A simple and highly effective water-compatible organocatalytic system for asymmetric direct Michael reactions of linear aldehydes to maleimides

Diarylprolinol silyl ether-based organocatalyst 2, in conjunction with ionic liquid supported (ILS) sulfonic acid 6a as co-catalyst, leads to a novel organocatalyst in aqueous media. The in situ generated catalyst demonstrated high reactivity and stereoselectivity for the Michael reactions of linear aldehydes to maleimides in brine without any organic solvents. For these reactions, up to 76% yield, 9 : 1 dr and 96% ee were obtained for a broad variety of aldehydes and maleimides.