2.1. Synthesis of N-substituted maleimide derivative

N-methylolmaleimide was synthesized according to the method Tawney et al. proposed (Figure 1) [47]. At room temperature 90 mL of 5% sodium hydroxide was added to a suspension of 2.910 g of maleimide in 5.559 g of 37% formaldehyde (final pH » 5). Within 10 min all of maleimide was dissolved and a mildly exothermic reaction occurred. Separation of the product was begun promptly. After leaving for 2.5 h at room temperature, the solution was filtered. One recrystallization from ethyl acetate ended 1.12 g of product and it was dried under vacuum to remove solvent.

Methylolation of maleimide.

Bromine functional maleimide was prepared by esterification of N-methylolmaleimide with a-bromoisobutyrl bromide according to the method of Çakır et al. (Figure 2) [48]. Under nitrogen, 1.24 mL (2.307 g, 10 mmol) a-bromoisobutyrl bromide was added dropwise to a stirring mixture of NMM (1 g, 8 mmol) and triethylamine (1.37 mL, 10 mmol) in 23.3 mL of CHCl3 in an ice bath for 1 h. After complete addition of the acid bromide, the reaction was stirred at room temperature for 3 h. A dark red reaction mixture observed and it was washed with water (3 × 23.3 mL) and then dried over MgSO4. After filtration and evaporation of CHCl3, it was dried under vacuum and recrystallized from ethanol.

Esterification of N-methylolmaleimide with BiBB.