Visible-light-mediated copper photocatalysis for organic syntheses

• Yajing Zhang,
• Qian Wang,
• Zongsheng Yan,
• Donglai Ma and
• Yuguang Zheng

Beilstein J. Org. Chem. 2021, 17, 2520–2542, doi:10.3762/bjoc.17.169

• renewable energy and green chemistry for many years. Ruthenium and iridium, which can be used as photoredox catalysts, are expensive and scarce in nature. Thus, the further development of catalysts based on these transition metals is discouraged. Alternative photocatalysts based on copper complexes are

• organic dyes and metal complexes have been investigated [10][11][12]. Photoredox catalysts have been initially applied to organic reactions, but they are now used for complicated organic processes [13]. As photocatalysts, organic dyes have the advantages of having a low price and not containing metals

• electrons from donors are relatively scarce in the literature. Thus, the RQC pathway rarely occurs for CuI-photocatalyzed reactions. Yet, CuI complexes have the potential to replace ruthenium or iridium-based photocatalysts in reductive photoredox reactions due to their strong reduction ability [22][29

Exfoliated black phosphorous-mediated CuAAC chemistry for organic and macromolecular synthesis under white LED and near-IR irradiation

• Azra Kocaarslan,
• Zafer Eroglu,
• Önder Metin and
• Yusuf Yagci

Beilstein J. Org. Chem. 2021, 17, 2477–2487, doi:10.3762/bjoc.17.164

• , we present a novel synthetic methodology for the photoinduced CuAAC reaction utilizing exfoliated two-dimensional (2D) few-layer black phosphorus nanosheets (BPNs) as photocatalysts under white LED and near-IR (NIR) light irradiation. Upon irradiation, BPNs generated excited electrons and holes on

• polymer modification by adding spatial and temporal control [12][13]. In recent years, heterogeneous photocatalysts have been performed in many photosynthetic reactions since they provide a more reasonable and easy way to synthesize the targeted products compared to the classical homogenous photocatalysts

• photocatalysts have been successfully applied in both small- and large-scale synthesis such as organic reactions [16][17], free radical polymerization (FRP) [18][19][20], controlled radical polymerization (CRP) [21][22], CuAAC chemistry [23][24][25], and thiol–ene chemistry [26][27]. However, most of the

Photoredox catalysis in nickel-catalyzed C–H functionalization

• Lusina Mantry,
• Rajaram Maayuri,
• Vikash Kumar and
• Parthasarathy Gandeepan

Beilstein J. Org. Chem. 2021, 17, 2209–2259, doi:10.3762/bjoc.17.143

• developments in the field of photoredox nickel-catalyzed C‒H functionalization reactions with a range of applications until summer 2021. Keywords: C–H activation; functionalization; nickel; photocatalysts; photoredox; visible light; Introduction During the last decades, transition-metal-catalyzed

• catalysis under blue light irradiation (Scheme 45) [128]. Among the tested several commercially available photocatalysts, Ir[dF(CF3)ppy]2(dtbbpy)PF6 was found to provide the desired products in good yields. Aldehyde C–H functionalization Inspired by their earlier contributions on HAT-metallaphotoredox

• opportunities for late-stage diversification of complex molecules. Despite the significant advances, the photoredox-mediated nickel-catalyzed C‒H functionalization is still in its infancy. Thus far, expensive iridium-based complexes are the most common photocatalysts and are essential to achieve satisfactory

Cerium-photocatalyzed aerobic oxidation of benzylic alcohols to aldehydes and ketones

• Girish Suresh Yedase,
• Sumit Kumar,
• Jessica Stahl,
• Burkhard König and
• Veera Reddy Yatham

Beilstein J. Org. Chem. 2021, 17, 1727–1732, doi:10.3762/bjoc.17.121

• thermal conditions. Significant advances were made for the oxidation of benzylic alcohols by using metal-based photocatalysts [38][39][40][41][42][43][44][45][46] and metal-free photocatalysis [47][48][49][50][51][52][53] in combination with various oxidants, such as TBHP and DDQ [54][55]. However, the

Heterogeneous photocatalytic cyanomethylarylation of alkenes with acetonitrile: synthesis of diverse nitrogenous heterocyclic compounds

• Guanglong Pan,
• Qian Yang,
• Wentao Wang,
• Yurong Tang and
• Yunfei Cai

Beilstein J. Org. Chem. 2021, 17, 1171–1180, doi:10.3762/bjoc.17.89

• photocatalysts are used; and the scope remains limited to activated alkenes. Therefore, it is still highly desirable to develop a general, efficient, and practical protocol for the cyanomethylarylation of unactivated alkenes from readily available radical initiators under mild and environmentally benign

• ]. In the last few years, carbon nitride-based heterogeneous photocatalysts have also been utilized for several other radical-initiated synthetic transformations [44][45][46][47][48][49][50][51][52][53][54][55][56]. However, to the best of our knowledge, the application of a CN-based photocatalyst for

Insight into functionalized-macrocycles-guided supramolecular photocatalysis

• Minzan Zuo,
• Krishnasamy Velmurugan,
• Kaiya Wang,
• Xueqi Tian and
• Xiao-Yu Hu

Beilstein J. Org. Chem. 2021, 17, 139–155, doi:10.3762/bjoc.17.15

• photocatalytic reaction with a rate acceleration facilitated by supramolecular host–guest interactions and hybrid materials are typically assisted by noncovalent forces, including Coulomb and van der Waals forces, hydrogen bonding, and π–π interactions. For potential supramolecular photocatalysts, they should

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

• performance dropped 17% after 6 h of operation and remained stable for the next 19.5 h [51]. Similarly, glass beads coated with photocatalysts were proved to increase the photoreaction rate twice in a luminescent solar concentrator (LSC) photomicroreactor with capillary channels [50]. Azam et al. studied

• combination of an oscillatory flow with the static mixers of the HANU reactor (Figure 5c) enabled a stable suspension of the photocatalysts without clogging of the reactor channels [58]. Corning flow reactors are designed to provide good mixing for multiphase reactions with periodic heart-shaped static mixers

• (a pharmaceutical micropollutant) from urban wastewater. The effect of a catalyst-coated surface and the illumination mechanism were studied. When a larger surface area was coated with the photocatalysts, the photocatalyst reactivity was increased [61]. Marinho et al. compared the performance of the

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• photocatalysts (PCs) generate excited state substrates that can then undergo reactions that would be impossible in the ground state [4]. A challenge for enantioselective catalysis is stifling the racemic background reaction, which is generally achieved through a lower activation energy for the catalysed process

• issues, with many different strategies and types of photocatalysts employed. This review aims to cover the seminal work within enantioselective photocatalysis but with a focus on the most recent developments. There have been a number of reviews on or closely related to this topic, so this review will not

• photocatalysts used for this reaction, it is proposed the excited state of 9 is sufficiently reducing to initiate the chain mechanism through an oxidative quench. Moving away from electronically activated halides, MacMillan et al. investigated a tricatalytic system, utilising enamine, photoredox, and HAT

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• excitation of the target substrate, one solution is the use of visible-light-harvesting photocatalysts that transfer their excitation energy to the target substrate. Over the last few decades, the field of visible-light photocatalysis has proven itself as a highly effective, versatile and “green” strategy

• photochemistry with near-UV behaves similar to UV photochemistry. On the other hand, photocatalysts typically used in PRC possess very high extinction coefficients, leading to a strong visible light absorption and reactions that suffer more on a scale-up due to the exponential relationship between the

When metal-catalyzed C–H functionalization meets visible-light photocatalysis

• Lucas Guillemard and
• Joanna Wencel-Delord

Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147

• photocatalyst is reoxidized to its ground state by molecular oxygen, thus closing both catalytic cycles. Remarkably, this transformation could also be efficiently performed with heterogeneous inorganic photocatalysts, as was illustrated by a reaction performed in the presence of WO3. The above-presented

Photoredox-catalyzed silyldifluoromethylation of silyl enol ethers

• Vyacheslav I. Supranovich,
• Vitalij V. Levin and
• Alexander D. Dilman

Beilstein J. Org. Chem. 2020, 16, 1550–1553, doi:10.3762/bjoc.16.126

• analyzed by 19F NMR spectroscopy. A series of typical photocatalysts (for example, iridium catalysts) were ineffective in promoting the reaction. Rewardingly, a gold catalyst, [AuCl(μ-dppm)]2 [25][26][27], provided reasonable yields of 3a after one day of irradiation along with a full conversion of the

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

• has shifted the paradigms of photochemistry, opening new avenues of research with safer and scalable processes that can be readily implemented in academia and industry. Current state-of-the-art photocatalysts are homogeneous transition metal complexes that have favourable photophysical properties

• , wide electrochemical redox potentials, and photostability. However, these photocatalysts present serious drawbacks, such as toxicity, limited availability, and the overall cost of rare transition metal elements. This reduces their long-term viability, especially at an industrial scale. Heterogeneous

• photocatalysts (HPCats) are an attractive alternative, as the requirement for the separation and purification is largely removed, but typically at the cost of efficiency. Flow chemical reactors can, to a large extent, mitigate the loss in efficiency through reactor designs that enhance mass transport and

Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

• Alessandra Del Tito,
• Havall Othman Abdulla,
• Davide Ravelli,
• Stefano Protti and
• Maurizio Fagnoni

Beilstein J. Org. Chem. 2020, 16, 1476–1488, doi:10.3762/bjoc.16.123

• (hetero)aromatic rings. Most of the protocols illustrated herein, however, involved the use of rather expensive transition-metal-based (e.g., on Ru or Ir) photocatalysts, that still represents an issue in terms of sustainability. In this context, the use of photoorganocatalysts [24] is a promising

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• Yeersen Patehebieke School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, 210023, China 10.3762/bjoc.16.118 Abstract Disulfides are versatile catalysts. They can be photocatalysts, hydrogen atom transfer (HAT) catalysts, cocatalysts, or initiators in photocatalytic reactions

Distinctive reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines under photoredox conditions

• Shrikant D. Tambe,
• Kwan Hong Min,
• Naeem Iqbal and
• Eun Jin Cho

Beilstein J. Org. Chem. 2020, 16, 1335–1342, doi:10.3762/bjoc.16.114

• the yield of the 1,2-diamine product (Table 1). Among the series of photocatalysts tested, ranging from the Ru/Ir polypyridyl complexes to organic dyes, [Ir(dtbbpy)(ppy)2]PF6 was found to be the best and afforded 2a in 60% yield, along with 11% of the homocoupled product 3a (Table 1, entries 1–9). The

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• under the action of photocatalysts [109][110], cyclization of nitroso intermediate [111], etc. [112][113]. At least some of these reactions do not involve oxime radicals as intermediates. It should be noted that free-radical cyclizations mediated by iminoxyl radicals frequently afford products that are

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• states with different classes of molecules. However, the relatively high cost of these photocatalysts, their toxicity, and the limited abundance of the coordinating transition metals can hamper their applicability [13]. For these reasons, the quest for cheaper, more sustainable, and environmentally

• benign photocatalysts is of high importance, and organic dyes represent a powerful platform for pursuing this goal. The ability of organic dyes to absorb light and promote transformations is known since the early stage of photochemistry, and they represent attractive alternatives to the established

• transition metal-based photocatalysts [14][15][16][17][18]. In addition to their ready availability and low cost, these molecules are often biocompatible, and they can be easily functionalized in order to modulate their spectroscopical and redox features. In the last years, several classes of organic dyes

Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches

• Rodrigo Costa e Silva,
• Luely Oliveira da Silva,
• Aloisio de Andrade Bartolomeu,
• Timothy John Brocksom and
• Kleber Thiago de Oliveira

Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83

• , 68502-100, Brazil 10.3762/bjoc.16.83 Abstract In this review we present relevant and recent applications of porphyrin derivatives as photocatalysts in organic synthesis, involving both single electron transfer (SET) and energy transfer (ET) mechanistic approaches. We demonstrate that these highly

• conjugated photosensitizers show increasing potential in photocatalysis since they combine both photo- and electrochemical properties which can substitute available metalloorganic photocatalysts. Batch and continuous-flow approaches are presented highlighting the relevance of enabling technologies for the

• overcome these issues, and leads to a drastic reduction of reaction time, lower photocatalyst loadings, minimization of the formation of byproducts [2] and uses visible light, which is considered a clean reagent [4]. Overall, visible light combined with organic photocatalysts such as porphyrinoids, make

A method to determine the correct photocatalyst concentration for photooxidation reactions conducted in continuous flow reactors

• Clemens R. Horn and
• Sylvain Gremetz

Beilstein J. Org. Chem. 2020, 16, 871–879, doi:10.3762/bjoc.16.78

• photocatalysts for the oxidation of citronellol (Scheme 1), using the conditions described by Lévesque and Seeberger [23]. The reaction conditions used for the experiments shown in Scheme 1 are detailed in Figure 2 below, and the best results are highlighted in grey. The conversions of the photooxidation

• (H) as a function of the liquid flow rate (top) and the residence time (bottom). Photocatalysts A–I screened for the oxidation of citronellol. Photooxidation of alpha-terpinene. Measured extinction coefficients and estimated ideal catalyst concentrations. Supporting Information Supporting

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• , having multiple advantages since ligand manipulation can lead to optimized photoredox properties. Unfortunately, the use of metals can pose some critical disadvantages in an organic process. Especially since the natural abundance of various noble metals that are used as photocatalysts is limited and

• since any pharmaceutically relevant compounds must not contain any metal contamination [5], the use of organic dyes is quite popular and can substitute the use of metal-based photocatalysts [6]. An alternative solution is the use of organic molecules as photocatalysts. There are already many reviews

• highlighting organocatalytically-mediated reactions [7][8][9][10] with potential in the field of photoorganocatalysis. The power of metal-based photocatalysts is indisputable and can be pinpointed through the ease that they can catalyze difficult photocatalytic reactions, such as the decarboxylation of

Photocatalytic deaminative benzylation and alkylation of tetrahydroisoquinolines with N-alkylpyrydinium salts

• David Schönbauer,
• Carlo Sambiagio,
• Timothy Noël and
• Michael Schnürch

Beilstein J. Org. Chem. 2020, 16, 809–817, doi:10.3762/bjoc.16.74

• screening the coupling between N-phenyl-THIQ (1) with N-benzyl-(2,4,6-triphenyl)pyridinium tetrafluoroborate (2, Table 1; the complete optimization table can be found in Supporting Information File 1). First, a screening of different photocatalysts was performed (Table 1, entries 1–4). The best results were

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• features to be used in the development of new photocatalysts. However, the study, development, and use of these complexes have been underexplored since the pioneering work of McMillin [14] and Sauvage [15], compared to the tremendous expansion of photocatalyzed reactions using Ru and Ir complexes. Indeed

• , copper-based photocatalysts are often considered less efficient due to a lower luminescence lifetime compared to Ir and Ru complexes [6]. Review In this review, we summarized the recent significant advances that were made in the use of copper-based photocatalysts for synthetically useful transformations

• molecule through a transfer of energy to a second one. Then, this second molecule is raised to the excited state and can then react [51][52]. During the course of the design of a library of copper photocatalysts through a combinatorial approach, Collins and co-workers reported the copper-photocatalyzed

Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations

• Rafia Siddiqui and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26

• neutrality; (iii) the use of household bulbs or LEDs as light sources under operationally simple reaction conditions; (iv) the high redox potential of photocatalysts that can manipulate the oxidation states of transition metal catalysts [54][55]. They have also found applications in novel solar cell

• functional materials [56], the reduction of carbon dioxide [57][58][59], etc. Additionally, inorganic chemists have utilized inorganic photocatalysts for functional components, viz, doping [60][61][62][63][64][65][66][67], encapsulated guests [68][69][70][71][72][73][74], molecular machines [75][76][77][78

• . This system is being used in C–C, C–N, C–O, C–S, and C–X bond-breaking and -forming processes [55]. Similarly, photoinduced direct hydrogen atom transfer (HAT) catalysis also plays a major role in the functionalization of intricate molecules. Photocatalysts that can undergo this process are uranyl

Dyes in modern organic chemistry

• Heiko Ihmels

Beilstein J. Org. Chem. 2019, 15, 2798–2800, doi:10.3762/bjoc.15.272

• versatile photocatalysts [17][18][19]. The investigation of dyes is also at the heart of physical organic chemistry. Specifically, the seminal studies to understand the relationship between structure and color are considered highlights in chemistry and contributed significantly to the development of

Excited state dynamics for visible-light sensitization of a photochromic benzil-subsituted phenoxyl-imidazolyl radical complex

• Yoichi Kobayashi,
• Yukie Mamiya,
• Katsuya Mutoh,
• Hikaru Sotome,
• Masafumi Koga,
• Hiroshi Miyasaka and
• Jiro Abe

Beilstein J. Org. Chem. 2019, 15, 2369–2379, doi:10.3762/bjoc.15.229

• photocatalysts because the lowest triplet excited (T1) state can be formed by light whose energy is smaller than that of the optically active transition [13][14][15][16]. However, photochromic reactions of some systems do not proceed via the T1 state. For example, it was reported that the photochromic reaction