Asymmetric Synthesis of 1,1,1-Triarylethanes by Chiral Imidodiphosphoric Acid Catalyzed Nucleophilic Addition of Pyrrole and Indoles to 3‑Vinylindoles

Chiral
imidodiphosphoric acids were employed as efficient catalysts
in the enantioselective addition reaction of pyrrole and indoles to
3-vinylindoles. A series of optically active 1,1,1-triarylethmanes
bearing quaternary stereocenters were synthesized in excellent yields
(up to 99% yield) and enantioselectivities (up to 98% ee). Gram-scale
reactions of 1i and 2a as well as 1o and 5a demonstrated the synthetic utility
of this methodology. Control experiments showed that the formation
of a double H-bond between the catalyst and substrates is necessary
for an excellent outcome.