## 2 Results
In contrast, the Dynamic method (100 W, 70 \({}^{\circ}\)C) was better due to more precise control of the temperature during the reaction and constant supply of the appropriate amount of microwave radiation. All reactions using a microwave reactor \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Entry** & **n (a)** & **R** & **Product** & **Yield (\%)** \\ \hline
1 & 1 & 4-(Bromomethyl)phenyl & **3a** & 78 \\
2 & 1 & Bromomethyl & **3b** & 46 \\
3 & 2 & 2-Bromomethyl & **3c** & 65 \\
4 & 3 & 3-Bromopropyl & **3d** & 69 \\
5 & 4 & 4-Bromobutyl & **3e** & 71 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Unsymmetrical \(N\),\(N^{\prime}\)-diacylhydrazine derivatives (**3a–e**) derived from benzhydrazide and acid chlorides. were carried out with a reflux reaction device. Studies have shown that the use of MW heating contributes to a significant reduction in the reaction time (1-2.5 h), while the yields of products remain in fact at the same level in comparison to traditional methods. The best yield was achieved in the case of 2-[(4-bromomethyl)phenyl]-5-phenyl-1,3,4-oxadiazol (**4a**), in which three aromatic rings are directly conjugated (93%, Table 2, Entry 6). The yields of the less conjugated 2-bromoalkyl-5-phenyl-1,3,4-oxadiazoles were at the moderate level of 38-75% (Table 2, Entries 7-10). The resulting final products **4a-e** were purified by column chromatography using 2:1 hexane:ethyl acetate by volume as the mobile phase. The next stage comprised the substitution of the bromine-containing 1,3,4-oxadiazoles (**4a-e**) in order to introduce the bis(carboxymethyl)amino group. The typical methodology for introducing such a group into the leading organic unit involves heating alkyl or arylalkyl halides with iminodiacetic acid in a methanol solution of potassium hydroxide [36]. Thus, we decided to check if such a procedure could be applied for the direct substitution of a model derivative of 2-[(4-bromomethyl)phenyl]-5-phenyl-1,3,4-oxadiazol (**4a**). Unfortunately, the reaction did not proceed even with the use of microwave irradiation. In our previous research on the synthesis of symmetrical 1,3,4-oxadiazol derivatives with carboxymethylamino groups, we used diisopropyl ester of iminodiacetic acid (**6**), which showed high reactivity towards oxadiazole derivatives [34]. The synthesis of such a reagent was carried out using iminodiacetic acid and isopropanol in the presence of an acidic catalyst such as concentrated sulfuric acid (Scheme 3). Having ester **6** in hand, we were able to study the substitution reaction in a series of bromine-containing 1,3,4-oxadiazoles (**4a-e**) (Scheme 4). In order to determine the optimal conditions, the reaction between 2-[(4-bromomethyl)phenyl]-5-phenyl-1,3,4-oxadiazole (**4a**) and diethyl iminodiacetate (**6**) was first examined (Table 3). The following agents influencing the reaction yield were tested: bases including triethylamine TEA and sodium carbonate Na\({}_{2}\)CO\({}_{3}\), solvents (acetonitrile, DMF), temperature, and type of heating (traditional, MW). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Entry** & **Conditions** & **n** [**\({}^{\text{(d)}}\)**] & **R** & **Product** & **Time (h)** & **Yield (\%)** \\ \hline
1 & \(\Delta\)t (a) & 1 & 4-(Bromomethyl)phenyl & **4a** & 3 & 90 \\
2 & \(\Delta\)t & 1 & Bromomethyl & **4b** & 8 & 60 \\
3 & \(\Delta\)t & 2 & 2-Bromoethyl & **4c** & 4 & 32 \\
4 & \(\Delta\)t & 3 & 3-Bromopropyl & **4d** & 6 & 73 \\
5 & \(\Delta\)t & 4 & 4-Bromobutyl & **4e** & 6 & 62 \\
6 & MW (b) & 1 & 4-(Bromomethyl)phenyl & **4a** & 1 & 93 \\
7 & MW & 1 & Bromomethyl & **4b** & 2.5 & 65 \\
8 & MW & 2 & 2-Bromoethyl & **4c** & 2 & 38 \\
9 & MW & 3 & 3-Bromopropyl & **4d** & 1.5 & 75 \\
10 & MW & 4 & 4-Bromobutyl & **4e** & 1.5 & 64 \\ \hline \hline \end{tabular} \({}^{\text{(a)}}\) Conventional heating: \(\Delta\)t, oil bath, 70 \({}^{\text{(c)}}\); \({}^{\text{(b)}}\) MW heating: 100 W, 70 \({}^{\text{(c)}}\); \({}^{\text{(c)}}\) number of -CH\({}_{2}\)- groups.  
\end{table}