Room-Temperature Synthesis of Pyrazoles, Diazepines, β-Enaminones, and β-Enamino Esters Using Silica-Supported Sulfuric Acid as a Reusable Catalyst Under Solvent-Free Conditions

Abstract

Silica-supported sulfuric acid (H₂SO₄·SiO₂) has been utilized as a heterogeneous recyclable catalyst for a highly efficient regio- and chemoselective condensation of hydrazines/hydrazides, diamines, and primary amines with various β-dicarbonyl compounds at room temperature to afford pyrazoles, diazepines, and β-enaminones/β-enamino esters under solvent-free conditions within 5–15 min.

Keywords:

• Diazepines
• β-enaminones/β-enamino esters
• H₂SO₄·SiO₂
• heterogeneous recyclable catalyst
• pyrazoles
• solvent-free conditions

Notes

^a Reactions performed with 1.0 mmol of β-dicarbonyl compound, 1.1 mmol of hydrazine/hydrazide, and 20 mg of H₂SO₄·SiO₂ mixed for 5–8 min under solvent-free condition, at room temperature.

^b Isolated yields after column chromatography.

^c Yields of reactions performed in 50°C.

^a Reactions performed with 1.0 mmol of β-dicarbonyl compound, 1.1 mmol of diamine, and 20 mg of H₂SO₄·SiO₂ mixed for 15 min under solvent-free conditions at room temperature.

^b Isolated yields after column chromatography.

^a Reactions performed with 1.0 mmol of β-dicarbonyl compound, 1.1 mmol of primary amines, and 20 mg of H₂SO₄·SiO₂ mixed for 6–12 min under solvent-free conditions at room temperature.

^b Isolated yields after column chromatography.

^c Reactions performed with 2.0 mmol of β-dicarbonyl compound, 1.1 mmol of primary amines, and 20 mg of H₂SO₄·SiO₂ mixed for 6–12 min under solvent-free conditions at room temperature.

^a Reactions performed with 1.0 mmol of pentane-2,4-diketone, 1.1 mmol of aniline, and 20 mg of H₂SO₄·SiO₂ mixed for 7 min under solvent-free condition at room temperature.

^b Isolated yields after column chromatography.