Efficient Solvent-Free Knoevenagel Condensation Between β-Diketone and Aldehyde Catalyzed by Silica Sulfuric Acid

Abstract

Silica sulfuric acid has been utilized as an efficient heterogeneous recyclable catalyst for Knoevenagel condensation between poorly reactive β-diketones and aldehydes under solvent-free conditions. This protocol also works well with more reactive β-ketoesters. The condensation is efficient, clean, and mild. The scope and generality of the Knoevenagel condensation were investigated. The procedure led only to the Knoevenagel product, and no side product derived from a subsequent Michael addition of β-diketone to alkene was detected at rt. Increasing temperature led to a subsequent Michael addition, and it was applied to the efficient synthesis of 9-aryl-1,8-dioxo-octahydroxanthene derivatives.

Keywords:

• 9-Aryl-1,8-dioxo-octahydroxanthene derivatives
• Knoevenagel condensation
• silica sulfuric acid

ACKNOWLEDGMENTS

The authors thank NNSF of China (No. 20972142), the State Key Laboratory of Bio-organic and Natural Products Chemistry, The Chinese Academy of Sciences (No. 08417), the Natural Science Project of Henan Province (2009A150030, 082300420110), and the Innovation Fund of Zhengzhou University (2008CXSY147) for financial support.

Notes

^a Isolated yield.

^b The ratio found from ¹H NMR.

^a Isolated yield.