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Synthesis

Indolines made easy

Route offers quick access to a scaffold frequently found in bioactive molecules

by Bethany Halford
July 26, 2019 | A version of this story appeared in Volume 97, Issue 30

 

Reaction scheme showing N-aryl-N-hydroxy carbamates cyclizing to form an indoline.

Chemists don’t have great options if they want to make molecules containing indoline—a scaffold featuring a benzene ring fused to a nitrogen-containing five-membered ring. Indolines appear in many bioactive molecules. But the reactions used to construct this motif require starting materials that are difficult to make or that produce only simple indolines. Now, the University of Delaware’s Donald A. Watson, Feiyang Xu, and Katerina M. Korch have developed a way to synthesize structurally complex indolines from easily accessible N-aryl-N-hydroxy carbamates (Angew. Chem., Int. Ed. 2019, 10.1002/anie.201907758). The transformation is a modified Heck reaction that uses a palladium catalyst to connect two components in the same molecule­—an alkene and an N-aryl-N-hydroxy carbamate (example shown). In a single step, the cyclization reaction creates complex indolines that are difficult to make otherwise, and the N-aryl-N-hydroxy carbamate starting materials are easy to make from nitroarenes. In addition to its utility for making indolines, Watson notes, the reaction represents an advance in Heck-like reactions of nitrogen electrophiles.

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