Catalytic Asymmetric Four-Component Reaction for the Rapid Construction of 3,3-Disubstituted 3‑Indol-3′-yloxindoles

A Rh­(II)/chiral phosphoric acid cocatalyzed
four-component reaction
of indoles, 3-diazooxindoles, arylamines, and ethyl glyoxylate is
developed, offering an extremely efficient strategy for the construction
of 3,3-disubstituted 3-indol-3′-yloxindoles with excellent
diastereoselectivities and high to excellent enantioselectivities.
This transformation is proposed to proceed through a Mannich-type
trapping of the zwitterionic intermediate generated from a metal carbene
and an indole with an iminoester derived from an arylamine and a glyoxylate.