Synthesis of 2-Indolyl-1-nitroalkane Derivatives Using Nanocrystalline Titanium(IV) Oxide

Abstract

The catalytic Friedel–Crafts alkylation of indoles with nitroalkenes to furnish 2-indolyl-1-nitroalkane derivatives at room temperature with moderate to excellent yields is reported using nanocrystalline titanium(IV) oxide (nano-TiO₂) catalyst. In all cases, a single regioisomer was obtained. After completion of the reaction, the catalyst was recovered by centrifugation and activated under a nitrogen flow for 1 h at 250°C for further reuse. The nano-TiO₂ can be reused for four cycles with a slight decrease of activity under the same reaction conditions.

Keywords:

• Friedel–Crafts alkylation
• heterogeneous catalysis
• 2-indolyl-1-nitroalkane
• nanocrystalline titanium(IV) oxide

ACKNOWLEDGMENTS

S. L. and J. Y. thank the Council of Scientific and Industrial Research, New Delhi, and P. S. thanks the University Grants Commission, New Delhi, for the award of research fellowships. Nanocrystalline metal oxide samples were obtained from Nanoscale Materials Inc., Manhattan, Kansas, USA.

Notes

^a Reaction conditions: indole (1 mmol), trans-β-nitrostyrene (1 mmol), catalyst (10 mol%), solvent (4 mL), room temperature.

^b Isolated yields.

^a Reaction conditions: indole (1 mmol), trans-β-nitrostyrene (1 mmol), nano-TiO₂ (10 mol%), DCM (4 mL), room temperature.

^b Isolated yields.

^a Reaction conditions: indole (1 mmol), nitroalkenes (1 mmol), nano-TiO₂ (10 mol%), DCM (4 mL), room temperature.

^b Isolated yields.

^c The diastereoisomeric ratio was 7:3 and was determined by ¹H NMR on the crude product.