Indoles synthesis benzene ring functionalization

After this work, the more challenging synthesis of arene-alkynylated indoles was investigated. Because of the enhanced reactivity of the pyrrole ring, the direct functionalization of indoles on the benzene ring is highly challenging. A domino process to access these compounds would therefore be very useful. They were able... 

In 2005, Ohno et al. reported a cascade intramolecular carbopalladation/aromatic C-H bond activation for the synthesis of tri- or tetracyclic heterocycles 174 in the presence of palladium species [70] (Scheme 6.48). The authors proposed that this domino reaction might proceed through the oxidative addition of bromoenyne 173 to Pd(0), insertion of the alkyne into the C-Pd bond of intermediate 175, followed by C-H bond functionalization of the aromatic ring. Not only benzene-substituted substrates but also heteroaromatic rings such as benzofuran and indole, could be introduced efficiently to this reaction. Similar work was reported by Chernyak and Gevorgyan [71]. 

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