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