Photochemical Michael reaction of silyl enol ethers with 2′-nitro- and 2′,2′-dicyanostyrenes

Ramkumar, D.; Sankararaman, S.

doi:10.1039/p29960000939

Cited by 4 publications

(4 citation statements)

References 26 publications

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“…In more recent work, pyrex-filtered irradiation was used to study the reaction of nitrostyrenes with silyl enol ethers. 15 16…”

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confidence: 99%

“…In more recent work, pyrex-filtered irradiation was used to study the reaction of nitrostyrenes with silyl enol ethers. 15,16 Inspection of the UV-Vis spectrum 17 of trans-β-nitrostyrene in CH 2 Cl 2 (Figure 1) reveals a strong absorption centered at λ = 312 nm (ε = 16500 M -1 cm -1 ). This band has been previously assigned to an allowed ππ*-transition with significant charge-transfer character.…”

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confidence: 99%

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Intermolecular [2+2] Photocycloaddition of β-Nitrostyrenes to Olefins upon Irradiation with Visible Light

Mohr¹,

Bach²

2017

Synlett

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The title compounds were found to undergo a [2+2] photocycloaddition with olefins at λ = 419 nm in CH 2 Cl 2 as the solvent. The resulting cyclobutanes were isolated in yields of 32-87% (11 examples) and showed a defined relative configuration at C1/C4 in the major diastereoisomer (nitro and aryl trans). The analysis of side products and triplet sensitization experiments support a mechanistic scenario in which a 1,4-diradical is formed as a key intermediate. cycloaddition, cyclobutanes, diastereoselectivity, nitro compounds, photochemistry, stereoselective synthesis, umpolung, visible light Although [2+2] photocycloaddition chemistry 1 originates historically 2 from experiments performed with visible light, the advent of artificial UV light sources led -starting in the middle of the 20 th century -to the almost exclusive use of short-wavelength (λ = 250-380 nm) irradiation in all areas of photochemistry. Interest in reactions that were promoted by long-wavelength (λ > 380 nm) irradiation was spurred in the 1970s and in the 1980s by the desire to find suitable energy storage systems mainly based on the [2+2] photocycloaddition of norbornadienes to quadricyclenes. 3 Aromatic carbonyl compounds 4 and transition-metal salts 5 were found to act as triplet sensitizers in this transformation allowing the reaction to occur with visible light. More recently, triplet energy sensitization has been employed for enantioselective 6 [2+2] photocycloaddition reactions that are promoted by visible light 7 in the presence of an appropriate sensitizer. 8 In the context of our work on the activation of chromophors by Lewis or Brønsted acids, 9 we became interested in the photochemistry of nitrostyrenes. 10 The compound class seemed amenable to un- (2a) to form cyclobutane 3a (Scheme 1). 14 A high-pressure mercury lamp was employed as the light source in this transformation. In more recent work, pyrex-filtered irradiation was used to study the reaction of nitrostyrenes with silyl enol ethers. 15,16 Inspection of the UV-Vis spectrum 17 of trans-β-nitrostyrene in CH 2 Cl 2 (Figure 1) reveals a strong absorption centered at λ = 312 nm (ε = 16500 M -1 cm -1 ). This band has been previously assigned to an allowed ππ*-transition with significant charge-transfer character. 18,19 At high concentration it is evident that the absorption continues into the visible region of the electromagnetic spectrum in line with the fact that trans-β-nitrostyrene (1) is a yellow-colored solid. Key words

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“…In more recent work, pyrex-filtered irradiation was used to study the reaction of nitrostyrenes with silyl enol ethers. 15 16…”

mentioning

confidence: 99%

mentioning

confidence: 99%

Intermolecular [2+2] Photocycloaddition of β-Nitrostyrenes to Olefins upon Irradiation with Visible Light

Mohr¹,

Bach²

2017

Synlett

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“…The fact that silyl enol ethers gave cyclobutanes 3g and 3h as the only isolable products was surprising. In previous photochemical studies, 8 Michael addition products were observed suggesting an addition reaction of the silyl enol ether with opposite regioselectivity. For comparison, we prepared the Michael addition product of 1-(trimethylsilyloxy)cyclopentene and trans-β-nitrostyrene by a thermal reaction.…”

Section: Reaction Scopementioning

confidence: 90%

“…It should be noted that different irradiation conditions (λ > 250 nm) and a different substrate stoichiometry (1a : silyl enol ether = 1 : 1) were used by Ramkumar and Sankararaman in their experiments. 8 Still, it remains open why the regioselectivity should be completely reverted (vide infra). In all [2 + 2] photocycloaddition products 3 the better donor substituent of the former olefin is positioned at carbon atom C2 relative to carbon atom C4 which carries the nitro group.…”

Section: Reaction Scopementioning

confidence: 99%

Visible light-mediated intermolecular [2 + 2] photocycloaddition of 1-aryl-2-nitroethenes and olefins

et al. 2019

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ChemInform Abstract: Photochemical Michael Reaction of Silyl Enol Ethers with 2′‐Nitro‐ and 2′,2′‐Dicyanostyrenes.

Ramkumar

Sankararaman

1996

ChemInform

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Photochemical Michael reaction of silyl enol ethers with 2′-nitro- and 2′,2′-dicyanostyrenes

Cited by 4 publications

References 26 publications

Intermolecular [2+2] Photocycloaddition of β-Nitrostyrenes to Olefins upon Irradiation with Visible Light

Intermolecular [2+2] Photocycloaddition of β-Nitrostyrenes to Olefins upon Irradiation with Visible Light

Visible light-mediated intermolecular [2 + 2] photocycloaddition of 1-aryl-2-nitroethenes and olefins

ChemInform Abstract: Photochemical Michael Reaction of Silyl Enol Ethers with 2′‐Nitro‐ and 2′,2′‐Dicyanostyrenes.

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