Indoles alkyne-tethered, annulation

We have recently reported an intramolecular variant of this annulation process using an alkyne tethered to an indole (Eq. 81) [117,118]. 

In 2014, Rh(III)-catalyzed intramolecular annulation of alkyne-tethered acetanilides for the synthesis of fused tricyclic indoles 3 via C-H activation was developed by the groups of Liu, Jia, and Li [6a-c]. The reactions have a good substrate scope, utilize molecular oxygen as the cooxidant, and proceed with complete regioselectivity. It is interesting to note that only the sterically hindered ortho-C-H bond of the arene moiety participated in C-C bond formation (Eq. (5.3)). Similarly, the cyclization of anilides with allyl carbonates also proceeded to form 2-substituted indoles 4 (Eq. (5.4)) [6d]. 

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