A useful synthetic route to n-nonsubstituted succinimides via light-induced degradation of metallocarbonyl complexes

Abstract

Succinimides are among the most studied compounds due to their wide profile of biological activities. It is well-known that succinimides undergo ring-opening reactions under alkaline conditions. This feature limits the formation of 3-substituted succinimides from maleimides by an oxa-Michael reaction, for which basic conditions are required. Herein, we report the synthesis, characterization, and crystal structure of metallocarbonyl (Fe, Ru) complexes bearing 3-substituted succinimide ligands. These complexes were obtained in oxa-Michael reactions of CpM(CO)2(η1-maleimidato) (M = Fe, Ru) with alcohols (MeOH, EtOH) in the presence of K2CO3. During the crystallographic studies of an iron complex bearing the 3-methoxysuccinimide ligand, we also identified unexpected crystals of free 3-methoxysuccinimide. We performed some additional experiments and theoretical calculations to determine the mechanism of formation of the obtained N-nonsubstituted succinimide. We demonstrate that 3-methoxysuccinimide resulted from light-induced degradation of CpFe(CO)2(η1-3-methoxysuccinimidato). On the basis of these findings, we propose an indirect route leading to 3-substituted succinimides starting from maleimide via the light-induced degradation of iron metallocarbonyl succinimidato complexes. The proposed methodology prevents ring opening of succinimide under alkaline conditions and gives N-nonsubstituted succinimide products. To confirm the effectiveness of the described method, CpFe(CO)2(η1-maleimidato) was allowed to react with several aliphatic alcohols and phenol, affording the oxa-Michael reaction products in the case of primary alcohols. The irradiation of the obtained compounds with daylight gave the N-nonsubstituted 3-alkoxysuccinimides.