Kihara indole synthesis

The ease of acid-catalyzed indoline dehydration presumably reflects the relative stability of the corresponding benzylic carbocation under the silica gel workup conditions. All of the indolines could be dehydrated to indoles with 5% hydrochloric acid. 

Although limited in scope at the present time, the Kihara indole synthesis seems particularly well suited for the synthesis of 3-aryhndoles. 

Indole Ring Synthesis From Natural Products to Drug Discovery, First Edition. Gordon W. Gribble. 2016 John Wiley Sons, Ltd. PubUshed 2016 by John Wiley Sons, Ltd. 

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The little-used Kihara indole synthesis is an example of an intramolecular Barbier reaction applied to the synthesis of 3-phenyl- and 3-aIkyl-3-hydroxyindolines, which can be dehydrated to the corresponding indoles (Scheme 1) [1], In some cases, the dehydration of indoline to indole was spontaneous. The major byproduct in the Kihara indole synthesis is deiodination of the starting ortho-io6o aniline. Some examples are shown in Scheme 1 (equations 2-5). 

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