Homogeneous
catalysts generally show higher catalytic activities,
while heterogeneous catalysts are more easily separated from products.
To combine the advantages of heterogeneous and homogeneous catalysts
has been of great interest for many years. Here, we report a kind
of facilely prepared cross-linked poly(ionic liquid)s (PILs) with
swelling property to increase catalytic activities of heterogeneous
catalysts. The swelling ability of PILs was greatly affected by cross-linking
density and chain length of substituents on imidazolium, and the unique
swelling property prompted the nonporous PILs to contact with substrates
sufficiently, enhancing their catalytic activities similar to homogeneous
ionic liquid monomers.
An effective one‐pot method for the conversion of carbon dioxide, ethylene oxide, and amines to 3‐aryl‐2‐oxazolidinones has been developed. This one‐pot method consists of two parallel reactions and a subsequent cascade reaction between the two products of the corresponding parallel reactions. Notably, the binary ionic liquids of 1‐butyl‐3‐methyl‐imidazolium bromide and 1‐butyl‐3‐methyl‐imidazolium acetate demonstrate a synergistic catalytic effect on this new strategy. 1‐Butyl‐3‐methyl‐imidazolium bromide is essential in two parallel reactions owing to the good nucleophilicity and leaving ability of bromide, and 1‐butyl‐3‐methyl‐imidazolium acetate plays a dominant role in the subsequent cascade reaction owing to the strong basicity of acetate. In addition, the binary ionic liquids can be used thrice without significant loss of catalytic activity.
An intermolecular synergistic catalytic combination of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) and a DBU‐derived bromide ionic liquid has been developed for the conversion of CO2, epoxides, and amines under metal‐ and solvent‐free conditions. Various 3‐aryl‐2‐oxazolidinones are produced in moderate to excellent yields within a short reaction time. NMR spectroscopy and DFT calculations demonstrate that DBU as a hydrogen bond acceptor and the ionic liquid as a hydrogen bond donor activate the substrates cooperatively by inducing hydrogen bonds to promote the reaction effectively. Based on these results, a possible reaction mechanism on the synergistic catalysis of DBU and the ionic liquid is proposed. In addition, the reaction of CS2, ethylene oxide, and aniline catalyzed by the combination of DBU and the DBU‐derived ionic liquid also proceeds smoothly, which opens a hitherto unreported route to [1,3]dithiolan‐2‐ylidenephenylamine in a straightforward way.
We have investigated the reactions of cyclic carbonates/trithiocarbonate and aromatic amines in the presence of a basic ionic liquid, 1butyl-3-methylimidazolium acetate (BmimOAc), which produced various cyclic carbamates/dithiocarbonimidates in fairly good to excellent yields. The use of BmimOAc as catalyst here not only offers an effective approach to the synthesis of the target compounds, but also avoids the use of conventional toxic materials. By means of the reactions of cyclic carbonates and aromatic amines, 3-aryloxazolidin-2-ones, 3,3'-aryldioxazolidin-2-ones and 3-arylA C H T U N G T R E N N U N G [1,3]oxazinan-2-ones could be synthesized. NMR spectroscopy and DFT calculations revealed that both the cation and the anion of BmimOAc activate cooperatively the substrates in these reactions by means of inducing hydrogen bonding. In addition, condensation reactions of ethylene trithiocarbonate and aromatic amines also proceeded very well in the presence of the BmimOAc catalyst, which opened a hitherto unreported route to [1,3]dithiolan-2-ylidene-arylamine derivatives in a straightforward way.
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