Abstract
Cinnoline 1-oxide (II), cinnoline 2-oxide (III), 4-methylcinnoline 1-oxide (V), 4-methylcinnoline 2-oxide (VI), 3-chlorocinnoline 1-oxide (VIII), and 3-methoxycinnoline 1-oxide (XXI) were synthesized. For confirmation of the structure of these compounds, cinnoline 1-oxide (II) and 3-chlorocinnoline 1-oxide (VIII) were prepared from their corresponding 5, 6, 7, 8-tetrahydro derivatives (XI and XIII) by bromination with N-bromosuccimide followed by dehydrobromination with sodium methoxide. The structures of isomeric 4-methylcinnoline N-oxides were determined by the application of ultraviolet and nuclear magnetic resonance spectroscopies. The nuclear magnetic resonance spectra of the cinnoline N-oxides synthesized were examined. The interpretation of the spectra was made in connection with those of pyridazine N-oxides and of quinoline N-oxides. The proton H8 shows its signal peak at a lower field than do the other protons, owing to the magnetic anisotropy effect of the N-O group.
