Visible-Light-Induced Annulation of Iodonium Ylides and 2-Isocyanobiaryls to Access 6-Arylated Phenanthridines

Abstract

A 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4-CzIPN)-photocatalyzed cascade arylation/cyclization reaction of 2-isocyanobiaryls and iodonium ylides was established for the synthesis of 6-arylated phenanthridines. This is the first example of employing iodonium ylides as aryl radical sources in a visible-lightinduced radical cascade cyclization reaction.

Visible-Light-Mediated Annulation/Thiolation of 2-Isocyanobiaryls with Disulfides to Organoylthiophenanthridines Derivatives

“…According to the results above and previous reports, , two plausible mechanisms for the visible-light-mediated cyclization/thiolation were brought forward in Scheme . First, the photocatalyst 4-CzIPN ( PC ) converts to its excited state PC* under the irradiation of a blue LED, which is quenched by diphenyldisulfide 2a to form the phenylthio radical (detected by GC-MS) and then reacts with 2-isocyanobiaryls 1a to give radical A followed by an intramolecular annulation to give radical B .…”

“…Thus, challenges still exist in developing green, mild, and atom-economical methods for the construction of organoylthiophenanthridines. Encouraged by our previous work on the construction of 6-arylatedphenanthridines via the annulation of iodonium ylides with 2-isocyanobiaryls, herein, we report the cascade annulation/thiolation of 2-isocyanobiaryls with dialkyl­(aryl)­disulfides through the visible-light-induced C–S and C–C bond formation under oxidant, base, and transition-metal-free conditions, delivering a series of organoylthiophenanthridines in good to excellent yields with wild functional group tolerance (Scheme c).…”

“…In addition, these peroxide-promoted annulations need to be performed under a nitrogen atmosphere or equivalent strong alkaline. In 2015, Chen’s group found that the tandem reactions of 2-biaryl isothiocyanates and diaryliodonium salts can proceed effectively to give a series of arylthiophenanthridines in moderate to good yields catalyzed by 10 mol % of CuCl (Scheme b) . However, a transition-metal catalyst must be used, and the reaction needs to be carried out at a high temperature of 100 °C.…”

Recent Advancements in Synthesis of Phenanthridines via 2‐Isocyanobiphenyls

“…For the first time in 2023, Wei-Min He and collaborators demonstrated a visible light induced radical cascade cyclization reaction by exploiting iodonium yilides as aryl radical source. [90] This methodology is an efficient synthetic route for the synthesis of 6-arylated phenanthridines 163 by using CzIPN as a photocatalyst. This protocol showed great functional group tolerance and the best results were achieved under the conditions of 2 mol % CzIPN as the photocatalyst, 1 equiv.…”

Visible-Light-Driven α-C(sp3)–H Bond Functionalization of Glycine Derivatives

“…This reaction highlights the introduction of a novel alkylation reagent for the modification of glycine derivatives coupled with the utilization of an organic photocatalyst. The fluorophore 4CzIPN, characterized by its inherent stability and conducive photoredox potential, has emerged as a compelling organic photocatalyst in recent investigations [114][115][116][117]. Within this context, Cai and colleagues documented a 4CzIPN-catalyzed visible-light-induced α-C(sp 3 )-H alkylation of glycine derivatives using N-alkoxyphthalimides as the radical precursors (Scheme 23) [118].…”