Cascade Reactions of Aryl‐Substituted Terminal Alkynes Involving in Situ‐Generated α‐Imino Gold Carbenes

Abstract

An efficient, highly selective and divergent synthetic method to construct 2‐substituted indoles and aryl‐annulated carbazoles via the intermolecular generation of α‐imino gold carbenes from terminal alkynes or diynes in combination with sulfilimines is disclosed. Importantly, the tandem reaction is proposed to proceed through an intermolecular gold carbene generation/ C‐H annulation followed by the activation of a second alkyne leading to 6‐endo‐dig cyclization, which is significantly different from previous dual activation or 1,6‐carbene shift approaches for diyne systems. In the case of ortho‐alkynylaniline as starting material, an unexpected regioselective formation of the indole moiety via the intermolecular path, instead of intramolecular hydroamination was discovered. This reactivity paved the way for a one‐pot synthesis of the 11H‐indolo [3,2‐c] quinoline scaffold by exploiting the formed amino indole for a subsequent Pictet‐Spengler reaction with aldehydes. The photophysical properties of the carbazoles indicated good violet‐blue emission with quantum yields up to 40%.

Construction of 2-Substituted-3-aryl Benzofurans and Indoles through an Acid-Catalyzed Cascade Intramolecular Friedel-Crafts Reaction/Rearrangement/Aromatization Process

“…Current strategies for synthesizing the titled 2-substituted-3-aryl indole and benzofurans typically involve both traditional and modern synthetic methods, each with its advantages and limitations (Scheme a) . For example, traditional approaches like (i) transition-metal-catalyzed or base-promoted arylation, − (ii) alkylation or dimerization, and (iii) transition-metal-catalyzed intermolecular oxidative annulation − often rely on multistep reactions and complex reaction conditions, leading to low overall yields and increased production costs. In contrast, the intramolecular C–N construction techniques, such as (iv) transition-metal-catalyzed cyclization , and (v) intramolecular amination/oxygenation − offer more efficient and sustainable routes to these compounds.…”

Palladium(ii)-catalyzed intramolecular C–H amination to carbazole: the crucial role of cyclic diacyl peroxides

“…Among various synthetic approaches towards carbazole derivatives, 22 transition-metal-catalyzed C–H amination of 2-phenylaniline derivatives represents one of the most rapidly expanding strategies, because of the practical, atom-economical and step-economical conversion of complex precursors to the corresponding carbazoles. In this regard, two representative reaction mechanisms have been developed (Scheme 1C).…”