Hydroxy-Directed Enantioselective Hydroxyalkylation in the Carbocyclic Ring of Indoles

A Cinchona-derived squaramide catalyzes the reaction
between hydroxyindoles and isatins leading to enantioenriched indoles
substituted in the carbocyclic ring. The reaction proceeds efficiently
with differently substituted isatins, yielding the desired products
with excellent regioselectivity, good yields, and high enantiocontrol.
Moreover, every position of the carbocyclic ring of the indole can
be functionalized by using the appropriate starting hydroxyindole.
The OH group was removed smoothly upon hydrogenolysis of the corresponding
triflate.