Pd-Catalyzed Enantioselective Construction of Isoindolo[2,1-a]indoles.

Isoindolo[2,1-a]indoles are a class of important functionalized indole-based heterocycles with significant utility in natural products, pharmaceuticals, and functional materials. Larock isoindolo[2,1-a]indole synthesis is one of the most straightforward and efficient methods for the synthesis of isoindolo[2,1-a]indole utilizing internal alkynes and imines derived from o-iodoanilines and aldehydes based on Larock indole synthesis. However, developing an asymmetric version for the construction of chiral isoindolo[2,1-a]indoles has posed considerable challenges since its initial report in 1999. Herein, we report a first example of asymmetric Larock isoindolo[2,1-a]indole synthesis by employing a chiral sulfinamide phosphine (Sadphos) ligand (Ming-Phos) with modification. It allows rapid transformation of a wide range of substrates in good to excellent enantioselectivities, and provides a facile and straightforward access to chiral isoindolo[2,1-a]indole fused heterocycles. Notably, these chiral isoindolo[2,1-a]indole fused heterocycles exhibit bright fluorescence. The optical properties, including circular dichroism and quantum yield, are examined. The transformation offers a chiral highly conjugated system, which could have great potential applications in chiral optoelectronic materials.