Aromatization of Hantzsch 1,4-Dihydropyridines with Al(NO₃)₃·9H₂O and/or Fe(NO₃)₃·9H₂O in the Presence of Silica Sulfuric Acid Under Mild and Heterogeneous Conditions

Abstract

A simple and convenient method for the aromatization of Hantzsch 1,4-dihydropyridines to the corresponding pyridines is achieved via combination of aluminum or ferric nitrates and silica sulfuric acid as environmentally friendly and novel oxidizing media. This oxidation was carried out in dichloromethane under heterogeneous conditions with good to excellent yields.

Keywords:

• Aluminum nitrate [Al(NO₃)₃·9 H₂O]
• aromatization
• 1,4-dihydropyridines
• ferric nitrate [Fe(NO₃)₃·9 H₂O]
• silica sulfuric acid [SiO₂-OSO₃H]

ACKNOWLEDGMENT

The authors thank the research facilities of Ilam University, Ilam, Iran, for financial support of this research project.

Notes

^a DHP/Fe(NO₃)₃·9H₂O/SiO₂·OSO₃H = 1: 1.5 mmol: 0.2 g.

^b Isolated yield.

^c No reaction.

^d Reaction did not complete.

^a I refers to grams of silica sulfuric acid; II and III refer to mmol of aluminium nitrate and ferric nitrate respectively.

^b Isolated yield. All products were identified by comparison with authentic samples (mp, IR, ¹H NMR, and ¹³C NMR).

^a Isolated yield.