Highly Enantioselective Copper- and Iron-Catalyzed Intramolecular Cyclopropanation of Indoles

We report the first intra­molecular
enantio­selective
cyclo­propanation of indoles, which was accomplished in good
to high yield (up to 94%) with excellent enantio­selectivity
(up to >99.9% ee) by using copper or iron complexes of chiral spiro
bis­oxazolines as catalysts. This reaction is a straightforward,
efficient method for constructing polycyclic compounds with an all-carbon
quaternary stereogenic center at the 3-position of the indole skeleton,
a core structure shared by numerous natural products and bioactive
compounds.