The role of a Lewis acid in the Nenitzescu indole synthesis

A highly efficient Lewis acid-catalyzed method for the Nenitzescu synthesis of 5-hydroxyindoles with a range of substituents at N-1 and C-3 and symmetric 5,5′-dihydroxydiindoles has been developed. The amount of the catalyst (10–100 mol %) required depended on the nature of the enaminone component. It has been shown that Lewis acid plays a role in enaminone component activation through an enamine-ZnC12 complex followed by its deprotonation.

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