Gold(I)‐Catalyzed Benzylic C(sp <sup>3</sup> )−H Functionalizations: Divergent Synthesis of Indole[ <i>a</i> ]‐ and [ <i>b</i> ]‐Fused Polycycles**
Luca C. Greiner, Norihito Arichi, Shinsuke Inuki, Hiroaki Ohno
Abstract
Abstract Phenyl azides substituted by an (alkylphenyl)ethynyl group facilitate benzylic sp 3 (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 sp 3 (C−H) functionalization leading to an indole‐fused seven‐membered ring is also demonstrated.