Brønsted Acid–Catalyzed Friedel–Crafts Reaction of Indoles to α-Ketimino Esters

<div><p></p><p>Friedel–Crafts reaction of indoles to aromatic α-ketimino esters was found to be catalyzed by camphorsulfonic acid with good yields (up to 98%) under ambient temperature. This process provides an efficient method for the synthesis of unnatural amino acid derivatives that bear quaternary carbon centers.</p>