Issue 23, 2009

The coumarin→indole transformation—a method for preparing 4-halo-5-hydroxyindoles from coumarins

Abstract

Readily accessible 3-alkoxycarbonyl-6-hydroxy-5-halocoumarins can be converted into 4-halo-5-hydroxyindoles by a sequence whose essential steps are conjugate reduction or conjugate addition, decarboxylation, lactone opening with ammonia, phenolic oxygen protection, Hofmann rearrangement to an N-Boc ethylamine, oxidation to a quinone and deprotection of the nitrogen. The resulting β-aminoethyl quinone cyclizes to a mixture of quinone imine and indole, and the imine tautomerizes to the indole spontaneously or on treatment with rhodium on alumina.

Graphical abstract: The coumarin→indole transformation—a method for preparing 4-halo-5-hydroxyindoles from coumarins

Supplementary files

Article information

Article type
Paper
Submitted
20 Jul 2009
Accepted
19 Aug 2009
First published
30 Sep 2009

Org. Biomol. Chem., 2009,7, 4862-4870

The coumarin→indole transformation—a method for preparing 4-halo-5-hydroxyindoles from coumarins

E. J. L. Stoffman and Derrick. L. J. Clive, Org. Biomol. Chem., 2009, 7, 4862 DOI: 10.1039/B914580J

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