Gold(I)‐Catalyzed Benzylic C(sp3)−H Functionalizations: Divergent Synthesis of Indole[a]‐ and [b]‐Fused Polycycles

Phenyl azides substituted by an (alkylphenyl)ethynyl group facilitate benzylic sp3(C−H) functionalization in the presence of a JohnPhosAu catalyst, resulting in indole‐fused tetra‐ and pentacycles via divergent N‐ or C‐cyclization. The chemoselectivity is influenced depending on the counter‐anion, the electron density of the α‐imino gold(I) carbene, and the alkyl groups stabilizing the benzylic carbocation originating from a 1,5‐hydride shift. An isotopic labeling experiment demonstrates the involvement of an indolylgold(I) species resulting from a tautomerization that is much faster than the deauration. The formation of a benzylic sp3(C−H) functionalization leading to an indole‐fused seven‐membered ring is also demonstrated. The exposure of (alkylphenyl)ethynyl substituted phenyl azides to JohnPhosAu(I) catalysts leads to the divergent synthesis of indole‐fused polycycles via N‐ or C‐cyclization facilitated via benzyl to α‐imino gold(I) carbene 1,5‐hydride shift. The chemoselectivity depends on the counter‐anion, the reactivity of the carbene, and the attached alkyl groups at the benzylic position.