catalyst in organic transformations'. Professor Habib Firouzabadi: Thesis Director.

Supplementary material

Electronic Supplementary Information (ESI) available: copies of NMR spectra of the new compounds and characterization data of known compounds.