Mechanisms of photochemical reactions in solution. LXVII. Energy wastage in photosensitized isomerization of the stilbenes

Valentine, Donald; Hammond, George S.

doi:10.1021/ja00765a032

“…The absence of reaction with Ir(ppy)3 (tris[2-phenylpyridinato-C 2 ,N]iridium(III)), which has a similar triplet energy to 9fluorenone (ET = 55.3 kcal mol -1 for fluorenone vs 55.6 kcal mol -1 for Ir(ppy3)), indicates that 9-fluorenone acts as a HAT agent, and not as an energy transferring photosensitizer (Scheme 33b). [90], [91], [92] With this protocol, either the monofluorinated or gemdifluorinated products could be obtained selectively, depending on which photosensitizer and which fluorine source is used. Using 9-fluoreneone and Selectfluor, exclusive monofluorination was observed.…”

Section: Photocatalytic Methodsmentioning

confidence: 99%

The Fluorination of C−H Bonds: Developments and Perspectives

Szpera

¹

,

Moseley

²

,

Smith

³

et al. 2019

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This Review summarizes the advances in fluorination via C(sp 2)-H and C(sp 3)-H activation. Transition metal catalyzed approaches championed by palladium have allowed the installation of a fluorine substituent at C(sp 2) and C(sp 3) sites exploiting the reactivity of high oxidation transition metal fluoride complexes combined with the use of directing group (some transient) to control regio-and stereoselectivity. The large majority of known methods employ electrophilic fluorination reagents, but methods combining a nucleophilic fluoride source with an oxidant have appeared. A number of ligands have proven to be effective for C(sp 3)-H fluorination directed by weakly coordinating auxiliaries, thereby enabling control over reactivity and selectivity. Methods relying on the formation of radical intermediates are complementary to transition metal catalyzed processes as they allow for undirected C(sp 3)-H fluorination. To date, radical C-H fluorinations mainly employ electrophilic N-F fluorination reagents but a unique bio-inspired Mn(III)-catalyzed oxidative C-H fluorination has been developed. Overall, the field of late stage nucleophilic C-H fluorination has progressed much more slowly, a state of play explaining why C-H 18 F-fluorination is still in its infancy. C-F reductive elimination C(sp 2)-H C(sp 3)-H C(sp 3)-H

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“…Energietransfer-Photosensibilisator (Schema 34 b). [92][93][94] Sowohl mono-als auch gem-difluorierte Produkte wurden selektiv gebildet, je nach eingesetztem Sensibilisator und Fluorierungsreagenz:M it 9-Fluoreneon und Selectfluor wurde auschließlich Monofluorierung beobachtet. Mit zunehmender Reaktionsdauer und Menge an Selectfluor steigerte sich die Ausbeute nur vernachlässigbar.M ithilfe des elektronenreicheren Photosensibilisators Xanthon zusammen mit Selectfluor II wurde hingegen glatt eine gem-Difluorierung erreicht.…”

Section: Angewandte Chemieunclassified

Fluorierung von C‐H‐Bindungen: Entwicklungen und Perspektiven

Szpera

¹

,

Moseley

²

,

Smith

³

et al. 2019

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This Review summarizes the advances in fluorination via C(sp 2)-H and C(sp 3)-H activation. Transition metal catalyzed approaches championed by palladium have allowed the installation of a fluorine substituent at C(sp 2) and C(sp 3) sites exploiting the reactivity of high oxidation transition metal fluoride complexes combined with the use of directing group (some transient) to control regio-and stereoselectivity. The large majority of known methods employ electrophilic fluorination reagents, but methods combining a nucleophilic fluoride source with an oxidant have appeared. A number of ligands have proven to be effective for C(sp 3)-H fluorination directed by weakly coordinating auxiliaries, thereby enabling control over reactivity and selectivity. Methods relying on the formation of radical intermediates are complementary to transition metal catalyzed processes as they allow for undirected C(sp 3)-H fluorination. To date, radical C-H fluorinations mainly employ electrophilic N-F fluorination reagents but a unique bio-inspired Mn(III)-catalyzed oxidative C-H fluorination has been developed. Overall, the field of late stage nucleophilic C-H fluorination has progressed much more slowly, a state of play explaining why C-H 18 F-fluorination is still in its infancy. C-F reductive elimination C(sp 2)-H C(sp 3)-H C(sp 3)-H

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“…BZ is a well-known sensitizer that has a tripletstate energy (E T ) value of 69 kcal mol Ϫ1 and brings about the triplet-state (T 1 ) of the substrates by energy transfer from the triplet state of BZ (BZ*(T 1 )). [44][45][46][47][48][49] The E T value of 5a was estimated to be 61 kcal mol Ϫ1 from its phosphorescence spectra in a frozen MeCN/H 2 O. Upon photoirradiation of a mixture of 1 mM of 5a and 10 mM of BZ in CD 3 CN/D 2 O (10 mM HEPES at pD 7.4) (90/10) for 15 min at 355 nm, which is absorbed only by BZ, photolysis of 5a proceeded in ca.…”

Section: Chart 3 Chartmentioning

confidence: 99%

Photochemical Cleavage Reactions of 8-Quinolinyl Sulfonates in Aqueous Solution

Kageyama

¹

,

Ohshima

²

,

Sakurama³

et al. 2009

CHEMICAL & PHARMACEUTICAL BULLETIN

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Photochemical cleavage reactions of 8-quinolinyl benzenesulfonate derivatives and related sulfonates in aqueous solutions are reported. The 8-quinolinyl benzenesulfonates undergo photolysis upon photoirradiation at 300-330 nm to give the corresponding 8-quinolinols and benzenesulfonic acids with the production of only negligible amounts of byproducts. The effects of substituent groups of the 8-quinolinyl moiety and the benzene ring on the photolysis reactions were examined. Based on steady-state mechanistic studies using a triplet sensitizer, a triplet quencher, and electron donors, it was suggested that the photolysis proceeds mainly via the homolytic cleavage of S-O bonds in the excited triplet state.

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Mechanisms of photochemical reactions in solution. LXVII. Energy wastage in photosensitized isomerization of the stilbenes

Cited by 51 publications

References 0 publications

The Fluorination of C−H Bonds: Developments and Perspectives

The Fluorination of C−H Bonds: Developments and Perspectives

Fluorierung von C‐H‐Bindungen: Entwicklungen und Perspektiven

Photochemical Cleavage Reactions of 8-Quinolinyl Sulfonates in Aqueous Solution

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