Because the indole ring is a ubiquitous heterocycle in natural products, the development of methods for constructing chiral polycyclic systems with indole skeletons would facilitate the efficient synthesis of indole-containing natural products and pharmaceuticals and thus has recently drawn considerable attention. Transition-metal-catalyzed asymmetric intramolecular cyclopropanation of olefins is a powerful tool for constructing fused ring systems from simple linear substrates, and non-enantioselective intramolecular cyclopropanation of indoles has been used for the synthesis of indole-containing polycyclic compounds and indole alkaloids, such as communesin F, minfiensine, aspidofractinine, and lundurines. However, enantioselective versions of this reaction remain unexplored.

We herein 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 chiral center at the 3-position of the indole skeleton, a core structure shared by numerous natural products and bioactive compounds. Moreover, the donor–acceptor-type cyclopropane moiety of the cyclopropanation product enabled numerous additional transformations, allowing us to synthesize several complex polycyclic products with high stereospecificity.
 

Read more:
Huan Xu, Yi-Pan Li, Yan Cai, Guo-Peng Wang, Shou-Fei Zhu*, Qi-Lin Zhou*. Highly enantioselective copper- and iron-catalyzed intramolecular cyclopropanation of indoles. J. Am. Chem. Soc. 2017, 139, 7697‒7700.

http://pubs.acs.org/doi/abs/10.1021/jacs.7b03086