PEG 1000-Based Dicationic Acidic Ionic Liquid Catalyzed One-Pot Synthesis of 4-Aryl-3-Methyl-1-Phenyl-1 H-Benzo [ h ] pyrazolo [ 3 , 4-b ] quinoline-5 , 10-Diones via Multicomponent Reactions

A novel and green approach for efficient and rapid synthesis of 4-aryl-3-methyl-1-phenyl-1H-benzo[h]pyrazolo[3,4-b]quinoline-5,10-diones has been accomplished by the one-pot condensation reaction of aromatic aldehydes, 3-methyl-1-phenyl-1H-pyrazol-5-amine and 2-hydroxynaphthalene-1,4-dione using PEG1000-based dicationic acidic ionic liquid (PEG1000-DAIL) as a catalyst was reported. Recycling studies have shown that the PEG1000-DAIL can be readily recovered and reused several times without significant loss of activity. The key advantages are the short reaction time, high yields, simple workup, and recovered catalyst.


Introduction
Green organic chemistry offers enhanced chemical technology procedures economics concomitant with a reduced environmental degradation.From this viewpoint, it is desirable to achieve multi-bond formation in one operation.Multicomponent reactions (MCRs) allow the creation of several bonds in a single operation and are attracting increasing attention as one of the most powerful emerging synthetic tools for the creation of molecular diversity and complexity [1].

Results and Discussion
Initially, the reaction of 3-methyl-1-phenyl-1H-pyrazol-5-amine, benzaldehyde and 2-hydroxynaphthalene-1,4-dione was explored in order to search for the optimal conditions.The results collected in Table 1 clearly suggest that PEG1000-DAIL catalyzed efficient for the three-component reaction, and the yield rose to 89% (Table 1, entries 8 and 9) by increasing the temperature.Increasing the reaction temperature could remarkably enhance both reaction yield and rate, perhaps because ionic liquid and toluene could form a homogeneous phase at high temperature.The results showed that the appreciable temperature was reflux temperature, 110 °C (Table 1, entry 9).The condensation of 3-methyl-1-phenyl-1H-pyrazol-5-amine, benzaldehyde and 2-hydroxynaphthalene-1,4-dione under the conditions described in Table 1 with PEG1000-DAIL as catalysts was run for six consecutive cycles with satisfying results (Table 1, entry 9).The underlayer of PEG1000-DAIL was reused without any treatment and the work-up procedure of recycling is accomplished by simple phase separation only.
Under the optimized reaction conditions, we investigated the reaction of 3-methyl-1-phenyl-1Hpyrazol-5-amine, 2-hydroxynaphthalene-1,4-dione with various aromatic aldehydes (Table 2).Table 2 showed the aromatic aldehydes with electron-donating groups such as methoxy, methyl proceeded at faster rates than those with electron-withdrawing groups such as chloro, nitro.However, the whole reaction proceeded at reflux temperature within 6 h in excellent yields.

General Procedure
The PEG1000-DAIL was prepared by the procedure given in the literature [23].All the other chemicals and reagents are obtained from commercial resource.Commercially available reagents were used without further purification.All products were known compounds and were identified by their Mp, NMR, IR and Anal.Calcd.Melting points were obtained with a Shimadzu DSC-50 thermal analyzer from Shimadzu Corporation, Kyoto, Japan.NMR spectra were recorded with a Bruker Advance instrument from Bruker Corporation, Karlsruhe, Germany.IR (KBr) spectra were recorded on NICOLET Impact410 spectrophotometer from Nicolet Corporation, Denver, USA.Elemental analyses were performed by a Vario-III elemental analyzer from Elementar Corporation, Hanau, Germany.

Conclusions
In conclusion, we have successfully developed an easy and efficient method to prepare a variety of 4-aryl-3-methyl-1-phenyl-1H-benzo[h]pyrazolo [3,4-b]quinoline-5,10-diones from the reaction of different aromatic aldehydes, 3-methyl-1-phenyl-1H-pyrazol-5-amine and 2-hydroxynaphthalene-1,4-dione in the presence of PEG1000-DAIL.The advantages of our protocol include high yields, easy isolation of the compounds, short reaction times, the elimination of the metals, and good thermoregulated biphasic behavior of PEG1000-DAIL.Moreover, the PEG1000-DAIL could be readily recovered and reused for several consecutive cycles, thus making this methodology environmentally more acceptable.

Table 1 .
Optimizing the reaction conditions.
a Isolated yields.