Gold(I)-Catalyzed Benzylic C(sp3)-H Functionalizations: Product Bifurcation towards Indole[a]- and [b]-Fused Polycycles

Phenylazides substituted by an (alkylphenyl)ethynyl group facilitate divergent benzylic sp3(C-H) functionalization in the presence of a JohnPhosAu catalyst, via N- or C-cyclization, resulting in indole-fused tetra- and pentacycles. The chemoselectivity is influenced depending on the counter-anion (SbF6 or BARF), the electron density of the alpha-imino gold(I) carbene, and the alkyl groups stabilizing the benzylic carbocation originating from a 1,5-hydride shift. An isotop-ic labeling experiment demonstrates the involvement of an indolylgold(I) species resulting in a tautomerization that is much faster than deauration is. The formation of a benzylic sp3(C-H) functionalization resulting in an indole-fused sev-en-membered ring is also demonstrated.