Comparison of the efficiency of two imidazole-based dicationic ionic liquids as the catalysts in the synthesis of pyran derivatives and Knoevenagel condensations

Abstract

In the present work, 3,3′-(butane-1,4-diyl)bis(1-methyl-1H-imidazol-3-ium) dichloride ([C 4 (MIm) 2 ]•2Cl) and 3,3 ′ -(butane-1,4-diyl)bis(1-methyl-1H-imidazol-3-ium) hydrogen sulfate ([C 4 (MIm) 2 ]•2HSO 4 ) were prepared via adequate, solvent-free methods and characterized using FT-IR, 1 H NMR, 13 C NMR, and potentiometric titration techniques. These reagents were investigated in the synthesis of 5-arylidene (thio)barbituric acids, 2-arylidene malononitriles, 4H-pyrans, and pyrano[2,3d] pyrimidineones, and their catalytic activities were compared in the promotion of these reactions. Based on the obtained results, we found that [C 4 (MIm) 2 ]•2Cl showed more catalytic efficiency where a basic or weak acidic media is needed. In contrast, [C 4 (MIm) 2 ]•2HSO 4 is a powerful catalyst in reactions needing acidic catalysts to enhance the reaction rate. Using these reagents, the products were formed under mild and eco-friendly conditions in excellent yields during short reaction times without needing column chromatography for work-up. Keywords Imidazole-based dicationic ionic liquids • [C 4 (MIm) 2 ]•2Cl • [C 4 (MIm) 2 ]•2HSO 4 • Knoevenagel condensation • 4H-pyrans • Pyrano[23-d] pyrimidineones

Small Heterocyclic D‐π‐D‐π‐A Push‐Pull Molecules with Complex Electron Donors

“…All target chromophores 1-4 except 2 d [41] are new compounds. However, several structural analogues with a different N-alkyl thiobarbituric unit are known; namely analogues of 1 a-e, [58][59][60][61] 2 a, 2 c, 2 d, [34,40,[62][63][64] 3 a, [62,65] and 4 a, 4 c. [40,[62][63][64]66] The preparations and characterizations of new aldehydes 7 c, 7 e, and 8 e are given in the SI. The starting aldehydes 5 a-e, 6 a, 7 a, and 8 a as well as N,N'dibutyl-2-thiobarbituric acid (DBTBA) are commercially available.…”

“…All target chromophores 1 – 4 except 2 d [41] are new compounds. However, several structural analogues with a different N ‐alkyl thiobarbituric unit are known; namely analogues of 1 a – e , [58–61] 2 a , 2 c , 2 d , [34,40,62–64] 3 a , [62,65] and 4 a , 4 c [40,62–64,66] . The preparations and characterizations of new aldehydes 7 c , 7 e , and 8 e are given in the SI.…”

Recent Advances in Imidazolium-Based Dicationic Ionic Liquids as Organocatalysts: A Mini-Review

“…Later, the same authors synthesized two N -methyl imidazolium-based DILs ( Figure 4 ) with the aim to catalyze similar reactions, represented in Scheme 6 [ 35 ].…”

“… DILs catalyzed of 5-arylidene (thio)barbituric acids ( A ), pyrano[2,3- d ] pyrimidinone derivatives ( B ), 2-arylidene malononitriles ( C ), and 4 H -pyrans ( D ), adapted from [ 35 ]. …”

Recent Advances in the Chemistry of Isocyanides with Activated Methylene Group

“…[39,40] Such properties of imidazole and its derivatives draw attention of chemists developing number of approaches toward them. [41] Imidazole-based compounds are also extensively used as organic catalyst, [42,43] dyes [44] and fluorescence biomarkers. [45]…”