Organocatalytic Asymmetric [3 + 2] Cyclization: Enantioselective Synthesis of α-Indolyl Pyrrolo[1,2-a]indole Scaffolds

A novel asymmetric [3 + 2] cyclization of α-indolyl propargylic alcohols with 3-alkyl-1H-indoles via chiral phosphoric acid catalysis has been established. This strategy allowed the synthesis of chiral α-indolyl pyrrolo[1,2-a]indole derivatives with high yields (up to 91%) and excellent enantioselectivities (up to 99% ee), facilitating both the reaction activity and enantioselectivity by using the solvent of CH₃CFCl₂. Significantly, this protocol will provide an effective synthetic approach for constructing enantioenriched α-indolyl pyrrolo[1,2-a]indole cores of antimalarial natural product isoborreverine analogues.