Organocatalytic Enantioselective Synthesis of Axially Chiral N,N'-Bisindoles
Zhi-Han Chen1, Tian-Zhen Li1,2, Ning-Yi Wang1
1Research Center of Chiral Functional Heterocycles, School of Chemistry and Materials Science, Jiangsu Normal University, Xuzhou, 221116, China.
Abstract:
This study establishes the first organocatalytic enantioselective synthesis of axially chiral N,N'-bisindoles via chiral phosphoric acid-catalyzed formal (3+2) cycloadditions of indole-based enaminones as novel platform molecules with 2,3-diketoesters, where de novo indole-ring formation is involved. Using this new strategy, various axially chiral N,N'-bisindoles were synthesized in good yields and with excellent enantioselectivities (up to 87 % yield and 96 % ee). More importantly, this class of axially chiral N,N'-bisindoles exhibited some degree of cytotoxicity toward cancer cells and was derived into axially chiral phosphine ligands with high catalytic activity. This study provides a new strategy for enantioselective synthesis of axially chiral N,N'-bisindoles using asymmetric organocatalysis and is the first to realize the applications of such scaffolds in medicinal chemistry and asymmetric catalysis.
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