Organocatalytic Asymmetric Annulation between Hydroxymaleimides and Nitrosoarenes: Stereoselective Preparation of Chiral Quaternary N-Hydroxyindolines

An unusual and highly effective asymmetric annulation of nitrosoarenes with hydroxymaleimides catalyzed by a chiral bifunctional amine squaramide catalyst has been disclosed. A wide range of highly fused chiral N-hydroxyindolines with two consecutive quaternary stereocenters and multifunctional groups were directly and effectively prepared in excellent yields (up to >99%) with complete regioselective cyclization and excellent stereoselectivities (up to >99:1 dr and >99% ee). The efficiency and potentials of the new reaction and the target chiral entities were well demonstrated by delicate transformations into a series of new chiral indolines.