An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

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

• electron-rich aryl disulfides as the photocatalyst and oxygen as the oxidant [16]. At room temperature, bis(4-methoxyphenyl) disulfide was employed as the metal-free photocatalyst under visible-light and 1 bar of O2 to realize the aerobic oxidative cleavage of the C=C bonds. Under these mild conditions

• of the aromatic S–S bond by visible light. In 2019, Meng and co-workers reported a visible light-mediated disulfide-catalyzed metal-free and base-free α-functionalization of 1,3-dicarbonyl compounds [17]. Under visible-light irradiation, the α-hydroxylation or α-hydroxymethylation of 1,3-dicarbonyl

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

• [46], Pb(OAc)4 [44][46][47][48][49][50][51], PbO2 [52], Mn(OAc)3 [46], KMnO4 [46], Ag2O [53], AgO [54], Horseradish peroxidase/H2O2 [55], metal-free oxidants PhI(OAc)2 [46], t-BuOOt-Bu [53] or quinones [56] under UV irradiation. Anodic oxidation was also reported [57]. The establishing of the self

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

• visible-light irradiation. The key aryl radical was trapped with heteroarenes, such as 11.2, to give the arylation products 11.3. Recently, similar methodologies for aryl radical generations have been developed exploiting flow techniques [74] and different organophotocatalysts, such as a metal-free

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

• reported a metal-free photoarylation of five-membered heteroarenes with aryldiazonium salts and meso-arylated porphyrin derivatives as photoredox catalyst [11]. Compounds such as furan, thiophene, and N-Boc-pyrrole derivatives were obtained by this methodology in 29–81% yields (Scheme 3). The key-step of

• this case, the authors observed the oxidative coupling between the primary amines and their respective imines to produce the secondary imines. Wang and co-workers reported the synthesis, characterization, and application of interesting metal-free heterogeneous photocatalysts, 2D porphyrin-COFs (Por-COF

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• yields were higher than in previously reported reactions, along with higher ees (Scheme 16, left). Although the synthesis of the ligand was somewhat tedious, the reaction proceeded in shorter reaction times [41]. Another approach, also shown below (Scheme 16, right), involves a metal-free background

KOt-Bu-promoted selective ring-opening N-alkylation of 2-oxazolines to access 2-aminoethyl acetates and N-substituted thiazolidinones

• Qiao Lin,
• Shiling Zhang and
• Bin Li

Beilstein J. Org. Chem. 2020, 16, 492–501, doi:10.3762/bjoc.16.44

• new and simple transition-metal-free selective ring-opening N-alkylation of 2-methyl-2-oxazoline or 2-(methylthio)-4,5-dihydrothiazole with benzyl halides and allyl halides under mild conditions. Various 2-aminoethyl acetates and N-substituted thiazolidinone derivatives were successfully isolated in

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

• shown to realize photoinitiated controlled/living radical polymerization of various monomers in metal free conditions. In the visible region, several dyes (fluorescein, eosin Y, erythrosin B) worked well to mediate ATRP in the presence of amines [72]. The reversibility of the electron transfer steps

• and deactivated by reaction with Cu(II) resulting in formation of dormant species and Cu(I). Altogether, these reactions must be seen as equilibrium coexisting together. Researchers also spent much time to develop photo-ATRP procedures working without any metal catalyst; that is the photoinduced metal

• -free ATRP strategy [132][133][134][135][136][137]. Latter reference provided a comprehensive overview demonstrating the function of phenothiazine derivatives, perylene, diaryl dihydrophenazines, anthracene or pyrene. In addition, type II photoinitiators including benzophenone, and thioxanthones were

p-Pyridinyl oxime carbamates: synthesis, DNA binding, DNA photocleaving activity and theoretical photodegradation studies

• Panagiotis S. Gritzapis,
• Panayiotis C. Varras,
• Nikolaos-Panagiotis Andreou,
• Katerina R. Katsani,
• Konstantinos Dafnopoulos,
• George Psomas,
• Zisis V. Peitsinis,
• Alexandros E. Koumbis and
• Konstantina C. Fylaktakidou

Beilstein J. Org. Chem. 2020, 16, 337–350, doi:10.3762/bjoc.16.33

• anticancer activity due to alteration of the structure and function of the genetic material. Amongst a plethora of such binders [1][2][3][4][5][6][7][8], various oxime derivatives were found to show affinity towards DNA [9][10][11][12], whereas others were found to cleave DNA as metal-free artificial

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

• cations, polyoxometallates, and benzophenones [9][80], but a major drawback is the limited availability of photocatalysts that can perform direct HAT. Therefore, there is a high demand for a direct-HAT catalyst that is accessible, metal-free, allows no side reactions, and can be activated by visible light

Construction of trisubstituted chromone skeletons carrying electron-withdrawing groups via PhIO-mediated dehydrogenation and its application to the synthesis of frutinone A

• Qiao Li,
• Chen Zhuang,
• Donghua Wang,
• Wei Zhang,
• Rongxuan Jia,
• Fengxia Sun,
• Yilin Zhang and
• Yunfei Du

Beilstein J. Org. Chem. 2019, 15, 2958–2965, doi:10.3762/bjoc.15.291

• , PhIO has never been utilized for the dehydrogenative oxidation reaction. In this letter, we report a facile PhIO-mediated dehydrogenation of chromanones, resulting in the efficient synthesis of biologically interesting chromone compounds under metal-free conditions. Results and Discussion We initially

• , we have developed an efficient metal-free approach for the synthesis of chromone derivatives via PhIO-mediated dehydrogenative oxidation of chromanones. Compared with the existing methods, the new reaction features mild conditions, high efficiency, and is metal-free. Moreover, the product 2l could be

Iodine-mediated hydration of alkynes on keto-functionalized scaffolds: mechanistic insight and the regiospecific hydration of internal alkynes

• Zachary Lee,
• Brandon R. Jones,
• Nyochembeng Nkengbeza,
• Michael Phillips,
• Kayla Valentine,
• Alexis Stewart,
• Brandon Sellers,
• Nicholas Shuber and
• Karelle S. Aiken

Beilstein J. Org. Chem. 2019, 15, 2747–2752, doi:10.3762/bjoc.15.265

• (II) [7], silver(I) [8], and gold(I)/(III) [9][10][11][12]. While less toxic than mercury, such catalysts are still environmental hazards and tend to be costlier [13][14]. The iodine-mediated hydration described herein is a viable solution to these issues [15][16]. This metal-free method produces

• innocuous, water-soluble byproducts, such as iodide and sulfate salts, and uses inexpensive molecular iodine to facilitate the hydration. Moreover, unlike other metal-free alkyne hydration procedures, heat and strong acids are not required [17][18][19][20]. The reaction proceeds under mild conditions at

Synthesis of aryl-substituted thieno[3,2-b]thiophene derivatives and their use for N,S-heterotetracene construction

• Nadezhda S. Demina,
• Nikita A. Kazin,
• Nikolay A. Rasputin,
• Roman A. Irgashev and
• Gennady L. Rusinov

Beilstein J. Org. Chem. 2019, 15, 2678–2683, doi:10.3762/bjoc.15.261

• effectively tune their physical characteristics and also reduce production costs since the routine synthesis of heteroacene structures involves cross-coupling reactions catalyzed by expensive transition metals [15]. Thus, in this paper, we would like to present an efficient metal-free synthesis of the aryl

Friedel–Crafts approach to the one-pot synthesis of methoxy-substituted thioxanthylium salts

• Kenta Tanaka,
• Yuta Tanaka,
• Mami Kishimoto,
• Yujiro Hoshino and
• Kiyoshi Honda

Beilstein J. Org. Chem. 2019, 15, 2105–2112, doi:10.3762/bjoc.15.208

• . Keywords: Friedel–Crafts reaction; metal-free conditions; one-pot synthesis; photoredox catalyst; thioxanthylium salt; Introduction Thioxanthylium salts are one of the important structural motifs found in biologically active compounds and photochemical materials [1][2][3][4][5][6][7][8]. Owing to these

Synthesis of benzo[d]imidazo[2,1-b]benzoselenoazoles: Cs₂CO₃-mediated cyclization of 1-(2-bromoaryl)benzimidazoles with selenium

• Mio Matsumura,
• Yuki Kitamura,
• Arisa Yamauchi,
• Yoshitaka Kanazawa,
• Yuki Murata,
• Tadashi Hyodo,
• Kentaro Yamaguchi and
• Shuji Yasuike

Beilstein J. Org. Chem. 2019, 15, 2029–2035, doi:10.3762/bjoc.15.199

• metal catalyst. We present in this paper the synthesis of benzo[d]imidazo[2,1-b]benzoselenoazoles under transition metal-free conditions by the Cs2CO3-mediated cyclization of 1-(2-bromoaryl)benzimidazoles with selenium. Results and Discussion We initially focused our attention on determining the optimal

A metal-free approach for the synthesis of amides/esters with pyridinium salts of phenacyl bromides via oxidative C–C bond cleavage

• Kesari Lakshmi Manasa,
• Yellaiah Tangella,
• Namballa Hari Krishna and
• Mallika Alvala

Beilstein J. Org. Chem. 2019, 15, 1864–1871, doi:10.3762/bjoc.15.182

• 10.3762/bjoc.15.182 Abstract An efficient, simple, and metal-free synthetic approach for the N- and O-benzoylation of various amines/benzyl alcohols with pyridinium salts of phenacyl bromides is demonstrated to generate the corresponding amides and esters. This protocol facilitates the oxidative cleavage

• restrict the substrate scope. Qandil et al. reported a transition metal-free approach for the formation of amides and esters from phenacyl bromides or chlorides [36]. Zhang et al. developed a milder and metal-free approach for the selective cleavage of C(CO)–C(α) bonds [37][38][39][40]. Kamal and co

• -workers also demonstrated a transition metal-free aerobic oxidative cleavage of C–C bonds of phenacyl azides employed in the construction of amides utilizing benzylamines [41]. Herein we wish to report a metal-free C(CO)–C(α) bond cleavage of pyridinium salts of phenacyl bromides for the facile synthesis

Metal-free mechanochemical oxidations in Ertalyte^® jars

• Andrea Porcheddu,
• Francesco Delogu,
• Lidia De Luca,
• Claudia Fattuoni and
• Evelina Colacino

Beilstein J. Org. Chem. 2019, 15, 1786–1794, doi:10.3762/bjoc.15.172

• against residual metals in manufactured goods and active ingredients stimulates the ongoing search for new metal-free solutions to the problem making this challenge even topical [26][27]. Based on the considerations mentioned above, we focused on an alternative strategy to activate the oxidation process

Functional panchromatic BODIPY dyes with near-infrared absorption: design, synthesis, characterization and use in dye-sensitized solar cells

• Quentin Huaulmé,
• Cyril Aumaitre,
• Outi Vilhelmiina Kontkanen,
• David Beljonne,
• Alexandra Sutter,
• Gilles Ulrich,
• Renaud Demadrille and
• Nicolas Leclerc

Beilstein J. Org. Chem. 2019, 15, 1758–1768, doi:10.3762/bjoc.15.169

• ] but these molecules reveal low absorption coefficients over the visible range. Furthermore, they contain a rare and a relatively high-cost element (Ru) and their plausible toxicity restrains their development at the industrial level. For these reasons, in the last decade, metal-free organic dyes based

A novel three-component reaction between isocyanides, alcohols or thiols and elemental sulfur: a mild, catalyst-free approach towards O-thiocarbamates and dithiocarbamates

• András György Németh,
• György Miklós Keserű and
• Péter Ábrányi-Balogh

Beilstein J. Org. Chem. 2019, 15, 1523–1533, doi:10.3762/bjoc.15.155

• functional group tolerance to halogen, olefin and nitrile groups among others. Moreover, this multicomponent reaction is suitable for a one-pot cascade annulation providing a thioxo dihydroquinazolinone derivative in a metal-free approach. Compared to other reported syntheses of thiocarbamates, this method

Robust perfluorophenylboronic acid-catalyzed stereoselective synthesis of 2,3-unsaturated O-, C-, N- and S-linked glycosides

• Madhu Babu Tatina,
• Xia Mengxin,
• Rao Peilin and
• Zaher M. A. Judeh

Beilstein J. Org. Chem. 2019, 15, 1275–1280, doi:10.3762/bjoc.15.125

• . The majority of the reported catalysts are metal-based, and in pharmaceutical manufacturing, traces of metals pose a major challenge for their removal to acceptable limits. Therefore, the discovery of efficient, metal-free and mild catalysts for the Ferrier rearrangement is still challenging and

Mechanochemical amorphization of chitin: impact of apparatus material on performance and contamination

• Thomas Di Nardo and
• Audrey Moores

Beilstein J. Org. Chem. 2019, 15, 1217–1225, doi:10.3762/bjoc.15.119

• stainless steel ones, since the latter caused the reactive mixture to adhere to the jars, which was not the case of the former. In another example, for the metal-free transfer hydrogenation of carbonyl compounds, PTFE was used instead of steel to eliminate the possibility of catalysis from the milling media

Mechanochemical synthesis of hyper-crosslinked polymers: influences on their pore structure and adsorption behaviour for organic vapors

• Sven Grätz,
• Sebastian Zink,
• Hanna Kraffczyk,
• Marcus Rose and
• Lars Borchardt

Beilstein J. Org. Chem. 2019, 15, 1154–1161, doi:10.3762/bjoc.15.112

• –Teller) surface areas of up to 2000 m2g−1 for fully amorphous materials [10]. Typically, chloromethyl or methoxy groups are used to crosslink aromatic building blocks by using stoichiometric or even excess amounts of FeCl3 as catalyst. Recently, also a metal-free Brønsted acid-catalyzed reaction using

Precious metal-free molecular machines for solar thermal energy storage

• Meglena I. Kandinska,
• Snejana M. Kitova,
• Vladimira S. Videva,
• Stanimir S. Stoyanov,
• Stanislava B. Yordanova,
• Stanislav B. Baluschev,
• Silvia E. Angelova and
• Aleksey A. Vasilev

Beilstein J. Org. Chem. 2019, 15, 1096–1106, doi:10.3762/bjoc.15.106

• -system [9] with a triplet–triplet annihilation photon energy upconversion system (TTA-UC) [10][11] an effective utilization of sub-bandgap photons is possible [12][13]. Nevertheless, the identification of a precious metal-free MOST system utilizing the visible part of the sun spectrum remains a

• spectra of the metal-free and Ba2+ complexed cis form of compound 4b are also presented in Figure 7. The oscillator strengths of the cis forms, calculated at the same computational level, are found to be significantly lower than those calculated for the respective trans forms (metal-free compound trans-4b

Multicomponent reactions (MCRs): a useful access to the synthesis of benzo-fused γ-lactams

• Edorta Martínez de Marigorta,
• Jesús M. de Los Santos,
• Ana M. Ochoa de Retana,
• Javier Vicario and
• Francisco Palacios

Beilstein J. Org. Chem. 2019, 15, 1065–1085, doi:10.3762/bjoc.15.104

• also been prepared in situ and used for a three-component transition-metal-free synthesis of phthalimides 79 induced by fluoride (Scheme 23) [102]. The reaction makes use of 2-(trimethylsilyl)aryl triflates 77, isocyanides 42 and CO2 (78), and takes place in acetonitrile as solvent and without the need

Catalytic asymmetric oxo-Diels–Alder reactions with chiral atropisomeric biphenyl diols

• Chi-Tung Yeung,
• Wesley Ting Kwok Chan,
• Wai-Sum Lo,
• Ga-Lai Law and
• Wing-Tak Wong

Beilstein J. Org. Chem. 2019, 15, 955–962, doi:10.3762/bjoc.15.92

• acid catalysts for over three decades [15][16][17][18][19][20][21][22][23][24][25][26]. Comparatively, interest in the utilization of metal-free organocatalytic oxo-DA reactions began to grow only after Rawal’s group reported a ground-breaking contribution in using a diol molecule, TADDOL, as a

Towards the preparation of synthetic outer membrane vesicle models with micromolar affinity to wheat germ agglutinin using a dialkyl thioglycoside

• Dimitri Fayolle,
• Nathalie Berthet,
• Bastien Doumeche,
• Olivier Renaudet,
• Peter Strazewski and
• Michele Fiore

Beilstein J. Org. Chem. 2019, 15, 937–946, doi:10.3762/bjoc.15.90

• addition of thiols to alkenes – known as thiol–ene coupling, TEC – a very efficient metal-free click reaction [18][19]. We prepared n-alkyl 1-thio-β--glycosides from unprotected sugar anomeric thiols, commercial n-alkenes and one synthetic lipophilic scaffold presenting two reactive alkenyl ends. Although