Science of Synthesis

Joule, J. A., Science of Synthesis Knowledge Updates, (2010) 2, 85.

1-Anilino-1H-indol-5-ols ‌323‌ [from which the N-substituent can be removed (to give ‌324‌) by catalytic hydrogenolysis] can be synthesized from 3-hydroxystyrenes ‌320‌ in a sequence which involves N—C2 bond formation (‌Scheme 112‌).[‌307‌,‌308‌] Following coupling para to the hydroxy and ortho to the alkenyl substituent to give ‌321‌, proton-catalyzed intramolecular interaction (arrows on ‌321‌) between the double bond and the azo group leads to formation of the five-membered ring in ‌322‌, loss of a proton then giving ‌323‌.

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