Title:Synthesis of 1,8-Dioxo-octahydro-xanthene and Tetrahydrobenzo[b]pyran
Derivatives Promoted by two Bis-imidazolium-based Ionic Liquids
Volume: 9
Issue: 2
Author(s): Maryam Shirzad, Mitra Nasiri, Nader Daneshvar, Farhad Shirini*Hassan Tajik
Affiliation:
- Department of Chemistry, College of Science, University of Guilan, Rasht, Iran
- Department of Chemistry, University
Campus 2, University of Guilan, Rasht, Iran
Keywords:
Bronsted acidic ionic liquids, bis-imidazolium hydrogen sulfate, bis-imidazolium perchlorate, 1, 8-Dioxo-octyahdro- xanthenes, tetrahydrobenzo[b]pyrans, bis-dicationic ionic liquids.
Abstract:
Aim and Objective: In this work, we have prepared two bis-dicationic ionic liquids with
the same cationic core (Bis-imidazole) and different counter-anions using sulfuric acid and perchloric
acids. After that, the efficiency and ability of these compounds as catalysts were investigated
and compared with respect to the promotion of Knoevenagel condensation and synthesis of benzo[
b] pyran derivatives to see the effect of the anionic counter-part in the reaction.
Materials and Methods: In a 25 mL round-bottomed flask, a mixture of aldehyde (1.0 mmol), 1,3--
cyclo dicarbonyl (2.0 mmol), and the desired amount of the above-mentioned acidic ionic liquids
was heated at 90°C in the absence of solvent (Reaction A). In a 25 mL round-bottomed flask, a
mixture of aldehyde (1.0 mmol), 1,3-cyclo dicarbonyl (1.0 mmol), malononitrile, (1.1 mmol) and
calculated amounts of the ionic liquid in water (3.0 mL) was heated at 80°C (Reaction B) for the appropriated
time. After the completion of the reaction which was monitored by TLC of (n-hexane:
EtOAc; 3:1). 10 mL of water was added and the mixture was stirred for 2 minutes. Then, the products
were separated by filtration and washed several times with water, after drying, the pure products
were obtained.
Results: Comparison of the obtained results from both the ionic liquids revealed that [H2-
Bisim][HSO4]2, because of its more acidic structure, had shown a more catalytic activity in the preparation
of 1,8-dioxo-octahydro-xanthene derivatives but [H2-Bisim][ClO4]2 was relatively more efficient
for the synthesis of tetrahydrobenzo[b]pyran derivatives. Because the stronger acidic nature
of [H2-Bisim][HSO4]2 may prevent the simple activation of malononitrile in the reaction media.
Conclusion: In this study, we have introduced efficient methods for the synthesis of 1,8-dioxo-octahydro-
xanthene and tetrahydrobenzo[b]pyran derivatives in the presence of catalytic amounts of
[H2-Bisim][ClO4]2 and [H2-Bisim][HSO4]2. These methods have several advantages such as ease of
preparation and handling of the catalysts, high reaction rates, excellent yields, eco-friendly procedures,
and simple work-up.
