Organocatalytic Enantioselective Mannich Reaction of Cyclic N -Sulfonyl Ketimines to Tryptanthrin-Derived Ketimines

An organocatalytic asymmetric addition of cyclic N-sulfonyl ketimines to tryptanthrin-derived ketimines has been developed with moderate-to-excellent yields and excellent enantioselectivities (up to 99% yield, 90–99% ee), with a chiral bifunctional tertiary amine–squaramide as the catalyst. This protocol provides an effective method to construct enantiomerically pure 6,6-disubstituted indolo[2,1-b]quinazolinone derivatives containing a cyclic N-sulfonyl ketimine scaffold.