Asymmetric 1,4-Reduction of Pyrano[2,3- b ]indoles with Hantzsch Ester by Chiral Phosphoric Acid.

A highly regioselective and enantioselective transfer hydrogenation of pyrano[2,3- b ]indoles with Hantzsch ester has been successfully realized using spiro-chiral phosphoric acid, affording a series of optically active 1,4-reductive adducts, 4,9-dihydropyrano[2,3- b ]indoles, in 34-99% yields with 61-99% ee .