Chiral-Phosphoric-Acid-Catalyzed C6-Selective Pictet-Spengler Reactions for Construction of Polycyclic Indoles Containing Spiro Quaternary Stereocenters

Compared with the well-established asymmetric Pictet-Spengler reactions on the pyrrole ring of indoles, the catalytic asymmetric Pictet-Spengler reaction on the benzene ring of indoles has been rarely studied. Herein the C6-selective Pictet-Spengler reactions of indoles have been realized by employing 2-(1H-indol-7-yl)anilines and isatins in the presence of chiral phosphoric acid, affording novel polycyclic indole derivatives bearing Spiro quaternary stereocenters in excellent yields with excellent enantioselectivities. This reaction could be conducted on the gram scale without any loss of activity or enantioselectivity.

Automated summary

In this study, a catalytic asymmetric Pictet-Spengler reaction on the benzene ring of indoles was achieved using chiral phosphoric acid, resulting in the synthesis of polycyclic indole derivatives with Spiro quaternary stereocenters in excellent yields and enantioselectivities. The reaction could be conducted on a gram scale without any loss of activity or enantioselectivity.