<scp>Copper‐Catalyzed</scp> Modular Access to <scp><i>N</i>‐Fused</scp> Polycyclic Indoles and <scp>5‐Aroyl</scp>‐pyrrol‐2‐ones <i>via</i> Intramolecular N—H/C—H Annulation with Alkynes: Scope and Mechanism Probes
Yanhua Liu, Hong Song, Chi Zhang, Yue‐Jin Liu, Bing‐Feng Shi
Abstract
Summary of main observation and conclusion Copper‐catalyzed intramolecular N—H/C—H annulation with alkynes has been developed. A variety of densely functionalized heterocycles, such as pyrrolo[1,2‐ a ]indoles, indolo[1,2‐ c ]quinazolin‐2‐ones, oxazolo[3,4‐ a ]indoles, and imidazo[1,5‐ a ]indoles, were synthesized in an atom‐ and step‐economical manner, owing to the high modularized feature of aniline moiety, the linker moiety, as well as the alkyne moiety. By simply changing the oxidant from di‐ tert ‐butyl peroxide (DTBP) to 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO), the reaction could readily be transformed to the aminooxygenation pathway, which grabs one oxygen atom from the TEMPO to generate 5‐aroyl‐pyrrol‐2‐ones. Mechanistic experiments indicate that vinyl radical is involved in this reaction and an amidyl‐radical‐initiated radical cascade might be responsible for this transformation.