Access to Indole‐Fused Benzannulated Medium‐Sized Rings through a Gold(I)‐Catalyzed Cascade Cyclization of Azido‐Alkynes

Abstract

Ag olden compass guides the adventurer's way in an unknown chemical space from the structures with one-and two-dimensional content towards those with an increased three-dimensional character.T hese three-dimensional compounds rise towards uncharted chemical space leaving the flatland behind, based on the cascade cyclization of alkynyl azides generating indole fused medium-sized rings.

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

“…31 This concept was further extended by Gagosz and Zhang to cascade cyclizations, 32,33 in which an umpolung reactivity for indole was established for unusual nucleophilic functionalizations at the C3 position. Based upon this reactivity, multiple polycyclic indole syntheses have been reported by the groups of Zhang, 32 Ye, [34][35][36][37][38] Xu, 39 and Hashmi, 40,41 and by our group [42][43][44][45][46][47][48] (Scheme 1A). 49 Although the involvement of C-H functionalization via a 1,5-hydride shift-based internal redox process has been observed for gold complexes with keteniminium, 50 furyl, 51 allenyl, 52,53 alkynyl, [54][55][56][57] vinyl cation, 58 unfunctionalized carbene, 59 and oxo carbene species, 60 these processes are unprecedented among -imino gold carbenes.…”

“…In our ongoing endeavors in reaction development using gold catalysis, [42][43][44][45][46][47][48]65,66 we previously reported the synthesis of acenaphthenes 2, which can be rationalized by a 1,5-hydride shift on a vinyl cationic gold complex A generated from allenynes 1 (Scheme 1B). 65 From this vantage point, we envisioned that a 1,5-hydride shift leading to electrophilic -imino gold carbene functionalization should also be conceivable in gold-catalyzed electrophilic C-H functionalization, leading to fused indoles such as 4 (Scheme 1C), which often exhibit biologically intriguing properties.…”