Highly modulated bisindoles: ligands for copper‐catalyzed Sonogashira reaction
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Abstract
Bisindoles (BIMs) were modulated as powerful N,N′ donor ligands for the copper‐catalyzed Sonogashira reaction. Ligand screening experiments on 11 BIM compounds found that 3,3′‐(4‐chlorophenyl)methylenebis(1‐methyl‐1 H ‐indole) (10%) efficiently accelerated CuCl (5%)‐catalyzed cross‐coupling of aryl iodides with terminal alkynes. A wide range of substituted aryl iodides and/or alkyl‐ and aryl‐substituted terminal alkynes were examined, leading to the corresponding coupling products with yields up to 99%. An efficient and scalable protocol for the synthesis of BIM ligands on a gram scale, with extremely low catalyst loading of o ‐ClC 6 H 4 NH 3 + Cl − , was also developed with a reaction time of 20 min with yields up to 93%. This novel N,N′ ligand was air‐stable, easily available and highly modulated with low copper loading. Copyright © 2016 John Wiley & Sons, Ltd.