DABCO as a mild and efficient catalytic system for the synthesis of highly substituted imidazoles via multi-component condensation strategy

Co(II) anchored glutaraldehyde crosslinked magnetic chitosan nanoparticles (MCS) for synthesis of 2,4,5‐trisubstituted and 1,2,4,5‐tetrasubstituted imidazoles

“…[21] 90 min 88 [30] 720-900 min 92 [28] 540 min 90 [26] 55 min 96 [31] 20 min 94 [32] 30 min 80 [27] 12 h 90 [63] 120 min 95 [33] 240 min 81 [29] 45 min 87 [60] 4b [26] 120 min 93 [33] 35 min 76 [27] 720-900 min 86 [32] 240 min 70 [29] 5a MCS-GT@Co(II)/EtOH, refluxing (5 mg) SiO 2 -cl/solvent free, 80°C (250 mg) DABCO/t-BuOH (10 ml), 60-65°C (0.7 mol%) DBSA/H 2 O, refluxing (20 mol%) PEG-400/110°C (1.5 g) Nano-crystalline sulfated zirconia (SZ)/EtOH/refluxing (25 mg)…”

“…This work 40 min 78 [27] 720-900 min 82 [28] 240 min 81 [29] 240 min 86 [30] 45 min 87 [60] SCHEME 4 Proposed mechanism of the reaction …”

“…[25] A variety of catalysts have been reported for the synthesis of multisubstituted imidazoles. [19,21,[26][27][28][29][30][31][32][33] Many of these methods suffer disadvantages like harsh reaction conditions, difficult work-up procedure with large amount of toxic waste generated, use of expensive catalysts and reagents, separation of catalyst from reaction mixture, low yield of product, prolonged reaction time, moisture-sensitive catalyst, high temperature conditions, occurrence of side reactions leading to the formation of side products (including reversed aldol condensation and oxazole formation), lack of generality, in some cases use of more than one step for the formation of product, and strongly acidic conditions. So the development of a simple, clean, efficient, high-yielding, environmentally friendly approach to the formation of products with recyclable and reusable catalysts is still desirable and much in demand.…”

Nano Copper Ferrite Catalyzed Sonochemical, One-Pot Three and Four Component Synthesis of Poly Substituted Imidazoles

“…In the same way several methods have been reported for the synthesis of tetra substituted imidazoles by cyclo condensation of 1,2 dicarbonyl compounds, various aromatic aldehydes, ammonium acetate and aromatic/aliphatic amines using various catalysts such as nano TiCl 4 •SiO 2 [26] [33] as catalyst under Ultra sound irradiation. In extension with these procedures, several methods have been reported for the synthesis of both tri and tetra substituted imidazoels using various catalysts such as molecular Iodine [34], Sodium dihydrogen phosphate [35], BiCl 3 [36], DABCO [37] According to the literature survey, several synthetic protocols have been reported for the synthesis of substituted imidazoles using various type of copper containing catalyst such as synthesis of imidazoles through the Cu 2 O catalyzed cross-cycloaddition between two different isocyanides [43], Synthesis of 1,2,4-trisubstituted imidazoles through the CuCl 2 -catalyzed oxidative diamination of terminal alkynes by amidines [44], Synthesis of multi substituted imidazoles via CuI-catalyzed [3 + 2] cycloadditions [45]. The above reported methods have its own importance and merits, however most of these methods require harmful catalysts, and difficult work-up and effluent pollution.…”

BF3/nano-sawdust as a green, biodegradable and inexpensive catalyst for one-pot synthesis of tri-substituted imidazoles under solvent free conditions

“…The majority of synthetic routes rely on one-pot condensation of diketones or -hydroxyketones with an aldehyde and ammonium acetate in the presence of catalysts such as silica gel or zeolite [9], alumina [10], molecular iodine [11], neutral ionic liquid [12], L-Proline [13], nano-crystalline Sulfated Zirconia (SZ) [14], DABCO [15], AcOH [16], zeolitesupported reagents [17], silica sulfuric acid [18], PEG-400 [19], InF 3 [20], nanocrystalline magnesium ox- [24], and bioglycerol-based carbon catalyst [25]. Some of these catalysts are ideal choices for the synthesis of 2,4,5-tri-substituted imidazoles and are often used for this purpose.…”