## 3 Results and Discussion  
### Chemistry  
Oxidation of 6,7-dichloro-2-methyl-5,8-quinolinedione **2** with selenium dioxide in the presence of dioxane gave 6,7-dichloro-5,8-diox-5,8-dihydroquinoline-2-carbaldehyde **3** (Scheme 1).  
2-Hydroxy-5,8-quinolinedione **6** and 2-chloro-5,8-quinolinedione **7** were obtained by oxidation of 2-hydroxyqinolin-8-0 **4** or 2-chloroquinolin-8-0 **5**, respectively, in the presence of sodium chlorate and hydrochloric acid at 60 \({}^{\circ}\)C (Scheme 2).  
Chemical structures of derivatives **3**, **6-7** were characterized by the \({}^{1}\)H and \({}^{13}\)C NMR spectroscopic methods. Moreover, for compound **3**, the 2D (HSQC and HMBC) NMR spectra were performed.  
Three signals were observed in the \({}^{1}\)H NMR spectrum of compound **3** (Table 1). The chemical shift of the proton at the formyl group was observed at 10.35 ppm. Signals located at 8.77 and 8.40 ppm were assigned to the protons at the H4 and H3 positions, respectively. The signals at 191.4, 137.5, and 125.2 ppm were assigned to the carbon atoms at the formyl group and at the C4 and C3 positions, respectively (Table 1 and Figure S5).  
The HMBC spectrum shows that the proton at the formyl group correlates with the carbon atoms at the C2 (155.9 ppm), C3 (125.2 ppm), and C4 (137.5 ppm) positions. The spectrum shows also a correlation of proton at the H4 position with the carbon atoms at the C5 (175.0 ppm), C2 (155.9 ppm), and C8A (147.0 ppm) positions. Another correlation was observed between the proton at the H3 position and carbon atoms at the C2 (155.9 ppm) and C4A (130.4 ppm) positions (Table 1 and Figure S6).  
In the HMBC spectrum, a correlation between carbon atoms at the C6, C7, and C8 positions was not observed. For this reason, a simulation of the NMR spectrum was performed using the GIAO method [42; 43]. The experimental and calculated chemical shifts for compound 3 are presented in Table 2.  
According to the calculated spectrum, the signal at 173.7 ppm was assigned to the carbon atom at the C8 position. The chemical shifts of carbon atoms at the C6 and C7 positions were observed at 143.6 and 145.1 ppm, respectively. Figure 2 shows a good agreement between experimental and calculated \({}^{13}\)C and \({}^{1}\)H NMR spectra for compound 3 (R = 0.9756 and R = 0.9991, respectively).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Proton**} & \multicolumn{2}{c}{\({}^{1}\)**H NMR**} & \multirow{2}{*}{**HSQC**} & \multirow{2}{*}{**Carbon**} & \multicolumn{2}{c}{\({}^{13}\)**C NMR**} \\  & **\(\delta\) (ppm)** & & & \(\delta\) (ppm) & **HMBC** \\ \hline CHO & 10.35 & 10.35–191.4 & CHO & 191.4 & 10.35–155.9 (C2) \\  & & & & 10.35–137.5 (C4) & 10.35–125.2 (C3) \\ H4 & 8.77 & 8.77–137.5 & C4 & 137.5 & 8.77–147.0 (C8A) \\  & & & & 8.77–155.9 (C2) \\  & & & & 8.77–175.0 (C5) \\ H3 & 8.40 & 8.40–125.6 & C3 & 125.2 & 8.40–155.8 (C2) \\  & & & & 8.40–191.4 (CHO) \\ \hline \hline \end{tabular}
\end{table}
Table 1: The chemical shifts (\({}^{1}\)H NMR and \({}^{13}\)C NMR spectra) and correlations proton–carbon (HSQC and HMBC experiments) for derivative 3.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Atoms**} & \multicolumn{2}{c}{**Chemical Shift \(\delta\) (ppm)**} \\ \cline{2-3}  & \multicolumn{2}{c}{**Experimental**} & \multicolumn{2}{c}{**Calculated**} \\ \hline CHO & 10.35 & 11.63 \\ H4 & 8.77 & 8.69 \\ H3 & 8.40 & 7.73 \\ CHO & 191.4 & 194.8 \\ C2 & 155.9 & 166.1 \\ C3 & 125.2 & 124.9 \\ C4 & 137.5 & 134.1 \\ C4A & 130.4 & 126.5 \\ C5 & 175.0 & 177.5 \\ C6 & 143.6 & 152.8 \\ C7 & 145.1 & 1