Ionic imidazolium-tagged catalysts

To evaluate a real effect of the pyridinium function in terms of activity and recyclability, we then prepared the complex 16. This pyridinium-containing catalyst, equivalent to 14a, possesses the same C3 alkyl linker between the ionic tag and the benzenylidene pattern. The direct comparison between the imidazolium-tagged catalyst 14a, and its pyridinium-containing equivalent 16 showed similar conversions and reuses over six cycles (Figure 8, entry 3). 

The catalyst leaching problem could be solved by incorporating an ionic tag onto the 4-hydroxyproline [82]. In teres lirigly, the imidazolium-tagged organo-... 

Another comparative study of the CM reaction catalyzed by a second generation Grubbs carbene complex (without imidazolium tag) has been recently presented by Tang and coworkers [264]. They compared the catalytic transformation of styrene in [BMIM][BF4] and [BMIM PFs] with the same reaction in CH2Q2 (3 h, 45 °C) and obtained comparable yields of the CM product in all solvents in the first cycle. In the case of the two ionic liquids the product was extracted with diethyl ether and the remaining ionic catalyst solution could be recycled four times with only a small drop in catalytic activity (product yield 75% in the fourth cycle compared to 85% in the first cycle in [BMIMjfPFs]). The scope of the study also included the successful... 

The Biginelli multi-component synthesis of 5-acyl dihydropyrimidin(thi)ones (117, X = S or O) from a (thio)urea, [H2N-C(=X)-NH2], an aldehyde (R -CHO) and a )5-ketoester (R -CO-CH2-CO-R ) has provided a wide range of anti-tumour candidates. " Using an ion-tagged iron catalyst - an imidazolium with FeC " or Fe2Cl7 as counterion - the reaction can be carried out under ionic liquid conditions. 

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