Magnesium perchlorate as efficient Lewis acid for the Knoevenagel condensation between β-diketones and aldehydes

Designing highly efficient solvents for the Knoevenagel condensation: two novel dicationic dimethyl phosphate ionic liquids

“…Despite the lack of a basic site 28 in the cation after quaternization, the DIL 5 consequently provided excellent conversion (97% after 60 min) of the aldehyde 6. Although the conversion of 4-(dimethylamino)benzaldehyde (6) in the medium of ILs 3-5 is similar, our attempts to clarify the suitability of dicationic dimethyl phosphate ILs for the Knoevenagel condensation have resulted in the development of two previously unreported compounds. Since DILs usually have enhanced chemical and physical properties 14,15 and decreased toxicity 16 in comparison to monocationic ILs, these new DILs might be a subject of interest in the context of environmentally friendly organic synthesis that benefit from the structural peculiarities of these ILs.…”

“…1 This aspect has aroused a particular interest in developing new and advantageous synthetic approaches towards this reaction. Different molecular solvents, 2 catalysts (organic bases, 3,4 heterogeneous catalysts, 5 Lewis acids 6 ) and reaction conditions (microwave 7 or ultrasound 8 irradiation) have been applied to ensure sufficiently high yields of the target products. Nevertheless, the utilization of toxic solvents or catalysts and prolonged reaction times are inconsistent with the principles of green and sustainable chemistry 9 and still have to be overcome.…”

DBU Derived Ionic Liquids and Their Application in Organic Synthetic Reactions

“…Generally, Knoevenagel reactions are carried out by condensation of active methylene compounds with aldehydes using some organic bases with their salts as catalysts, including dimethylamino pyridine, piperidine, guanidine, ethylenediamine (Narsaiah et al, 2004;Han et al, 2008), and so on. Also, alternative protocols for Knoevenagel condensations catalyzed by Lewis acids such as ZnCl 2 (Shanthan Rao & Venkataratnam, 1991), CuCl 2 (Attanasi et al, 1983), TiCl 4 (Green et al, 1985), LaCl 3 (Narsaiah & Nagaiah, 2003), Mg(ClO 4 ) 2 (Bartoli et al, 2008) and various heterogeneous solid bases, including Zeolites (Saravanamurugan et al, 2006;Martns et al, 2008), sulfate-ion promoted Zirconia , clay (Bigi et al, 1999), and layered double hydroxides (LDHs) (Kantam et al, 2006) have been reported in literatures. However, many of those procedures required the use of large amount of organic solvents as reaction medium, long reaction time, harsh reaction conditions and had difficulties in the reuse of catalysts, which prompt chemical researchers for further development of more environmentally benign, efficient and operationally simple Knoevenagel protocols.…”

A Systematic Study on Knoevenagel Reaction and Nazarov Cyclization of Less Reactive Carbonyl Compounds Using Rare Earth Triflates and Its Applications

“…[1][2][3][4] Identification of diethylamine as a catalyst, first by Knoevenagel,5 paved way for the development of a large number catalysts, [6][7][8][9][10][11][12][13][14][15][16][17][18] and conditions. 19 and MgBr 2 34 are known as LA catalysts.…”

“…Some of these LAs need to be used in more than stoichiometric quantity 35 and catalyst like Mg(ClO 4 ) 2 needs MgSO 4 as additive. 18 The presence of adventitious water as well as water generated during the course of the reaction generally degrades some of these conventional LAs, and renders it non reusable one and leads to generation of pollutants. In almost all of the LA mediated Knoevenagel condensations, only highly reactive carbonyl compounds such as malanonitrile, cyanoacetates and malonates are used as substrates.…”