Synthesis, spectroscopy and computational studies of some novel π-conjugated vinyl N-alkylated quinolinium salts and their precursor's

• New synthetic methodologies of π-conjugated vinyl N-methylated quinolinium salts.
• We report new spiro type compounds based on quinoline moieties.
• The X-ray structures of N-alkylated quinolinium salts.
• Multinuclear NMR, IR, UV–Vis, X-ray and DFT characterizations.

A series of π-conjugated vinyl N-methylated quinolinium salts (3) and their precursor's N-alkylated quinolinium salts (2) were prepared and characterized by NMR, IR, UV–Vis and MS spectroscopy. It was confirmed that the hydroxyl and amino derivatives of vinyl N-methylated quinolinium salts lead to spiro type compounds (4). The syntheses of N-alkylated quinolinium salts were successful, and even multigram scale was achievable. The structures of 1,2–dimethylquinolinium iodide (2a) and 1-ethyl-2-methylquinolinium iodide (2b) were determined by single crystal X-ray diffraction method. NMR spectra showed readily diagnostic H-1 and C-13 signals from methyl and N-alkyl groups for both 2 and 3. The geometries of the studied compounds were optimized in singlet states using the density functional theory (DFT) method with B3LYP functional. In general, the predicted bond lengths and angles are in a good agreement with the values based on the X-ray crystal structure data.

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