On the nucleophilic accession of 1H-benzotriazole to maleimides

According to the quantum chemical calculations of N-phenylmaleimide (PMI) using the LCAO MO method in Huckel p-electron approximation, a maximum deficit of p-electrons is observed on carbonyl carbon atoms; subsequently, a nucleophilic attack of "pyridinic" nitrogen atoms on carbonyl carbon is likely to occur. Moreover, an alternative attack on olefinic atoms with the opening of a multiple bond is possible. Since the nitrogen atoms N1 and N3 are equivalent in nucleophilic reactions of 1H-benzotriazole (BT) and taking the spectroscopic data on the BT adduct into account, it is impossible to conclude that all three nitrogen atoms are involved. For these purposes, it is advisable to use benzotriazoles with substitution in position 5 (or 6), where the nitrogen atoms N1 and N3 are not equivalent in these reactions. The reaction products were analysed using the C-13 NMR-spectroscopy method. The obtained data testify to the preferential occurrence of the nucleophilic attack of benzotriazoles on the multiple maleimide bond during their interaction in the melt at elevated temperatures, as well as on the participation of all three nitrogen atoms of the 1H-benzotriazolyl fragment in the nucleophilic attachment of benzotriazoles to the multiple PMI bond.