Diastereo- and enantioselective construction of a bispirooxindole scaffold containing a tetrahydro-β-carboline moiety through an organocatalytic asymmetric cascade reaction.

The first catalytic asymmetric construction of a new class of bispirooxindole scaffold-containing tetrahydro-β-carboline moiety has been established through chiral phosphoric acid-catalyzed three-component cascade Michael/Pictet-Spengler reactions of isatin-derived 3-indolylmethanols, isatins, and amino-ester, which afforded structurally complex and diverse bispirooxindoles with one quaternary and one tetrasubstituted stereogenic centers in excellent stereoselectivities (all >95:5 diastereomeric ratio (d.r.), up to 98:2 enantiomeric ratio (e.r.)). This intriguing class of chiral bispirooxindoles integrated the two important structures of tetrahydro-β-carboline and bispirooxindole, both of them possessing significant bioactivities. This approach also combined the merits of asymmetric organocatalysis and multicomponent tandem reaction, which provided a unique strategy for the preparation of structurally rigid bispiro-architectures with concomitant creation of multiple quaternary stereogenic centers.