Enantioselective Friedel–Crafts Alkylation of Indoles with Alkylidene Malonates Catalyzed by N,N′‐Dioxide–Scandium(III) Complexes: Asymmetric Synthesis of β‐Carbolines

An efficient catalytic asymmetric Friedel-Crafts alkylation of indoles with alkylidene malonates has been developed by using a chiral N,N'-dioxide-Sc(OTf)(3) complex as the catalyst (see scheme). Some optically active intermediates containing the indole skeleton have been synthesized, such as indolepropionic acid, tryptamines, and beta-carbolines. The coordination between the scandium atom and the chiral N,N'-dioxide compound has been revealed by X-ray structure analysis.