A photo-reagent system of benzimidazoline and Ru(bpy)3Cl2 to promote hexenyl radical cyclization and Dowd–Beckwith ring-expansion of α-halomethyl-substituted benzocyclic 1-alkanones

Hasegawa, Eietsu; Tateyama, Minami; Hoshi, Tsuneaki; Ohta, Taku; Tayama, Eiji; Iwamoto, Hajime; Takizawa, Shin‐ya; Murata, Shigeru

doi:10.1016/j.tet.2014.02.078

Cited by 20 publications

(8 citation statements)

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“… Based on this potential, 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-7-methylbenzo-[ d ]imidazole, Me BIH, was identified as a potential reductant for Zr( Me PDP) 2 *. The redox potential for one-electron oxidation of Me BIH is slightly more negative (−0.16 V vs Fc +/0 in MeCN) than the one reported for BIH (−0.10 V vs Fc +/0 in MeCN), which is frequently used as a terminal reductant in photoredox reductions of organic substrates and CO 2 . Addition of Me BIH to Zr( Me PDP) 2 in THF solution lead to a significant reduction of luminescence intensity indicating quenching of the excited state (Figure S13).…”

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confidence: 86%

A Luminescent Zirconium(IV) Complex as a Molecular Photosensitizer for Visible Light Photoredox Catalysis

2016

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Titanium and zirconium complexes carrying two 2,6-bis(pyrrolyl)pyridine ligands have been synthesized and characterized. The neutral complexes Ti(PDP) and Zr(PDP) (PDP = 2,6-bis(5-methyl-3-phenyl-1H-pyrrol-2-yl)pyridine) show intense ligand-to-metal charge-transfer bands in the visible region and undergo multiple reversible redox events under highly reducing conditions. Zr(PDP) exhibits photoluminescent behavior and its excited state can be quenched by mild reductants to generate a powerful electron transfer reagent with a ground state potential of -2.16 V vs Fc. This reactivity was utilized to facilitate dehalogenation reactions, the reduction of electron-poor olefins, and the reductive coupling of benzyl bromide via photoredox catalysis. In these reactions, the earth-abundant metal complex Zr(PDP) acts as a substitute for the precious metal photosensitizer [Ru(bpy)].

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confidence: 86%

A Luminescent Zirconium(IV) Complex as a Molecular Photosensitizer for Visible Light Photoredox Catalysis

2016

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“…8b However, as we previously discussed, deprotonation of the benzimidazoline radical cation could occur if the coproduced substrate radical anion is sufficiently basic. 32 In any event, it is expected that the nonhydroxyaryl-substituted benzimidazoline 1f would be oxidized during its reaction with 2a by a sequence involving HAT as shown in Scheme 5. In addition, the radical anion of 2a is expected to undergo efficient fragmentation to form α-ketoalkyl radical 7a in a route that does not require an initial PT step.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…According to Zhu’s pioneering work, thermodynamic considerations suggest that radical cations of 2-arylbenzimidazolines (BIH-Ar) should more readily undergo hydrogen atom donation than deprotonation from the C 2 position because the resulting cations are much more stable than the corresponding radicals . However, as we previously discussed, deprotonation of the benzimidazoline radical cation could occur if the coproduced substrate radical anion is sufficiently basic . In any event, it is expected that the nonhydroxyaryl-substituted benzimidazoline 1f would be oxidized during its reaction with 2a by a sequence involving HAT as shown in Scheme .…”

Section: Resultsmentioning

confidence: 99%

Competitive Desulfonylative Reduction and Oxidation of α-Sulfonylketones Promoted by Photoinduced Electron Transfer with 2-Hydroxyaryl-1,3-dimethylbenzimidazolines under Air

et al. 2021

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Desulfonylation reactions of α-sulfonylketones promoted by photoinduced electron transfer with 2-hydroxyarylbenzimidazolines (BIH-ArOH) were investigated. Under aerobic conditions, photoexcited 2hydroxynaphthylbenzimidazoline (BIH-NapOH) promotes competitive reduction (forming alkylketones) and oxidation (producing α-hydroxyketones) of sulfonylketones through pathways involving the intermediacy of α-ketoalkyl radicals. The results of an examination of the effects of solvents, radical trapping reagents, substituents of sulfonylketones, and a variety of hydroxyaryl-and aryl-benzimidazolines (BIH-ArOH and BIH-Ar) suggest that the oxidation products are produced by dissociation of α-ketoalkyl radicals from the initially formed solvent-caged radical ion pairs followed by reaction with molecular oxygen. In addition, the observations indicate that the reduction products are generated by proton or hydrogen atom transfer in solvent-caged radical ion pairs derived from benzimidazolines and sulfonylketones. The results also suggest that arylsulfinate anions arising by carbon-sulfur bond cleavage of sulfonylketone radical anions act as reductants in the oxidation pathway to convert initially formed α-hydroperoxyketones to α-hydroxyketones. Finally, density functional theory calculations were performed to explore the structures and properties of radical ions of sulfonylketones as well as BIH-NapOH.

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“…Substrates 1a , 1b , 1c , 1e , 1f , and 1g and products 1a -OH, 1b -OH, 1c -OH, 2g , 3a , 3c , 5a , 5b , 5c , 5f , 5g , 6a , 6e , 7b , 7c , 16 , 19 , 20 , 24 , 25 , 26 , 27 , and 29 are known compounds. 1 H NMR and 13 C NMR charts of 1d , 1d -OH, 1f -OH, 2a , 2c , 2d , 2e , 3d , 6b , 6c , 6f , 6g , 7a , 7e , 7f , 7g , 8a , 9a , 10a , 21 , and 28 are presented below.…”

Section: Methodsmentioning

confidence: 99%

Solvent-Dependent Reaction Pathways Operating in Copper(II) Tetrafluoroborate Promoted Oxidative Ring-Opening Reactions of Cyclopropyl Silyl Ethers

et al. 2016

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Oxidative ring-opening reactions of benzene-fused bicyclic cyclopropyl silyl ethers, promoted by copper(II) tetrafluoroborate, were investigated. The regioselectivity of cyclopropane ring-opening as well as product distributions were found to be highly dependent on the nature of the solvent. In alcohols, dimeric substances arising from external bond cleavage are major products. Radical rearrangement products are also formed in solvents such as ether and ethyl acetate. On the contrary, nucleophile addition to carbocation intermediates, generated by internal bond cleavage, occurs mainly in reactions taking place in acetonitrile. It is proposed that the observed solvent effects that govern the reaction pathways followed are a consequence of varying solvation of copper intermediates, which governs their reactivity and redox properties. In addition, the influence of counteranions of the copper salts, organonitriles, cyclic dienes, and substrate structures on the pathways followed in these reactions was also examined.

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A photo-reagent system of benzimidazoline and Ru(bpy)3Cl2 to promote hexenyl radical cyclization and Dowd–Beckwith ring-expansion of α-halomethyl-substituted benzocyclic 1-alkanones

Cited by 20 publications

References 100 publications

A Luminescent Zirconium(IV) Complex as a Molecular Photosensitizer for Visible Light Photoredox Catalysis

A Luminescent Zirconium(IV) Complex as a Molecular Photosensitizer for Visible Light Photoredox Catalysis

Competitive Desulfonylative Reduction and Oxidation of α-Sulfonylketones Promoted by Photoinduced Electron Transfer with 2-Hydroxyaryl-1,3-dimethylbenzimidazolines under Air

Solvent-Dependent Reaction Pathways Operating in Copper(II) Tetrafluoroborate Promoted Oxidative Ring-Opening Reactions of Cyclopropyl Silyl Ethers

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