Light-responsive rotaxane-based materials: inducing motion in the solid state

• Adrian Saura-Sanmartin

Beilstein J. Org. Chem. 2023, 19, 873–880, doi:10.3762/bjoc.19.64

• different flexibility. The crown ether derivative acts as a chassis in order to fix the thread. A ferrocenyl group attached at one of the ends of the linear component serves as a photosensitizer allowing the absorption of visible light. The different substitution induced different types of deformations

• motifs in rotaxane-based polymers has also provided interesting properties which can be employed in some specific implementations. α-Cyclodextin-based polyrotaxanes 2 having trithiocarbonate stopper groups with an adjacent phenyl group were employed for the construction of visible light-degradable

• (Figure 2b). Interestingly, the viscosity of the gels was progressively reduced due to the decrease of the physical entanglement of the polymeric chains via photodegradation. Thus, the viscoelasticity of the rotaxane-based gels could be fine-tuned by modifying the irradiation time. This visible-light

Photocatalytic sequential C–H functionalization expediting acetoxymalonylation of imidazo heterocycles

• Deepak Singh,
• Shyamal Pramanik and
• Soumitra Maity

Beilstein J. Org. Chem. 2023, 19, 666–673, doi:10.3762/bjoc.19.48

• chemodivergent formation of C-3 ethoxycarbonylmethylated and hydroxyalkylated IPs under visible light using water or alcohol as the source of the oxygenated group under degassed conditions [22]. However, all these photochemical methods require the usage of a substantial amount of base, the preactivation with a

Direct C2–H alkylation of indoles driven by the photochemical activity of halogen-bonded complexes

• Martina Mamone,
• Giuseppe Gentile,
• Jacopo Dosso,
• Maurizio Prato and
• Giacomo Filippini

Beilstein J. Org. Chem. 2023, 19, 575–581, doi:10.3762/bjoc.19.42

• substrates [13][14][15][16][17][18]. In this approach, an electron acceptor substrate (“A”) and a donor molecule (“D”) interact to form a new aggregate defined as EDA complex (Figure 1a). Although the two molecular entities might not directly absorb visible light, the newly formed complex usually presents a

• ambient temperature and under visible-light irradiation. Interestingly, this method employs 1,4-diazabicyclo[2.2.2]octane (DABCO) as sacrificial donor in the EDA complex formation with 2. To test the feasibility of our design plan, we focused on the reaction between 3-methylindole (1a, 2 equiv) and α

Transition-metal-catalyzed C–H bond activation as a sustainable strategy for the synthesis of fluorinated molecules: an overview

• Louis Monsigny,
• Floriane Doche and
• Tatiana Besset

Beilstein J. Org. Chem. 2023, 19, 448–473, doi:10.3762/bjoc.19.35

• Co catalysis [165][166][167]. In 2022, Volla and co-workers reported the ortho-2,2,2-trifluoroethoxylation of benzamide using an N,O-bidentate directing group by merging Co- and visible light organophotocatalysis [168]. Palladium catalysis: In 2017, Ji, Li and co-workers reported a thorough study on

NaI/PPh₃-catalyzed visible-light-mediated decarboxylative radical cascade cyclization of N-arylacrylamides for the efficient synthesis of quaternary oxindoles

• Dan Liu,
• Yue Zhao and
• Frederic W. Patureau

Beilstein J. Org. Chem. 2023, 19, 57–65, doi:10.3762/bjoc.19.5

• is mediated by visible light irradiation. A wide range of substrates bearing different substituents and derived from ubiquitous carboxylic acids, including α-amino acids, were synthesized and examined under this very mild, efficient, and cost effective transition-metal-free synthetic method. These

• reported a Ru(bpy)3Cl2-catalyzed synthesis of N-Boc proline oxindole derivatives under visible-light assistance [47]. Therein, N-hydroxyphthalimide (NPhth) esters were utilized as alkyl radical precursors, which can be readily prepared from highly available carboxylic acids. In 2015, Cheng and co-workers

• disclosed a visible light-mediated radical tandem cyclization of N-arylacrylamides with N-(acyloxy)phthalimides to access 3,3-dialkylated oxindoles in the presence of [Ru(bpy)3Cl2]·6H2O [46]. However, these seminal methods remain limited by the need of noble-metal-based photocatalysts, excess additives and

Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field

• Elena R. Lopat’eva,
• Igor B. Krylov,
• Dmitry A. Lapshin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2022, 18, 1672–1695, doi:10.3762/bjoc.18.179

• photoredox-catalyst or electrochemically on an anode. An example of the photochemical aerobic benzylic CH-oxidation employing a heterogeneous photoredox catalyst, nanosized TiO2, was demonstrated by our group [85] (Scheme 9). Mixing of NHPI and TiO2 leads to the emergence of visible light absorbance

• under visible light irradiation. The advantages of this mixed hetero-/homogeneous catalytic system include the easy separation of the products from NHPI and TiO2, recyclability, selectivity control by TiO2/NHPI ratio, and high efficiency at low TiO2 loading due to the radical chain nature of the

• enantioselective hydroxylation of benzylic positions was achieved using a chiral aryl iodide mediator [148] (Scheme 34). At the first stage, under the action of m-CPBA and sodium bromide an active form of the catalyst ArI3-Br is formed, in which the iodine–bromine bond is cleaved homolytically under visible light

Derivatives of benzo-1,4-thiazine-3-carboxylic acid and the corresponding amino acid conjugates

• Péter Kisszékelyi,
• Tibor Peňaška,
• Klára Stankovianska,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2022, 18, 1195–1202, doi:10.3762/bjoc.18.124

• significantly accelerated by ultrasonic irradiation [16]. Cyclocondensation of 1,3-dicarbonyl compounds with substituted diaryl disulfides in water in the presence of β-cyclodextrin gave 2,3-disubstituted benzo-1,4-thiazines in 70–91% yield in 50 min [17]. A highly efficient visible-light-mediated one-pot

Heterogeneous metallaphotoredox catalysis in a continuous-flow packed-bed reactor

• Wei-Hsin Hsu,
• Susanne Reischauer,
• Peter H. Seeberger,
• Bartholomäus Pieber and
• Dario Cambié

Beilstein J. Org. Chem. 2022, 18, 1123–1130, doi:10.3762/bjoc.18.115

• ; heterogeneous catalysis; metallaphotoredox catalysis; packed bed; photochemistry; Introduction The amount and impact of visible-light-mediated protocols in organic synthesis have increased dramatically since the late 2000s [1]. The main driving force of this phenomenon is the novel reactivity afforded by

• visible-light photocatalysts that enable new reaction pathways that were previously difficult or impossible to realize [2]. Technical advancements, such as the rise of light-emitting diodes (LEDs) and new reactor technologies were similarly important incentives to popularize light-mediated organic

Electrochemical formal homocoupling of sec-alcohols

• Kosuke Yamamoto,
• Kazuhisa Arita,
• Masashi Shiota,
• Masami Kuriyama and
• Osamu Onomura

Beilstein J. Org. Chem. 2022, 18, 1062–1069, doi:10.3762/bjoc.18.108

• catalytic amount of transition-metal reductants have been developed, but stoichiometric silicon electrophiles and co-reductants such as Zn were commonly required to complete the catalytic cycle [14]. More recently, visible light-mediated pinacol coupling reactions have been disclosed by several groups [15

Continuous flow synthesis of azobenzenes via Baeyer–Mills reaction

• Jan H. Griwatz,
• Anne Kunz and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2022, 18, 781–787, doi:10.3762/bjoc.18.78

• only the geometry is altered from the planar (E)-AB to its twisted (Z)-AB form, but also its properties change (e.g., dipole moment and polarity) [13][14]. Furthermore, the (Z)-AB can be reversibly switched back by visible light or thermally [15]. To synthesize ABs a variety of reactions can be chosen

Structural basis for endoperoxide-forming oxygenases

• Takahiro Mori and
• Ikuro Abe

Beilstein J. Org. Chem. 2022, 18, 707–721, doi:10.3762/bjoc.18.71

• photosensitizers or visible light, non-enzymatically reacts with the biosynthetic intermediates to produce endoperoxide structures [16][22][23]. However, over the past three decades, only a few endoperoxide-forming enzymes have been identified, including the cyclooxygenases in the biosynthesis of prostaglandins

Heteroleptic metallosupramolecular aggregates/complexation for supramolecular catalysis

• Prodip Howlader and
• Michael Schmittel

Beilstein J. Org. Chem. 2022, 18, 597–630, doi:10.3762/bjoc.18.62

• + 26), respectively, were successfully employed as visible-light photocatalysts for a cross-coupling cyclization of N,N-dimethylaniline (27) and N-alkyl/aryl maleimides 28 (Figure 6). Notably, the systems showed much higher catalytic activity compared to similar reactions with the dye or cages alone

Tetraphenylethylene-embedded pillar[5]arene-based orthogonal self-assembly for efficient photocatalysis in water

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

Beilstein J. Org. Chem. 2022, 18, 429–437, doi:10.3762/bjoc.18.45

• chromophoric dye molecules can be utilized in photoredox reactions under the irradiation of light with suitable wavelength [6]. However, in the case of the m-TPEWP5G-EsY nanosystem, which contains conjugated molecules and displays harvesting antenna effects from ultraviolet to visible light wavelengths, solar

• FRET process, whilst the m-TPEWP5G-EsY nanorod assembly could act as a nanoreactor providing a suitable environment for the photochemical catalytic reaction in aqueous solution under visible light irradiation. In the presence of 0.5 mol % m-TPEWP5G-EY in aqueous solution, 2-bromo-1-phenylethanone (1a

Recent developments and trends in the iron- and cobalt-catalyzed Sonogashira reactions

• Surendran Amrutha,
• Sankaran Radhika and
• Gopinathan Anilkumar

Beilstein J. Org. Chem. 2022, 18, 262–285, doi:10.3762/bjoc.18.31

• bonds. This protocol involves the visible light-assisted Sonogashira coupling of aryl bromides and terminal alkynes in the presence of the Co(C9H9NO2)3 complex as the catalyst (Scheme 34) [45]. This novel catalytic system provided 23 alkyne products in a substrate scope study using ethylene glycol as

• additive and K2CO3 as base in DMF under visible light irradiation. The reaction of Co(OAc)2·4H2O with 2-(hydroxyimino)-1-phenylpropan-1-one in EtOH resulted in the formation of the Co catalyst. The coupling strategy exhibited only poor activity by the use of pure Co salts and the reaction was promoted by

• -substituted bromobenzenes with phenylacetylene in the presence of Co(C9H9NO2)3. Possible mechanism for the visible light-assisted cobalt complex-catalyzed Sonogashira coupling. (Reproduced with permission from ChemCatChem. 2018, 10, 758–762.) Sonogashira cross-coupling of aryl halides and phenylacetylene

Recent advances and perspectives in ruthenium-catalyzed cyanation reactions

• Thaipparambil Aneeja,
• Cheriya Mukkolakkal Abdulla Afsina,
• Padinjare Veetil Saranya and
• Gopinathan Anilkumar

Beilstein J. Org. Chem. 2022, 18, 37–52, doi:10.3762/bjoc.18.4

• conditions, readily available reagents, lower catalyst loading, and the use of cost effective atmospheric oxygen and visible light are the most attractive characteristics of this reaction. Xu et al. in 2016 discussed the deboronative cyanation of alkyltrifluoroborates using [Ru(bpy)3](PF6)2 as the photoredox

• catalyst [41]. This method provides an efficient pathway to 1°, 2°, and 3° alkyl nitriles using p‐toluenesulfonyl cyanide (TsCN) in CH2Cl2/H2O under visible-light irradiation (Scheme 17). 1‐Acetoxy‐1,2‐benziodoxol‐3‐(1H)‐one (BI‐OAc) was chosen as the oxidant and TFA as the additive in this method. A lower

• -up, high reproducibility and yields, lower catalyst loading, high product purity, and excellent selectivity. A visible-light-promoted Strecker-type functionalization of N-aryl-substituted tetrahydroisoquinolines under flow conditions was reported (Scheme 22) [45]. The cyanating agent utilized was

Iron-catalyzed domino coupling reactions of π-systems

• Austin Pounder and
• William Tam

Beilstein J. Org. Chem. 2021, 17, 2848–2893, doi:10.3762/bjoc.17.196

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

• -planar geometry, thereby resulting in a shorter excited state lifetime compared with ruthenium and iridium-based photocatalysts and thus limiting the application of CuI complexes to visible-light-mediated organic syntheses [22][31]. Homoleptic CuI bisphenanthroline complexes were designed with

• homolysis to produce CuI species and radical intermediates. These intermediates can initiate productive organic transformations [39]. 2.1 Visible-light-mediated Cu(I) catalytic cycle Upon the absorption of a photon (Scheme 4), CuILn forms a singlet MLCT state, which subsequently yields the excited triplet

• , in path b (a rebound cycle), CuI* is trapped after a SET by the radical intermediate to generate a CuIII species, which undergoes ligand exchange with the nucleophile and reductive elimination to produce the target product and the regenerated CuI catalyst [37][38][40]. 2.2 Visible-light-mediated Cu(I

Synthesis of phenanthridines via a novel photochemically-mediated cyclization and application to the synthesis of triphaeridine

• Songeziwe Ntsimango,
• Kennedy J. Ngwira,
• Moira L. Bode and
• Charles B. de Koning

Beilstein J. Org. Chem. 2021, 17, 2340–2347, doi:10.3762/bjoc.17.152

• visible light photoredox-catalyzed cyclizations also afforded phenanthridines (Figure 2, reaction 3) [11]. Inspired by the Rodrıguez and Walton approach, we sought to synthesize the nitrogen analogue of an angucycline known as phenanthroviridone 6, [12] from oxime 7 (Scheme 1). Based on the results

A visible-light-induced, metal-free bis-arylation of 2,5-dichlorobenzoquinone

• Pieterjan Winant and
• Wim Dehaen

Beilstein J. Org. Chem. 2021, 17, 2315–2320, doi:10.3762/bjoc.17.149

• salts are generated in situ and converted to radicals through irradiation with visible light. Reaction products precipitate from the solvent, eliminating the need for purification and thus providing a novel green method for the synthesis of versatile bis-electrophiles. Keywords: benzoquinone; diazonium

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

• developments, which enables a diverse range of previously inaccessible organic transformations in milder reaction conditions [31][32][33][34][35][36][37][38][39][40]. Here, by absorbing visible light, a photocatalyst can function as a single-electron redox mediator through an oxidative or reductive quenching

• were found to be suitable to achieve the transformation in satisfactory yields under visible light irradiation (Scheme 2). The authors hypothesized that the key α-nitrogen carbon-centered radical 5 could be generated via a photoredox-driven N-phenyl oxidation and α-C–H deprotonation sequence from

Towards new NIR dyes for free radical photopolymerization processes

• Haifaa Mokbel,
• Guillaume Noirbent,
• Didier Gigmes,
• Frédéric Dumur and
• Jacques Lalevée

Beilstein J. Org. Chem. 2021, 17, 2067–2076, doi:10.3762/bjoc.17.133

• conversions. To prevent the use of harmful UV light, different longer-wavelength photoinitiating systems (PISs) were proposed, e.g., blue light in dental materials [1][2]. Many PISs were developed for visible light, but much less studies are focused on the polymerization using near-Infrared (NIR) sources [3

• obtained with low energy and a moderate device cost contrary to thermal solutions; ii) mild irradiation conditions: safer and cheaper systems; and iii) the curing of thick and/or filled systems that cannot be addressed with UV or even visible-light-sensitive systems. Thus, the NIR curing of thick and

Recent advances in the syntheses of anthracene derivatives

• Giovanni S. Baviera and
• Paulo M. Donate

Beilstein J. Org. Chem. 2021, 17, 2028–2050, doi:10.3762/bjoc.17.131

• employed palladium(II) acetate and visible light under O2 in the reactions between ethyl acrylate (192) and substituted diaryl carboxylic acids 193, to produce anthraquinones 194 in low to moderate yields (30–68%). In a direct comparison with the methodology proposed by Hong for the synthesis of

• anthracenes, previously shown in Scheme 7 [41], the key to obtaining anthraquinones was the photooxidation induced by visible light, which afforded the substituted anthraquinones 194. In this case, the effect of the aromatic ring substituents also affected the yield of the anthraquinones, as can be seen from

• multicomponent reactions employing 2-hydroxy-1,4-naphthoquinone (186), β-naphthol (181), and aromatic aldehydes. Synthesis of substituted anthraquinones catalyzed by an AlCl3/MeSO3H system. Palladium(II)-catalyzed/visible light-mediated synthesis of anthraquinones. [4 + 2] Anionic annulation reaction for the

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

• has been selectively feasible without activating a C(sp2)–H bond in the arene moiety. Verma and co-workers [91] have reported the use of VO(acac)2 immobilized over graphitic carbon nitride (VO@gC3N4) under visible light irradiation to perform a photocatalytic C–H activation of arene methides and

• are crucial. In 2018, Ackermann and co-workers described a novel room temperature C–H arylation by using a continuous visible light photo-flow technique, allied with a manganese photocatalyst CpMn(CO)3 [142]. The new flow protocol enabled the synthesis of several arene- and heterocyclic-based

Sustainable manganese catalysis for late-stage C–H functionalization of bioactive structural motifs

• Jongwoo Son

Beilstein J. Org. Chem. 2021, 17, 1733–1751, doi:10.3762/bjoc.17.122

• , azidated N-protected memantine 13a was successfully generated by employing electricity and visible-light irradiation in the presence of a Mn catalyst. High regioselectivity was observed at tertiary or benzylic positions (see 13a–c). For commercially available drug derivatives, methyl esters of ibuprofen

• excluded. This late-stage process by Mn catalysis, electrochemistry, and visible-light catalysis exhibits high value as a sustainable tool to investigate problematic synthetic transformations. Recently, the Ackermann group disclosed a convenient manganese-catalyzed late-stage C–H azidation of bioactive

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

• ; aldehydes; cerium; oxidation; ketones; visible light; Introduction The selective oxidation of alcohols to carbonyl compounds [1][2] is an important process for producing a wide range of value-added fine chemicals [3][4][5][6]. In the traditional oxidation process stoichiometric amounts of oxidants such as

• acting as the terminal oxidant [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Most aerobic oxidation reactions utilize either metal complexes and nanoparticles or persistent radical reagents as catalysts [21]. In the past ten years, visible light-induced

• generating oxygen-centered radicals, that lead to carbon-centered radicals through intra/intermolecular hydrogen atom transfer (HAT) processes, radical decarboxylative or radical deformylation [57][58][59]. In continuation of our research interest on visible-light-driven cerium photocatalysis [59][65], we