Titanium-Catalyzed Asymmetric Friedel-Crafts Alkylations
H.-M. Dong, H.-H. Lu, L.-Q. Lu, C.-B. Chen, W.-J. Xiao*
Central China Normal University, Hubei, P. R. of China
07. November 2007 (online)
In an approach complementary to previously reported methods, the authors report an asymmetric Friedel-Crafts alkylation of indoles with ethyl glyoxylates using chiral Ti-BINOL complexes. N-Protected indoles provide higher yields and greater enantioselectivities compared to free indoles, and various substitution patterns on the benzenoid ring of the indole can be tolerated. Three other glyoxylate derivatives were shown to participate, although they lead to lower ee values or bisindole formation.