Enabling artificial photosynthesis systems with molecular recycling: A review of photo- and electrochemical methods for regenerating organic sacrificial electron donors

• Grace A. Lowe

Beilstein J. Org. Chem. 2023, 19, 1198–1215, doi:10.3762/bjoc.19.88

• it will not be covered in this review. Most molecular components for photoreduction catalysis are not being developed or optimized with sacrificial electron donors that can be recycled. This means that the conditions must be reoptimized if redox mediators or other recyclable donors need to be used to

• donors used in photoreduction catalysis for artificial photosynthesis. Specifically, organic electron or hydride donors usually applied in molecular photocatalysis. 2. Survey the literature from different fields and present a sample of potentially recyclable electron donors for artificial photosynthesis

• , alongside the properties important for comparing the suitability of different donors. Such a resource should hopefully help to increase adoption of recyclable donors when developing photoreduction systems for artificial photosynthesis, as well as highlight gaps where new donor compounds are required. Review

Vicinal ketoesters – key intermediates in the total synthesis of natural products

• Marc Paul Beller and
• Ulrich Koert

Beilstein J. Org. Chem. 2022, 18, 1236–1248, doi:10.3762/bjoc.18.129

• ) [25]. Intramolecular photoreduction of an α-ketoester in the synthesis of (rac)-isoretronecanol (69) [26]. α-Ketoester as nucleophile in a Tsuji–Trost reaction in the synthesis of (rac)-corynoxine (76) [27]. Mannich reaction of an α-ketoester in the synthesis of (+)-gracilamine (83) [28

Controlled decomposition of SF₆ by electrochemical reduction

• Sébastien Bouvet,
• Bruce Pégot,
• Stéphane Sengmany,
• Erwan Le Gall,
• Eric Léonel,
• Anne-Marie Goncalves and
• Emmanuel Magnier

Beilstein J. Org. Chem. 2020, 16, 2948–2953, doi:10.3762/bjoc.16.244

• expensive methods requiring a large input of energy (high temperature, high pressure). Many SF6 decomposition strategies so far developed use photoreduction, plasma discharges or even photolysis processes [10][11]. Beyond the energetic high cost of such processes, they produce side products that are highly

Dawn of a new era in industrial photochemistry: the scale-up of micro- and mesostructured photoreactors

• Emine Kayahan,
• Mathias Jacobs,
• Leen Braeken,
• Leen C.J. Thomassen,
• Simon Kuhn,
• Tom van Gerven and
• M. Enis Leblebici

Beilstein J. Org. Chem. 2020, 16, 2484–2504, doi:10.3762/bjoc.16.202

• photoreactor. The main reasons for this increase was the high surface-area-to-volume ratio and better illumination of the monolithic photoreactor [56]. The monolithic photoreactor was shown to have a higher yield for the CO2 photoreduction compared to a cell-type reactor that had no channels. This was

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

Photophysics and photochemistry of NIR absorbers derived from cyanines: key to new technologies based on chemistry 4.0

• Bernd Strehmel,
• Christian Schmitz,
• Ceren Kütahya,
• Yulian Pang,
• Anke Drewitz and
• Heinz Mustroph

Beilstein J. Org. Chem. 2020, 16, 415–444, doi:10.3762/bjoc.16.40

Self-assembled coordination thioether silver(I) macrocyclic complexes for homogeneous catalysis

• Zhen Cao,
• Aline Lacoudre,
• Cybille Rossy and
• Brigitte Bibal

Beilstein J. Org. Chem. 2019, 15, 2465–2472, doi:10.3762/bjoc.15.239

• for gold(III) chloride whose photoreduction to gold(I) was fast and controlled [44][45]. These gold complexes at different oxidation states showed efficient catalytic properties, that were highlighted in a one-pot cascade synthesis of 4H-benzoquinolizin-4-one. Now, we propose to investigate a rigid

Bioinspired cobalt cubanes with tunable redox potentials for photocatalytic water oxidation and CO₂ reduction

• Zhishan Luo,
• Yidong Hou,
• Jinshui Zhang,
• Sibo Wang and
• Xinchen Wang

Beilstein J. Org. Chem. 2018, 14, 2331–2339, doi:10.3762/bjoc.14.208

• increase of electron-withdrawing ability of the ligand. In this case, 1-OMe exhibits the highest CO2 photoreduction activity with a CO evolution rate of 38.5 μmol·h−1, together with a H2 generation rate of 83 μmol·h−1. The CO2-to-CO conversion rate of 1-OMe is 2.5-fold enhanced than that of 1-CN (13.8

Photocatalytic formation of carbon–sulfur bonds

• Alexander Wimmer and
• Burkhard König

Beilstein J. Org. Chem. 2018, 14, 54–83, doi:10.3762/bjoc.14.4

• photocatalytically generated thiyl radical to give the C–S cross-coupling product. The same group reported on a photoredox-catalyzed approach for the difluoromethylation of thiophenols, again applying [fac-Ir(ppy)3] as photocatalyst (Scheme 20) [51]. Herein, they describe a single-electron photoreduction of readily

• diazonium salts and dimethyl disulfide (Scheme 37) [72]. They applied Eosin Y for the photoreduction of aryl diazonium salts, in order to generate the respective aryl radicals. Radical addition to the nucleophilic disulfide forms a stabilized trivalent sulfur-centred radical. Oxidation of this intermediate

• selenosulfonates Formation of sulfone derivatives Already in 1994, the group of Barton envisioned that the photoreduction of selenosulfonates by [Ru(bpy)3]Cl2 as photoredox catalyst could lead to reactive sulfonyl radicals (Scheme 50) [87]. They were the first to report on a visible-light induced sulfonylation of

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

• result of electron paramagnetic resonance spectroscopy experiments (Scheme 50). In 2016, Li, Mi and co-workers reported a simple and clean approach for the direct trifluoromethylation of unactivated arenes and heteroarenes through a photoreduction without any metal catalyst nor oxidant. The radical

Effective ascorbate-free and photolatent click reactions in water using a photoreducible copper(II)-ethylenediamine precatalyst

• Redouane Beniazza,
• Natalia Bayo,
• Florian Molton,
• Carole Duboc,
• Stéphane Massip,
• Nathan McClenaghan,
• Dominique Lastécouères and
• Jean-Marc Vincent

Beilstein J. Org. Chem. 2015, 11, 1950–1959, doi:10.3762/bjoc.11.211

• , has been synthesized and characterized by different techniques including single crystal X-ray diffraction. Highly efficient photoreduction was demonstrated when solutions of 1 in hydrogen atom donating solvents, such as THF or MeOH, were exposed to UVA radiation (350–400 nm) provided by a low pressure

• mercury lamp (type TLC = thin-layer chromatography, 365 nm), or by a 23 W fluorescent bulb, or by ambient/sunlight. In water, a much poorer hydrogen atom donating solvent, the photoreduction of 1 proved inefficient. Interestingly, EPR studies revealed that complex 1 could nonetheless be effectively

• photogenerated copper(I) being very reactive. On irradiating aqueous reaction mixtures containing 1 mol % of 1 at 365 nm (TLC lamp) for 1 h, click reactions were shown to proceed to full conversion. Keywords: benzophenone photosensitizer; bioconjugation; click chemistry; copper; photoreduction; Introduction

Photocatalytic nucleophilic addition of alcohols to styrenes in Markovnikov and anti-Markovnikov orientation

• Martin Weiser,
• Sergej Hermann,
• Alexander Penner and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2015, 11, 568–575, doi:10.3762/bjoc.11.62

• LEDs (250 mW), λ = 530 nm. Photooxidation of the substrate and reductive quenching of the photocatalyst (left) vs photoreduction of the substrate and oxidative quenching of the photocatalyst (right) give two complementary photocatalytic cycles yielding either anti-Markovnikov-type or Markovnikov-type

An integrated photocatalytic/enzymatic system for the reduction of CO₂ to methanol in bioglycerol–water

• Michele Aresta,
• Angela Dibenedetto,
• Tomasz Baran,
• Antonella Angelini,
• Przemysław Łabuz and
• Wojciech Macyk

Beilstein J. Org. Chem. 2014, 10, 2556–2565, doi:10.3762/bjoc.10.267

• NADH photoregeneration process when compared to the [CrF5(H2O)]2−@TiO2 photocatalyst. As mentioned above, glycerol was considered as an electron donor in aqueous solution. When only water was used in the photoreduction, the reaction rate was very low due to the weak ability of H2O to transfer electrons

• )(H2O)]2+ solution as a function of the applied potential (left). Cyclic voltammogram and corresponding changes in absorbance recorded at 521 nm (right). For simplicity, only the part of the potential scan (the reduction process from −0.4 to −1.4 V and back) is shown. Photoreduction of NAD+ as a

Photo, thermal and chemical degradation of riboflavin

• Muhammad Ali Sheraz,
• Sadia Hafeez Kazi,
• Sofia Ahmed,
• Zubair Anwar and
• Iqbal Ahmad

Beilstein J. Org. Chem. 2014, 10, 1999–2012, doi:10.3762/bjoc.10.208

• ns [60] and 1 ms [61], respectively. The reactions involved in the photochemical degradation of RF include photoreduction, photoaddition and photodealkylation. These reactions may occur intramolecularly or intermolecularly or often simultaneously [18][23][25][30][46][47][49][62]. However, a clear

• ]. Anaerobic photobleaching of RF in the absence of an added electron donor has been investigated by Holmström and Oster [81]. The anaerobic irradiation of RF causes intramolecular photoreduction of the isoalloxazine ring which leads to the fading of yellow color. However, if air is introduced into the

• partially irradiated solutions, the yellow color of RF may return to some extent due to the reoxidation of the isoalloxazine ring. The amount of color restored depends on the time of irradiation as little color will return with more photoreduction due to photodegradation of RF [15][81][82]. Anaerobic

Flow photochemistry: Old light through new windows

• Jonathan P. Knowles,
• Luke D. Elliott and
• Kevin I. Booker-Milburn

Beilstein J. Org. Chem. 2012, 8, 2025–2052, doi:10.3762/bjoc.8.229

• conversion at the expense of increased dimer formation, both effects being ascribed to the greater average photon density in the flow system [70]. Mechanistic studies of the photoreduction of benzophenone (63) with benzhydrol (64) (Scheme 20) have been performed in a microflow reactor, allowing the quantum

Synthesis and photooxidation of styrene copolymer bearing camphorquinone pendant groups

• Branislav Husár,
• Norbert Moszner and
• Ivan Lukáč

Beilstein J. Org. Chem. 2012, 8, 337–343, doi:10.3762/bjoc.8.37

• macroradicals leads to an increase of the molecular weight and polydispersity. As previously shown, oxygen increases the consumption rate of CQ added to PS and lowers the rate of decrease of the molecular weight of PS [22]. Therefore in simultaneous photooxidation and photoreduction (Scheme 4) in the presence

• of oxygen, the intramolecular photooxidation of CQ has almost no effect on the molecular weight [21]. In the case of MCQ/S, photoreduction forms macroradicals that recombine causing an increase in the molecular weight. Conclusion Upon irradiation of MCQ/S copolymer film by light with λ > 380 nm in

Microphotochemistry: 4,4'-Dimethoxybenzophenone mediated photodecarboxylation reactions involving phthalimides

• Oksana Shvydkiv,
• Kieran Nolan and
• Michael Oelgemöller

Beilstein J. Org. Chem. 2011, 7, 1055–1063, doi:10.3762/bjoc.7.121

• photoreduction nor photopinacolization products were detectable in the crude reaction mixture [41]. An attempt was made to isolate pure 2 by column chromatography but it eluted together with DMBP. The α-photodecarboxylation is, however, known to proceed with high selectivity [40]. Photodecarboxylative

• after 1 h of irradiation. Partial photoreduction of DMBP (ca. 10%) was furthermore observed. Using the same residence time, the transformation under microflow condition furnished a conversion to 10 of 96% but showed no decomposition of the mediator DMBP. Compound 10 could not be isolated in pure form

• but its NMR data was identical to that of an independently synthesized sample [49]. Likewise, the addition of potassium 2-(methylthio)acetate (11) to N-methylphthalimide (2) was investigated [50]. In the larger Rayonet (batch) reactor, the photoreduction product of N-methylphthalimide, i.e., compound

Synthesis of rigidified flavin–guanidinium ion conjugates and investigation of their photocatalytic properties

• Harald Schmaderer,
• Mouchumi Bhuyan and
• Burkhard König

Beilstein J. Org. Chem. 2009, 5, No. 26, doi:10.3762/bjoc.5.26

• the presence of sacrificial electron donor substrates, such as aliphatic amines, flavins can photoreduce nitro arenes to anilines under blue light irradiation (Scheme 4). 4-Nitrophenyl phosphate was used as a substrate for photoreduction in water and in acetonitrile. The results summarized in Table 2

• )2, mono-Boc guanidine, CH2Cl2, rt, 20 h, 58–82%, (iii) HCl/Et2O, CH2Cl2/CHCl3, rt, 24 h, 83–90%. Oxidative photocleavage of dibenzyl phosphate. Photoreduction of 4-nitrophenyl phosphate. Photo Diels–Alder-reaction of anthracene with N-methyl-maleinimide. Oxidative photocleavage of dibenzyl phosphate

• . Results of nitrobenzene photoreduction. Results of photoinduced Diels–Alder-reaction. Supporting Information Photocatalytic experiments, UV/Vis and fluorescence spectra of 1–3, calculated gas phase conformations, 1H and 13C NMR spectra of 1, 2, 6, 7, 9, and 10. Supporting Information File 33