Sc(OTf)₃: A Highly Efficient and Renewable Catalyst for Michael Addition of Indoles to Nitroolefins in Water

Abstract

A catalytic amount of scandium trifluoromethanesulfonate [Sc(OTf)₃] (2.5 mol%) was used to catalyze the Michael addition of indoles to nitroolefins in water to afford the corresponding 3-alkylated indoles in good to excellent yields. The short reaction times, excellent yields, and renewability of the catalyst are noteworthy.

Keywords:

• Lewis acid
• Michael addition
• renewable catalyst
• scandium trifluoromethanesulfonate
• water

ACKNOWLEDGMENT

We acknowledge the National High Technology Research and Development Program of China (863 Program), No. 2006AA09Z446, for financial support of this work.

Notes

^a All reactions were performed in water at 30 °C.

^b Isolated yield.

^c 1 Equiv 2-cyclopenten-1-one based on β-nitrostyrene was added.

^a All reactions were carried out with 2.5 mol% Sc(OTf)₃ at 30 °C, and were stopped when nitroolefins were consumed.

^b Isolated yield.

^a All reactions were carried out in water at 30 °C.

^b Isolated yield.