Synthesis of Novel -Acylhydrazones and Their C-N/N-N Bond Conformational Characterization by NMR Spectroscopy.

In this article, a synthesis of '-(benzylidene)-2-(6-methyl-1-pyrazolo[3,4-]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 H- and C-NMR spectra. Twenty new 6-methyl-1-pyrazolo[3,4-]quinoline substituted -acylhydrazones (-) were synthesized from 2-chloro-6-methylquinoline-3-carbaldehyde () in four steps. 2-Chloro-6-methylquinoline-3-carbaldehyde (1) afforded 6-methyl-1-pyrazolo[3,4-]quinoline (), which upon -alkylation yielded 2-(6-methyl-1-pyrazolo[3,4-]quinolin-1-yl)acetate (). The hydrazinolysis of 3 followed by the condensation of resulting 2-(6-methyl-1-pyrazolo[3,4-]quinolin-1-yl)acetohydrazide () with aromatic aldehydes gave -acylhydrazones (-). Structures of the synthesized compounds were established by readily available techniques such as FT-IR, NMR and mass spectral studies. The stereochemical behavior of (-) was studied in dimethyl sulfoxide- solvent by means of H NMR and C NMR techniques at room temperature. NMR spectra revealed the presence of '-(benzylidene)-2-(6-methyl-1-pyrazolo[3,4-]quinolin-1-yl)acetohydrazides as a mixture of two conformers, i.e.,   and at room temperature in DMSO-. The ratio of both conformers was also calculated and   conformer was established to be in higher percentage in equilibrium with the form.