Visible Light Photoredox Catalyzed Cascade Cyclizations of α‐Bromochalcones or α‐Bromocinnamates with Heteroarenes

Abstract

Vinyl radicals were generated from a-bromochalcones or a-bromocinnamate ethyl ester under visible light photoredox catalyzed conditions via an oxidative quenching cycle of the iridium complex [Ir{dFA

Iridium(III) Photocatalysis: A Visible‐Light‐Induced Dearomatizative Tandem [4+2] Cyclization to Furnish Benzindolizidines

“…6a Complementary to thermal methods, photoredox‐initiated radical additions to indoles have also been developed, but the methods reported to date have encompassed only intramolecular aromatizative cyclizations1c, 3a and intermolecular oxidative functionalizations 7. 8 We report herein a dearomatizative intermolecular photoredox annulation of indoles by way of a diastereoselective tandem [4+2] cyclization between N ‐(2‐iodoethyl)indoles and alkenes, which is terminated by a highly efficient H‐atom transfer (HAT) step.…”

Photo-induced tandem cyclization of 3-iodoflavones with electron rich five-membered heteroarenes

“…Due to the stabilization of the additional phenyl ring through the larger conjugation system, a-bromochalcone 4a gave the cyclization product in an improved yield compared to the methyl substrate 4b. Even though a similar cyclization has been reported, 15 it is important to mention that the current protocol avoids the Scheme 2 Proposed mechanism for the preparation of coupling product C.…”

“…[12][13][14] During the last decade, extensive investigations have been made on the photo-induced tandem vinyl radical cyclization, which could build multiple C-C bonds in a single step under mild conditions. [15][16][17] In 2014, O. Reiser reported a radical tandem addition-cyclization of a-bromochalcones or a-bromocinnamates with heteroarenes using an iridium complex as the catalyst and irradiating with visible light (Scheme 1, top). 15 Similarly, O. Reiser reported a visible light-mediated coupling of a-bromochalcones with alkenes under the visible-light photo-redox conditions in the presence of fac-Ir(ppy) 3 at room temperature (Scheme 1, middle).…”

“…[15][16][17] In 2014, O. Reiser reported a radical tandem addition-cyclization of a-bromochalcones or a-bromocinnamates with heteroarenes using an iridium complex as the catalyst and irradiating with visible light (Scheme 1, top). 15 Similarly, O. Reiser reported a visible light-mediated coupling of a-bromochalcones with alkenes under the visible-light photo-redox conditions in the presence of fac-Ir(ppy) 3 at room temperature (Scheme 1, middle). 16 In 2017, another transition-metal catalyzed tandem cyclization of vinyl radicals used for the synthesis of substituted indolines was developed via a photoredox-mediated reductive quenching cycle (Scheme 1, bottom).…”

Visible‐Light‐Promoted Generation of α‐Ketoradicals from Vinyl‐bromides and Molecular Oxygen: Synthesis of Indenones and Dihydroindeno[1,2‐c]chromenes

“…[1] Recently,wefound that abromochalcones can be coupled with ab road variety of electron-rich heteroarenes [2] or alkenes [3] to give polycyclic aromatic scaffolds.H owever,p hotochemical activation of vinyl halides is rare,requiring either an extended p-system or weak bonds as found in vinyl iodides. [1] Recently,wefound that abromochalcones can be coupled with ab road variety of electron-rich heteroarenes [2] or alkenes [3] to give polycyclic aromatic scaffolds.H owever,p hotochemical activation of vinyl halides is rare,requiring either an extended p-system or weak bonds as found in vinyl iodides.…”