Radical anion ring opening reactions via photochemically induced electron transfer

Cossy, Janine; Aclinou, P.; Bellosta, Véronique; Furet, N.; Baranne-Lafont, J.; Sparfel, D.; Souchaud, C.

doi:10.1016/s0040-4039(00)79654-7

Cited by 55 publications

(13 citation statements)

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“…[1] Nowadays, the necessity to devise ecocompatible alternatives for the generation of radical species has stimulated intense research efforts. Ring opening of a-ketoepoxides [12] has been sporadically reported under UV irradiation [13] and our goal was first to develop an alternative using low-energy visiblelight activation. For that purpose, the use of visible light and a photoredox catalyst such as [Ru(bpy) 3 ]Cl 2…”

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confidence: 99%

“…Owing to their low redox potential (À2.35 V for stilbene oxide vs. Ag/AgI) [11] compared to [Ru(bpy) 3 ] 2+ /[Ru(bpy) 3 ] + (À1.33 V vs. SCE), we quickly abandoned our initial approach based on direct electron transfer to the oxirane, but we installed an a-carbonyl moiety as a relay. Ring opening of a-ketoepoxides [12] has been sporadically reported under UV irradiation [13] and our goal was first to develop an alternative using low-energy visiblelight activation. Then, the photogenerated radical could be exploited in the context of carbon-carbon bond formation (Scheme 1).…”

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confidence: 99%

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Visible‐Light‐Induced Photoreductive Generation of Radicals from Epoxides and Aziridines

et al. 2011

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As a result of its unique features, radical chemistry has become a reliable and efficient tool for synthetic chemists over the last fifty years.[1] Nowadays, the necessity to devise ecocompatible alternatives for the generation of radical species has stimulated intense research efforts.[2] The development of single-electron transfer (SET) redox processes using catalytic amounts of metal complexes would be a significant advance. For that purpose, the use of visible light and a photoredox catalyst such as [Ru(bpy) 3 ]Cl 2[3] has lately appeared to offer very promising possibilities.[4] Thus, following the pioneering findings of Cano-Yelo and Deronzier, [5] recent contributions from the research groups of Yoon, MacMillan, and Stephenson have demonstrated that enones, [6] perfluorated iodides, [7] as well as activated chlorides and bromides [8] are suitable substrates for the formation of radicals by visible light-catalyzed reductive electron transfers.Because epoxides are exquisite substrates for radical transformations, [9] we envisioned to expand the scope of visible light photoredox catalysis to the ring opening of these moieties, and access a formal photocatalytic Nugent-RajanBabu-Gansäuer [10] reaction. Owing to their low redox potential (À2.35 V for stilbene oxide vs. Ag/AgI) [11] + (À1.33 V vs. SCE), we quickly abandoned our initial approach based on direct electron transfer to the oxirane, but we installed an a-carbonyl moiety as a relay. Ring opening of a-ketoepoxides [12] has been sporadically reported under UV irradiation [13] and our goal was first to develop an alternative using low-energy visiblelight activation. Then, the photogenerated radical could be exploited in the context of carbon-carbon bond formation (Scheme 1).[14] Our results are presented herein. Our preliminary investigation was carried out on epoxychalcone 1 a (Table 1). First, we tested the Stephenson conditions used for dehalogenation [8b] (i.e. [Ru(bpy) 3 ]Cl 2 -·(H 2 O) 6 (5 mol %), iPr 2 NEt (2 equiv), and Hantzsch ester (1.1 equiv) in DMF). After 36 hours of irradiation with a 14 W fluorescent lamp, b-hydroxyketone 2 a was obtained in 74 % yield with incomplete conversion of 1 a.A rapid solvent screening indicated that DMSO was the best solvent. Finally, it became apparent that the Hantzsch ester could be both the reductive quencher and the hydrogen and proton donor. Indeed, in a typical reduction, 1 a led to 91 % of 2 a after 3 hours of irradiation at room temperature in DMSO, in the presence of the Hantzsch ester (1.1 equiv) and [Ru(bpy) 3 ]Cl 2 ·(H 2 O) 6 (5 mol %) only. [15] Scheme 1. Photocatalytic reductive ring opening of epoxides and subsequent carbon-carbon bond formation. Yield [%] [c]

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Visible‐Light‐Induced Photoreductive Generation of Radicals from Epoxides and Aziridines

et al. 2011

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“…The radical-anion reactions of epoxides proceeding through a photochemically induced electron transfer can be cited [136,137]. By an example of 1-methyl-1,2epoxycyclohexane and other epoxides a regioselective reduction was carried out occurring by electron transfer, a new efficient photochemical method of epoxides reduction under UV irradiation (λ 254 nm) in the presence of triethylamine and sodium borohydride under a nitrogen atmosphere [136].…”

Section: Methods and Mechanisms Of Epoxy Compounds Reductionmentioning

confidence: 99%

“…The reduction takes a similar route when the epoxy ring of the molecule is conjugated with a carbonyl group in substrate 152 [137] (Scheme 75).…”

Section: Methods and Mechanisms Of Epoxy Compounds Reductionmentioning

confidence: 99%

10.1007/s11178-008-2001-z

2010

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Analysis was performed of reduction processes of epoxy derivatives obtained from unsaturated compounds belonging to various groups: alkenes, cycloalkenes, spiroalkanes, and substituted norbornenes. The regio-and stereochemistry was discussed of reactions between epoxides and complex metal hydrides, of catalytic hydrogenation, and some other processes. The mechanisms were considered of the reduction reactions, in particular, those involving radical and ion radical intermediates.

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“…Oxa-bridge opening of the 7-oxabicyclo[2.2.1]heptan-2-one unit of 24 was achieved under the photochemical reducing conditions of Cossy[25]. Irradiation of 24 in MeCN in the presence of Et 3 N (quartz irradiator, low-pressure Hg lamps) led to a Scheme…”

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Stereoselective Synthesis of 5a-Ethyl-1,2,3,3a,4,5,5a,6,9a,9b-decahydro- 1,3,4-trihydroxy-3a-(hydroxymethyl)-7H-benz[e]inden-7-one Derivatives

Mosimann

Vogel

1999

HCA

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Homochiral Diels‐Alder cyclodimerization of (±)‐6‐ethenyl‐7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐endo‐ol (1) followed by oxidation gives (1RS,4RS,4aSR,4bSR,5RS,8RS,8aRS)‐8a‐ethenyl‐1,3,4,4a,4b,5,6,8,8a,9‐decahydro‐1,4:5,8‐diepoxyphenanthrene‐2,7‐dione (18). Selective hydrogenation followed by epoxidation produced (1RS,4RS,4aRS,5aRS,6aRS,7RS,10RS,10aSR,10bRS)‐6a‐ethyl‐1,4,5a,6,6a,7,9,10,10a,10b‐decahydro‐1,4:7,10‐diepoxyphenanthro[8a,9‐b]oxirene‐3,8‐dione (21), which was solvolyzed (Me3SiOSO2CF3, Piv2O) with concomitant pinacol rearrangement involving an acyl‐group migration to give a 6‐oxo‐7‐oxabicyclo[2.2.1]hept‐2‐yl cation intermediate, which finally generated (1RS,3SR,3aRS,4SR,5aRS,6RS,9RS,9aSR,9bSR)‐5a‐ethyl‐1,4,5,5a,6,7,8,9,9a,9b‐decahydro‐7,10‐dioxo‐3H‐6,9‐epoxy‐1,3a‐ethanonaphtho[1,2‐c]furan‐3,4‐diyl bis(2,2‐dimethylpropanoate) (24). Photo‐reductive 7‐oxa bridge opening of 24, followed by water elimination and silylation, provided (1RS,3SR,3aRS,4SR,5aSR,9aSR,9bSR)‐7‐{[(tert‐butyl)dimethylsilyl]oxy}‐5a‐ethyl‐1,4,5,5a,9a,9b‐hexahydro‐10‐oxo‐3H‐1,3‐ethanonaphtho[1,2‐c]furan‐3,4‐diyl bis(2,2‐dimethylpropanoate) (34). Reduction of 34 with NaBH4 in MeOH followed by desilylation and alcohol protection produced (1RS,3RS,3aRS,4SR,5aSR,9aSR,9bSR)‐5a‐ethyl‐2,3,3a,4,5,5a,6,7,9a,9b‐decahydro‐1,3‐bis(methoxymethoxy)‐3a‐[(methoxymethoxy)methyl]‐7‐oxo‐1H‐benz[e]inden‐4‐yl 2,2‐dimethylpropanoate (5), a polyoxy‐substituted decahydro‐1H‐benz[e]indene derivative with cis‐transoid‐trans junction for the two cyclohexane and the cyclopentane rings bearing an angular 3a‐(oxymethyl) substituent.

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Radical anion ring opening reactions via photochemically induced electron transfer

Cited by 55 publications

References 8 publications

Visible‐Light‐Induced Photoreductive Generation of Radicals from Epoxides and Aziridines

Visible‐Light‐Induced Photoreductive Generation of Radicals from Epoxides and Aziridines

10.1007/s11178-008-2001-z

Stereoselective Synthesis of 5a-Ethyl-1,2,3,3a,4,5,5a,6,9a,9b-decahydro- 1,3,4-trihydroxy-3a-(hydroxymethyl)-7H-benz[e]inden-7-one Derivatives

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