Catalytic asymmetric construction of 3,3'-spirooxindoles fused with seven-membered rings by enantioselective tandem reactions.

The first catalytic asymmetric construction of a spirooxindole scaffold incorporated with a seven-membered benzodiazepine moiety has been established by a three-component (isatin, 1,2-phenylenediamine, cyclohexane-1,3-dione) tandem reaction catalyzed by a chiral phosphoric acid. Structurally complex spirobenzodiazepine oxindoles with one quaternary stereogenic center are obtained in high yield with excellent enantioselectivity (up to 99% yield, enantiomeric ratio>99.5:0.5). This approach takes advantage of organocatalytic asymmetric tandem reactions to efficiently construct the structurally rigid spirobenzodiazepine oxindole architecture with high enantiopurity in a single transformation, which involves a cascade enamine-imine formation/intramolecular Mannich reaction sequence.