V. Outlaw, C. Townsend
Dec 5, 2014
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Influential Citations
23
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Journal
Organic Letters
Abstract
Among privileged structures, indoles occupy a central place in medicinal chemistry and alkaloid research. Here we report a flexible and efficient conversion of pyrrole-3-carboxaldehydes to substituted 7-amino-5-cyanoindoles. Phosphine addition to fumaronitrile proceeds with prototropic rearrangement of the initially formed zwitterion to the thermodynamically favored phosphonium ylide, which is poised for in situ Wittig olefination. The predominantly E-alkene product positions the allylic nitrile for facile intramolecular Hoeben–Hoesch reaction in the presence of BF3·OEt2. Syntheses of 2,5- and 3,5-disubstituted 7-aminoindoles are illustrated. Additionally, dianion alkylation of the allylic nitrile is demonstrated to furnish, after cyclization, 5,6-disubstituted 7-aminoindoles to further exemplify this scalable and high-yielding method.