DBU: a highly efficient catalyst for one-pot synthesis of substituted 3,4-dihydropyrano[3,2-c]chromenes, dihydropyrano[4,3-b]pyranes, 2-amino-4H-benzo[h]chromenes and 2-amino-4H benzo[g]chromenes in aqueous medium

A series of easily prepared Lewis basic ionic liquids were developed for cyclic carbonate synthesis from epoxide and carbon dioxide at low pressure without utilization of any organic solvents or additives. Notably, quantitative yields together with excellent selectivity were attained when 1,8-diazabicyclo[5.4.0]undec-7-enium chloride ([HDBU]Cl) was used as a catalyst. Furthermore, the catalyst could be recycled over five times without appreciable loss of catalytic activity. The effects of the catalyst structure and various reaction parameters on the catalytic performance were investigated in detail. This protocol was found to be applicable to a variety of epoxides producing the corresponding cyclic carbonates in high yields and selectivity. Therefore, this solvent-free process thus represents an environmentally friendly example for the catalytic conversion of carbon dioxide into value-added chemicals by employing Lewis basic ionic liquids as catalyst. A possible catalytic cycle for the hydrogen bond-assisted ring-opening of epoxide and activation of carbon dioxide induced by the nucleophilic tertiary nitrogen of the ionic liquid was also proposed.

Lewis Basic Ionic Liquids-Catalyzed Conversion of Carbon Dioxide to Cyclic Carbonates

Highly efficient conversion of carbon dioxide catalyzed by polyethylene glycol-functionalized basic ionic liquids

Ionic Liquids: Applications and Perspectives

Data published in the last 10 years on the use of the aza-Michael reaction in organic synthesis are described systematically. The attention is focused on environmentally friendly processes following green chemistry principles and on methods for the synthesis of compounds that are difficult to access by other routes.

https://iopscience.iop.org/article/10.1070/RC2011v080n03ABEH004162/pdf

Aza-Michael reaction: achievements and prospects

Aza-Michael addition of aliphatic or aromatic amines to α,β-unsaturated compounds catalyzed by a DBU-derived ionic liquid under solvent-free conditions

An efficient, clean and facile protocol for the Knoevenagel condensation of aromatic aldehydes with active methylene compounds catalysed by task specific ionic liquid 1,8-diazabicyclo[5.4.0]-undec-...

Green and efficient Knoevenagel condensation catalysed by a DBU based ionic liquid in water

The DBU (1,8-Diazabicyclo[5.4.0]undec-7-ene) derived task-specific ionic liquids [DBU][Lac] (1,8-diazabicyclo[5.4.0]-undec-7-en-8-ium lactate), [DBU][Ac] (1,8-diazabicyclo[5.4.0]-undec7-en-8-ium acetate) and [DBU][Tfa] (1,8-diazabicyclo[5.4.0]-undec-7-en-8-ium trifluoroacetate) were synthesized. Among the three novel ionic liquids, [DBU][Lac] was found to have the highest catalytic activity for aza-Michael addition of aromatic amines to α,β-unsaturated ketones. The protocol can give good to excellent products yields and has advantages such as readily work-up and good reusability, which makes this method quite attractive.

Green and efficient aza-Michael additions of aromatic amines to α,β-unsaturated ketones catalyzed by DBU based task-specific ionic liquids without solvent

The invention relates to a green efficient method for condensing aromatic aldehydes and active methylene compounds. The method comprises: taking ionic liquid as a catalyst; subjecting aromatic aldehydes and active methylene compounds to catalytic condensation reaction at room temperature under normal pressure; filtering the obtained product to obtain corresponding condensation product water serving as a reaction medium; stirring the obtained product at room temperature; and finishing reaction and then directly filtering the obtained product so as to obtain products. Filtrate containing aqueous phase of the ionic liquid can be repeatedly used ten times as a catalytic reaction system, and reaction yield does not drop. The method has the advantages of simple operation, high yield, good use repeatability of the catalytic reaction system, mild reaction conditions and good prospects for industrialization.

Novel method for condensing aromatic aldehydes and active methylene compounds through catalysis of functional ionic liquid

With the continuing depletion of natural resources and the growing environmental awareness, current and future chemists are being trained to develop synthetic routes in economically beneficial manner. One strategy to realize these green processes in organic synthesis is the replacement of toxic volatile organic solvents with environmentally more benign reaction mediums. Among the novel green solvents that have been reported, ionic liquids (ILs) have been one of the most active areas of green chemistry over the past decade, due to their excellent chemical and thermo properties such as good thermal stability, negligible vapor pressure, ease of handling, potential for recycling, good coordinating and dissolving capability. Thus, ILs were widely used in various organic transformations(Miao & Chan, 2006; Ying et al., 2008; Ying et al., 2008). However, most of the ILs studied by chemists are structurally based on imidazole which is inert for organic reactions. So the need for the developments of novel task-specific ionic liquids still exists. On the other hand, 1,8-diazabicyclo[5.4.0]undec-7-ene(2,3,4,6,7,8,9,10octakydropyrimido [1,2-┙]azep -ine, DBU) was found to be superior to other tertiary amines as catalyst, base or promoter. For example, using DBU as catalyst for Balylis-Hillman reaction and aza-Michael addition was reported by Aggarwal and Kim respectively(Aggarwal & Mereu, 1999; Yeom et al., 2007). DBU-mediated CO2-fixation reaction(Yoshida et al., 2008), DBU-promoted, S-Ntype Smiles and Ireland-Claisen rearrangement reactions(Ma et al., 2007; Li et al., 2007), DBU-catalyzed addition reactions of sulfonylimidates(Matsubara & Kobayashi, 2008), DBUpromoted chemoselective cleavage of acetylenic TMS group(Yeom et al., 2008), and DBUassisted unusual dehydrogenation(Kim et al., 2008) were all found to be very efficient. Considering the special role that DBU played in organic synthesis, ionic liquids with a DBU moisture (Scheme 1) were developed(Tolstikoua & Shainyan, 2006). Because of its large size, low symmetry of cationic moiety and charge delocalization over the N-C=N triad render these type of ionic liquids low melting points. However, the salts in Scheme 1 are inert and can only been used as reaction solvents. Then, we attempted to develop a new class of task-specific DBU-derived ionic liquids which could not only serve as reaction medium but also as catalyst or promotor. The preparation of the five novel ILs can be simply realized by neutralization reaction of DBU and the corresponding carboxyl acids, including acetic acid, lactic acid, propionic acid and butyric acid (Scheme2)(Ying et al., 2009; Ying et al., 2010; Ying, 2010). Among these ILs, [DBU][Tfa]

/pdf/dbu-derived-ionic-liquids-and-their-application-in-organic-4jaa99zzfx.pdf

Anguo Ying

Papers

Aza-Michael addition of aliphatic or aromatic amines to α,β-unsaturated compounds catalyzed by a DBU-derived ionic liquid under solvent-free conditions

Green and efficient Knoevenagel condensation catalysed by a DBU based ionic liquid in water

Green and efficient aza-Michael additions of aromatic amines to α,β-unsaturated ketones catalyzed by DBU based task-specific ionic liquids without solvent

Novel method for condensing aromatic aldehydes and active methylene compounds through catalysis of functional ionic liquid

DBU Derived Ionic Liquids and Their Application in Organic Synthetic Reactions