Search

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. [ABSTRACT FROM AUTHOR]

In this article, a synthesis of N '-(benzylidene)-2-(6-methyl-1 H -pyrazolo[3,4- b ]quinolin-1-yl)acetohydrazides and their structural interpretation by NMR experiments is described in an attempt to explain the duplication of some peaks in their 1 H- and 13 C-NMR spectra. Twenty new 6-methyl-1 H -pyrazolo[3,4- b ]quinoline substituted N -acylhydrazones 6 ( a - t ) were synthesized from 2-chloro-6-methylquinoline-3-carbaldehyde ( 1 ) in four steps. 2-Chloro-6-methylquinoline-3-carbaldehyde (1) afforded 6-methyl-1 H -pyrazolo[3,4- b ]quinoline ( 2 ), which upon N -alkylation yielded 2-(6-methyl-1 H -pyrazolo[3,4- b ]quinolin-1-yl)acetate ( 3 ). The hydrazinolysis of 3 followed by the condensation of resulting 2-(6-methyl-1 H -pyrazolo[3,4- b ]quinolin-1-yl)acetohydrazide ( 4 ) with aromatic aldehydes gave N -acylhydrazones 6 ( a - t ). Structures of the synthesized compounds were established by readily available techniques such as FT-IR, NMR and mass spectral studies. The stereochemical behavior of 6 ( a - t ) was studied in dimethyl sulfoxide- d 6 solvent by means of 1 H NMR and 13 C NMR techniques at room temperature. NMR spectra revealed the presence of N '-(benzylidene)-2-(6-methyl-1 H -pyrazolo[3,4- b ]quinolin-1-yl)acetohydrazides as a mixture of two conformers, i.e., E (C=N)(N-N)   synperiplanar and E (C=N)(N-N) antiperiplanar at room temperature in DMSO- d 6 . The ratio of both conformers was also calculated and E (C=N) (N-N)   syn-periplanar conformer was established to be in higher percentage in equilibrium with the E (C=N) (N-N) anti-periplanar form.