## 3 Results and Discussion  
### Chemistry  
For the preparation of benzo[g]pyrimido[4,5-b]quinolines, three-component reactions assisted by MW irradiation were carried out using as reagents 6-amino-2-(methylthio)pyri,idin-4(3H)-one 1, naphthalene-1,2,4(3H)-trione 2 and benzaldehyde 3a, in equimolar amounts. Taking as a model reaction the synthesis of 4a, we have tested several reaction conditions, combining diverse solvents (ethanol, acetic acid and ethylenglycol), temperatures and power of the microwave source in order to find the optimal conditions (Table 1). It was found that the product 4a is formed with higher yield under solvent/catalyst-free conditions, (Table 1, entry 2). The synthesis of 4a was carried out at reflux (using ethanol, acetic acid, ethylenglycol or a mixture of both) obtaining low yields and longer reaction times in contrast to MW method. When ethanol was used as the solvent by conventional heating, the desired product 4a was obtained after 2 h in low yield (30%, Table 1, entry 7). In the case of using AcOH or AcOH/Ethylenglycol mixtures moderate similar yields were obtained (45-50%, entry 8-10). The extension of reaction times, keeping the same reaction conditions, did not lead to the formation of aromatized derivative. On the contrary, a decrease was observed in the reaction yield and double recrystallization of the crude reaction is required, first using a N,N-Dimethylformamide (DMF)-Ethanol mixture (ratio 1-9 \(v/v\)) and the isolated solid is then recrystallized from ethanol. Considering the optimal conditions, that is, solvent/catalysis-free conditions, and in order to show the generality and scope of this protocol, we tried various aromatic aldehydes, 6-amino-2-(methylthio)pyrimidin-4(3H)-one and 6-amino-3-methyl-2-(methylthio)pyrimidin-4(3H)-one, to prepare a series of compounds **4a-q** (Scheme 2). In all cases, the starting materials were completely consumed, in times ranged between 5 to 9 min, to afford the 5-aryl-2-methyllio-5,12-dihydrobenzo[\(g\)]pyrimido[4,5-]quinoline-4,6,11(3\(H\))-trione derivatives **4a-q** with high yields (70-81%) after easy work-up (Table 2). This reaction permits the use of aromatic aldehydes with electron withdrawing group (EWG) or electron releasing group (ERG), but also to 2- or/and 3-substitutedpyrimidin-4-ones with good \begin{table}
\begin{tabular}{c c c c c} \hline
**Entry** & **Reaction Conditions** & **Time (min)** & **Yield \({}^{**}\) (\%)** \\ \hline
1 & MW (microwave, 150 \({}^{\circ}\)C) solvent/catalysis-free & 10 & 50 \\
2 & MW (200 \({}^{\circ}\)C) solvent/catalysis-free & 5 & 80 \\
3 & MW (150 \({}^{\circ}\)C) AcOH/Ethanol (3:1) & 10 & 50 \\
4 & MW (200 \({}^{\circ}\)C) AcOH/Ethanol (3:1) & 5 & 65 \\
5 & MW (150 \({}^{\circ}\)C) AcOH/Ethylenglycol (3:1) & 10 & 50 \\
6 & MW (200 \({}^{\circ}\)C) AcOH/Ethylenglycol (3:1) & 5 & 70 \\
7 & Reflux, Ethanol & 120 & 30 \\
8 & Reflux, AcOH & 90 & 50 \\
9 & Reflux, AcOH/Ethylenglycol (3:1) & 60 & 45 \\
10 & Reflux, AcOH/Ethylenglycol (1:3) & 60 & 45 \\ \hline \end{tabular} \({}^{*}\) Equimolar amounts of reactants (1.0 mmol). Ratio (\(\
icefrac{\pi}{v}\)) for the solvent mixture; \({}^{**}\) Isolated yield.  
\end{table} 
Table 1: Evaluation of the parameters of the multicomponent reaction (MCR) of compound **4a. \({}^{*}\)**