Photoredox Catalysis: Construction of Polyheterocycles via Alkoxycarbonylation/Addition/Cyclization Sequence

Abstract

A novel visible-light-induced cascade reaction for the preparation of ester-functionalized polyheterocycles was developed under metal-free conditions, which was initiated by an intermolecular radical addition to a carbon-carbon double bond of N-arylacrylamide derivatives using alkyl carbazate as the ester source followed by cyano-mediated cyclization. The desired phenanthridine derivative products were isolated in moderate to high yields with broad substrate scope.

Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

“…Notably, this process was characterized by mild conditions, operational simplicity, excellent functional group tolerance and offered high yields [86]. By following analogous approaches, the addition of perfluoroalkyl [87], acyloxy [88], or alkyl [89,90] Photocatalytically generated amidyl radicals were adopted for a direct oxidative C-H amidation, offering a straightforward access to phenanthridones (Scheme 18). The process took place upon blue LED irradiation (20-24 h at 60 °C were required) of the chosen substrates (e.g., 18.1a-d) in the presence of the Ir-based photoredox catalyst Ir[dF(CF 3 )ppy] 2 (bpy)PF 6 (2.5 mol %) and a phosphate base (50 mol %).…”

Recent Advances in Radical‐Enabled Bicyclization and Annulation/1,n‐Bifunctionalization Reactions

“…Sun and co-workers first prepared theseh ighly reactive N-(2-cyanobiphenyl) acrylamides and developed their radical bicyclization chemistry in combinationw ith alkyl carbazate as the ester source under photocatalytic conditions. [41] The authorsa lso proposed ar eaction mechanism, as shown in Scheme22b.I nitially, under visible light, the excited state of eosin Y* activates TBHP to release a tert-butoxyl radical, togetherw ith eosin Y + + itself. Then, the tert-butoxyl radical captures ah ydrogen atom from methyl carbazate to produce nitrogen radical intermediate 74.N ext, alkoxycarbonylr adical 76 is generated through sequential dehydrogenation, along with the release of nitrogen gas.…”

“…Undoubtedly, N‐( 2‐cyanobiphenyl) acrylamides have great potential for radical bicyclization reactions. Sun and co‐workers first prepared these highly reactive N‐( 2‐cyanobiphenyl) acrylamides and developed their radical bicyclization chemistry in combination with alkyl carbazate as the ester source under photocatalytic conditions . This reaction worked well in the presence of cheap and available eosin Y (2.0 mol %) as a photocatalyst and TBHP (4.0 equiv) under visible‐light irradiation (5 W, white LEDs), thereby providing access to 30 examples of ester‐functionalized pyrido[4,3,2‐ gh ]phenanthridin‐5(6 H )‐ones in 45–81 % yields (Scheme a).…”

Synthesis of Cyclic Compounds via Photoinduced Radical Cyclization Cascade of C=C bonds

“…Using the N‐arylacrylamide derivatives that bearing ortho‐ cyano groups as radical acceptors, the group of Sun has developed a series of diverse radical triggered addition/cyclization cascades for the preparation of various functionalized tatracyclic phenanthridines via photoredox catalysis. For instance, they have recently utilized the methyl carbazate as ester source to synthesize ester‐functionalized pyrido[4,3,2‐ gh ]phenanthridine derivatives (Scheme ) . Under visible‐light irradiation, the methyl carbazate 149 was converted into corresponding alkoxycarbonyl radical 151 by hydrogen abstraction, dehydrogenation and N 2 elimination.…”