Tin-free radical cyclization reactions initiated by visible light photoredox catalysis

Abstract

Herein, we report an advancement in the application of visible light photoredox catalysts in a classic free radical mediated reaction, cyclization onto unactivated pi-systems. The reactive radical intermediate is generated by the single electron reduction of an activated C-Br bond by an electron-rich redox catalyst afforded by a visible light induced catalytic cycle.

Photoredox catalysis by [Ru(bpy)3]2+ to trigger transformations of organic molecules. Organic synthesis using visible-light photocatalysis and its 20th century roots

“…Likewise, it can be anticipated that photoredox reactivity of complexes based on metals other than Ru (e.g. Ir 91 , Re 92,93 , and bimetallic photocatalysts 94 ) will also be intensively explored, as indicated by the current shift of interest to Ir photocatalysts in the recent work of MacMillan 55,56 and Stephenson 62,63,65 . Additionally, transformations triggered by purely organic photoredox catalysts start to attract attention as highlighted in the report by Zeitler group 8,95 .…”

“…A radical cyclization onto unactivated π-systems, which counts as a classic free radical mediated reaction, has been initiated by photoredox catalysis under mild conditions using Ru-as well as Ir-based photocatalysts and Et 3 N as a reductive quencher of the catalyst excited state (Schemes 51 and 52) 62 .…”

Visible light sensitive photoinitiating systems: Recent progress in cationic and radical photopolymerization reactions under soft conditions

“…Photochemical induced electron transfers from transition metals have gained great attentions particularly for synthetic applications (the process is called photoredox organocatalysis) [112][113][114][115][116][117][118]. The photocatalysts are mainly based on ruthenium or iridium thanks to their intense visible light absorption, long lived excited states and suitable redox potentials.…”

Engaging unactivated alkyl, alkenyl and aryl iodides in visible-light-mediated free radical reactions

“…In previous studies, we observed the intramolecular cyclization of bromomalonate-tethered p-systems via the reductive quenching of 2 (ref. 38). However, a-bromoester analogues did not undergo cyclization using 2, although they cyclized efficiently when the catalyst was replaced with 3.…”