Mechanistische Studien in der Photokatalyse

Buzzetti, Luca; Crisenza, Giacomo E. M.; Melchiorre, Paolo

doi:10.1002/ange.201809984

Cited by 122 publications

(17 citation statements)

References 135 publications

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“…On the basis of the above-mentioned results and the previous literature, ,,,− a possible mechanism for the production of 5aa under the Cu(I)-photoredox catalysis conditions is proposed in Scheme . Upon irradiation with blue light, the Cu(I)-based PS5 was excited to its excited state Cu(I)* ( E 1/2 [Cu I* /Cu 0 ] = 1.04 V versus SCE (saturated calomel electrode) in MeCN, see SI), which was quenched by dipropylamine 3c ( E p/2 [( n -Pr) 2 NH •+ /( n -Pr) 2 NH] = 0.89 V vs SCE in MeCN, see SI; literature value: E p [( n -Pr) 2 NH •+ /( n -Pr) 2 NH] = 0.90 V vs SCE) and/or Hantzsch ester 4 ( E [( HE •+ / HE ] = 0.79 V vs SCE; E[( HE •+ )/ HE *] = −2.28 V vs SCE) through an SET process, , leading to the generation of dipropylamine radical cation species 3c′ and/or Hantzsch ester radical cation species 4′ , and the reactive Cu(0) complex. The above quenching processes were further confirmed by Stern–Volmer studies (see Figures S13 and S14 in SI).…”

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confidence: 79%

P/N Heteroleptic Cu(I)-Photosensitizer-Catalyzed Deoxygenative Radical Alkylation of Aromatic Alkynes with Alkyl Aldehydes Using Dipropylamine as a Traceless Linker Agent

et al. 2020

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A deoxygenative radical alkylation of aromatic alkynes with alkyl aldehydes for the preparation of allylarenes has been successfully achieved. This transformation is accomplished through the reaction of alkyl aldehydes with alkynes in the presence of dipropylamine and Hantzsch ester catalyzed by a P/N heteroleptic Cu(I)-based photosensitizer under photoredox catalysis conditions. Preliminary mechanistic studies reveal that this aldehyde–alkyne coupling process comprises a regioselective radical addition of in situ-generated alkyl-substituted α-amino radicals to alkynes with subsequent 1,5-proton transfer, C–N bond cleavage, and concomitant isomerization of the resulting allyl radical species. Thus, in net result, dipropylamine serves as a traceless linker agent for the deoxygenative radical cross-coupling of alkyl aldehydes with alkynes under photoredox catalysis reaction conditions.

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confidence: 79%

P/N Heteroleptic Cu(I)-Photosensitizer-Catalyzed Deoxygenative Radical Alkylation of Aromatic Alkynes with Alkyl Aldehydes Using Dipropylamine as a Traceless Linker Agent

et al. 2020

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“…To learn about the mode of action of the photocatalyst and to understand other mechanistic details, several spectrophotometric experiments were performed. [31] In the beginning, fluorescence emission spectra of the photocatalyst in the presence of different reactions components (1 a, 2 a, 4 a, 6 a and K 2 HPO 4 ) were recorded and analyzed in detail to estimate the light emission properties of the pure catalyst system and the distractions by external interferences (see SI for more details). The Stern-Volmer plot was depicted based on the photoluminescence quenching of the [a] Reaction conditions: 1 (0.3 mmol), 6 (0.3 mmol), AOBHZn…”

Section: Table 3 Substrate Scope Of Sulfonylation Reaction [Ab]mentioning

confidence: 99%

Acridine Orange Hemi(Zinc Chloride) Salt as a Lewis Acid‐Photoredox Hybrid Catalyst for the Generation of α‐Carbonyl Radicals

2021

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A readily accessible organic‐inorganic hybrid catalyst is reported for the reductive fragmentation of α‐halocarbonyl compounds. The robust hybrid catalyst is a self‐stabilizing combination of ZnCl2 Lewis acid and acridine orange as the photoactive organic dye. Mechanistic specifics of this hybrid catalyst have been studied in detail using both photophysical and electrochemical experiments. A systematic study enabled the discovery of the appropriate Lewis acid for the effective LUMO stabilization of α‐halocarbonyl compounds and thereby lowering of reduction potential within the range of a standard organic dye. This strategy resolves the issues like dehalogenative hydrogenation or homo‐coupling of alkyl radicals by guiding the photoredox cycle through an oxidative quenching pathway. The cooperativity between the photoactive organic dye and the Lewis acid counterparts empowers functionalization with a wide range of coupling partners through efficient and controlled generation of alkyl radicals and serves as an appropriate alternative to the expensive late transition metal‐based photocatalysts. To demonstrate the application potential of this cooperative catalytic system, four different synthetic transformations of α‐carbonyl bromides were explored with broad substrate scopes.

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“…A systematic survey of reaction conditions allowed us to identify the following optimum conditions: fac-Ir(ppy) 3 (1.0 mol %) as a photoredox catalyst in dichloromethane (DCM) under irradiation with blue LEDs at room temperature (Table 1, entry 1). [25] Under these conditions, the 1,2aminoisothiocyanation product 3 a was formed as single isomer in 75 % isolated yield. While 3 a was formed in similar yield with Ir(ppy) 2 (dtbbpy)(PF 6 ) (entry 2), other commonly used photocatalysts, such as Ru(bpy) 3 Cl 2 •6 H 2 O and eosin Y, gave inferior results (entries 2-4).…”

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confidence: 94%

Selective 1,2‐Aminoisothiocyanation of 1,3‐Dienes Under Visible‐Light Photoredox Catalysis

2020

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Selective three‐component 1,2‐diamination of 1,3‐dienes with concurrent introduction of two orthogonally protected amino groups remains unknown despite its significant synthetic potential. We report herein that reaction of conjugated dienes with N‐aminopyridinium salts and TMSNCS affords 1,2‐aminoisothiocyanation products in a highly chemo‐ and regio‐selective manner under mild photoredox catalytic conditions. Mechanistic studies indicate that the facile isomerization of allyl thiocyanates to allyl isothiocyanates under photocatalytic conditions is responsible for the selective formation of the observed products. The mild isomerization protocol is expected to find applications in the synthesis of allyl isothiocyanates in a broad sense.

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Mechanistische Studien in der Photokatalyse

Cited by 122 publications

References 135 publications

P/N Heteroleptic Cu(I)-Photosensitizer-Catalyzed Deoxygenative Radical Alkylation of Aromatic Alkynes with Alkyl Aldehydes Using Dipropylamine as a Traceless Linker Agent

P/N Heteroleptic Cu(I)-Photosensitizer-Catalyzed Deoxygenative Radical Alkylation of Aromatic Alkynes with Alkyl Aldehydes Using Dipropylamine as a Traceless Linker Agent

Acridine Orange Hemi(Zinc Chloride) Salt as a Lewis Acid‐Photoredox Hybrid Catalyst for the Generation of α‐Carbonyl Radicals

Selective 1,2‐Aminoisothiocyanation of 1,3‐Dienes Under Visible‐Light Photoredox Catalysis

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