Transition-metal-free oxindole synthesis: quinone–K₂CO₃ catalyzed intramolecular radical cyclization

Abstract

A novel and highly efficient transition-metal-free approach for the conversion of α-bromoanilides to 3,3-disubstituted oxindoles is described. This transformation is promoted by catalytic amount of 9,10-phenanthrenequinone (PQ) together with K2CO3,...

Electron‐Deficient Phenanthrenequinone Derivative for Photoactivated Hydrogen Atom Transfer Mediated Oxidation of Secondary Alcohols

“…We noticed that older batches of PQ resulted in lower yields of 4'‐methoxyacetophenone 5 a , significantly affecting the reproducibility of the benzylic oxidation. In the recent literature, the source of PQ has been reported to have an effect on its reactivity [46] . Initially, we reasoned that this could be caused by the varying purity level, but both recrystallization and sublimation of commercial PQ only decreased its activity.…”

“…In the recent literature, the source of PQ has been reported to have an effect on its reactivity. [46] Initially, we reasoned that this could be caused by the varying purity level, but both recrystallization and sublimation of commercial PQ only decreased its activity. Therefore, we propose that due to its planar structure, as its degree of crystallinity increases, PQ tends to form aggregates exhibiting a lower catalytic efficacy.…”

Construction of N-Polyheterocycles by N-Heterocyclic Carbene Catalysis via a Regioselective Intramolecular Radical Addition/Cyclization Cascade

“…In this background, our group recently developed a novel pathway to 3,3-disubstituted oxindoles (Scheme a), in which the NHC catalyst functions as a reductant for the SET process, which is different from the above-mentioned radical coupling reactions based on Breslow intermediates . As part of our continuous interest in developing redox-neutral radical coupling reactions, , herein we present a sustainable and scalable NHC-catalyzed regioselective intramolecular alkyl radical addition to the nitrile-group-initiated cascade cyclization, which affords various types of pyrido­[4,3,2- gh ]­phenanthridines under mild conditions (Scheme b).…”

Redox-Neutral Generation of Iminyl Radicals by N-Heterocyclic Carbene Catalysis: Rapid Access to Phenanthridines from Vinyl Azides

“…Moreover, we further uncovered a trail of NHC-catalyzed radical coupling reactions , (Scheme a–c) in which the NHC catalyst directly served as a SET reductant for various α-halides, unlike previous reports stemming from Breslow intermediates. As part of our continuous research interest in the construction of diverse heterocycles, , herein we demonstrate a sustainable and redox-neutral route to phenanthridines through NHC-catalyzed intermolecular alkyl radical addition to vinyl azide. The reaction is initiated by a homolytic aromatic substitution (HAS) process in the absence of any external hypervalent iodine reagents or transition-metal catalysts (Scheme d).…”