Palladium-Catalyzed Indole Ring Synthesis Yamanaka-Sakamoto-Sonogashira

Palladium-Catalyzed Indole Ring Synthesis Yamanaka-Sakamoto-Sonogashira 

Varelas discovered a novel synthesis of a pyrrolo-p-carboline via a Sonogashira couphng followed by an intramolecular [2+2+2] cychzation (equation 3) [18]. 

Newer conditions to constract indoles from the Sonogashira 2-alkynylanilines are an electrochanical cyclization that avoids the use of metal catalysts aud add or base [31] and the employment of a recyclable sihca-snpported palladinm catalyst [32]. In both cases the yields of indoles are exceUent. Sanz reported a clever synthesis of 4-haloindoles, which can be further functionalized, from 2,3-dihalophenols via a Smiles rearrangement and 

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. 

Sonogashira coupling/cyclization [33], Manabe and indolization to give an assortment of 2,4-disubstituted 

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