Improvement of bifunctional organocatalysts performance by water as an additive in the Michael addition of carbonyl compounds to maleimides

The diastereoselective Michael addition of ketones to maleimides using bifunctional organocatalysts presents a significat challenge. We developed a protocol in which the addition of 5 equivalents of water boosted the diastereoselectivity of six-membered ring ketones. However, the results were influenced by steric effects and varied outcomes were observed with different ring sizes of ketones and acyclic carbonyl compounds. The improvement in the asymmetric synthesis of succinimides due to water appears to be more related to hydrogen bonds at the interface rather than a water molecule embedded in the transition state. Additionally, we explored 3-substituted maleimides and found that only those with phenyl and phenylethynyl groups underwent the reaction. Finally, the desymmetrization of N-(2-tert-butylphenyl)maleimide generated the atropoisomer with good selectivity.