Methylsulfonic Acid Adsorbed on Silica Gel as a Solid Acid for Dimerization of Indoles: A Convenient Synthesis of 2,3′-Bi(3H-indol)-3-one Oximes

Abstract

A simple, convenient, and efficient approach for the synthesis of (E)-2,3′-bi(3H-indol)-3-one oxime derivatives has been developed. The methodology is based on a three-component coupling reaction of indoles and sodium nitrite using a silica-supported methylsulfonic acid as solid acid. The practical utility of this three-component coupling reaction has been demonstrated in the gram-scale dimerization of indole.

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GRAPHICAL ABSTRACT

Keywords:

• Biindoles
• CH₃SO₃H-SiO₂
• indoles
• tandem reaction
• three-component coupling reaction

ACKNOWLEDGMENTS

The authors are grateful to the NSF of China (Nos. 21162001 and 21202023), National Key Technology R&D Program of China (No. 2009BAI78B01), Jiangxi Province Key Support Program (No. 2009BNB06200), Natural Science Foundation of Jiangxi Province (No. 2009GZH0013), and Jiangxi Province Office of Education Support Program (No. GJJ10718) for financial support.

Notes

^a Reaction conditions: indole (0.50 mmol), NaNO₂ (0.60 mmol), rt.

^b Isolated yield.

^c CH₃SO₃H adsorbed on silica.

^d Dicyclohexylamine.

^a Reaction conditions: CH₃SO₃H-SiO₂ (0.55 mmol), indole (0.50 mmol), NaNO₂ (0.60 mmol), pyridine (1 mL), rt.

^b Isolated yield.