Wittig-Madelung indole synthesis

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

3-diacylindoles (equation 5) [14], Acid chlorides also function well in this process. 

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Kraus and his group extended their Wittig-Madelung indole synthesis to other activated benzylic systems as shown in Scheme 6 (equations 1-3) [17]. These include phenylsulfonyl, thiomethyl, and cyano, and this team applied this chemistry to a synthesis of the alkaloid isocryp-tolepine. As we saw twice in the previous chapter, the cycli-zation of phosphonium salt 15 affords quinolone 16, which was used to synthesize both neocryptolepine (17) and isocryptolepine (18). 

Scheme 2 Applications of the Wittig-Madelung Indole Synthesis...

Hughes developed a polymer-bound phosphonium salt support for a solid phase Wittig-Madelung indole synthesis (Scheme 8) [21]. The method uses a commercially available polymer-bound triphenylphosphine 22. 

The ring closure (83 — 84) involves an intramolecular Wittig reaction (81CC14). Another variation on the Madelung indole synthesis is provided by the cyclization of o-isocyanobenzenes (85 — 86) (77JA3532). 

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