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

• photoprocesses [9][10][11]. Additionally, it is possible to realize tuning in terms of chemical properties by changing substituents, thus producing robust, soluble or heterogeneous, readily available and low-cost photocatalysts. The mechanisms of the photocatalytic activities of porphyrins are similar to other

• concerted) are still ongoing. The generally accepted mechanisms for these reactions are shown in Scheme 27, and propose a stepwise mechanism for ene and [2 + 2] cycloaddition, and a concerted mechanism for [4 + 2] cycloaddition [67]. In this part of the review, we decided to highlight the historically

• oxygen and their mechanisms. Adapted from [67]. First scaled up ascaridole preparation from α-terpinene. Antimalarial drug synthesis using an endoperoxidation approach. Photooxygenation of colchicine. Synthesis of (−)-pinocarvone from abundant (+)-α-pinene. Seeberger’s semi-synthesis of artemisinin

Cation-induced ring-opening and oxidation reaction of photoreluctant spirooxazine–quinolizinium conjugates

• Phil M. Pithan,
• Sören Steup and
• Heiko Ihmels

Beilstein J. Org. Chem. 2020, 16, 904–916, doi:10.3762/bjoc.16.82

• 0.93 (s, 3’-Me) that are again significantly shifted upfield in comparison to the ones of 4a. It has already been shown that spirooxazines may react in certain cases to oxazole derivatives. However, depending on the employed conditions, different mechanisms for the formation of these oxidation products

• (see discussion below). According to the concurrent assumption of the proposed mechanisms of the cation-induced ring opening of spirooxazines (see above), the metal cation initially coordinated to the phenolate oxygen of the merocyanine. Based on the possible transoid structures, it has already been

Synthesis of new asparagine-based glycopeptides for future scanning tunneling microscopy investigations

• Laura Sršan and
• Thomas Ziegler

Beilstein J. Org. Chem. 2020, 16, 888–894, doi:10.3762/bjoc.16.80

• mechanisms of the interaction of glycopeptides with the cell surface [16]. Our focus lay on the preparation of glycopeptide libraries containing ʟ-asparagine since many saccharides on the cell surface are N-glycosidically linked to this amino acid [8]. The most abundant sugars found in these asparagine

Preparation of 2-phospholene oxides by the isomerization of 3-phospholene oxides

• Péter Bagi,
• Réka Herbay,
• Nikolett Péczka,
• Zoltán Mucsi,
• István Timári and
• György Keglevich

Beilstein J. Org. Chem. 2020, 16, 818–832, doi:10.3762/bjoc.16.75

• -phospholene oxides in methanesulfonic acid, or via the formation of cyclic chlorophosphonium salts. Whereas mixtures of the 2- and 3-phospholene oxides formed, when the isomerization of 3-phospholene oxides was attempted under thermal conditions, or in the presence of a base. The mechanisms of the various

• . Moreover, we wish to interpret the different isomerization mechanisms by quantumchemical calculations. Results and Discussion Preparation of 1-substituted-3-methyl-2-phospholene oxides (4) via chlorophospholenium chlorides (2 and 3) The preparation of 2-phospholene oxides 4 was first attempted via the

• oxide, while the corresponding 2-phospholene oxides 4a or 7 are the preferred isomers for the unsubstituted or methyl-substituted phospholene oxide derivatives (Table 5, entries 1–3). According to the thermodynamic data without the consideration of the reaction mechanisms and transition states (Table 5

Combining enyne metathesis with long-established organic transformations: a powerful strategy for the sustainable synthesis of bioactive molecules

• Valerian Dragutan,
• Ileana Dragutan,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2020, 16, 738–755, doi:10.3762/bjoc.16.68

• review also shed light on the continuous improvement of protocols relying on this reaction, potentially leading to tailorable properties of earmarked therapeutic agents. Intramolecular (A) and intermolecular (B) enyne metathesis reactions. Ene–yne and yne–ene mechanisms for intramolecular enyne

Room-temperature Pd/Ag direct arylation enabled by a radical pathway

• Amy L. Mayhugh and
• Christine K. Luscombe

Beilstein J. Org. Chem. 2020, 16, 384–390, doi:10.3762/bjoc.16.36

• -temperature, Pd/Ag-catalyzed direct arylation systems are radical-mediated. This is in contrast to the commonly proposed two-electron mechanisms for direct arylation and appears to extend to other substrates such as benzo[b]thiophene and pentafluorobenzene. Keywords: direct arylation; indole; palladium

• proposed mechanisms for direct arylation (Scheme 2). Amongst these mechanisms, the most widely accepted is the concerted metalation–deprotonation (CMD) pathway [21]. Within the indole direct-arylation literature, however, there remains much discussion of an electrophilic metalation mechanism, with the

• room-temperature direct arylation reaction between indole and iodobenzene reported in ref. [12] and adapted in this work to study room-temperature DArP. Commonly discussed mechanisms for C2 selective direct arylation, none containing radical intermediates. Proposed mechanism for palladium radical

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

• . A variety of reaction mechanisms are initiated, which, aiming to the photocleaver, may lead to DNA damage. A requirement for nucleic acid’s and most protein’s “transparency” is irradiating at wavelengths longer than 310 nm [15]. “Transparency” means lack of damage due to irradiation itself and

Ultrasonic-assisted unusual four-component synthesis of 7-azolylamino-4,5,6,7-tetrahydroazolo[1,5-a]pyrimidines

• Yana I. Sakhno,
• Maryna V. Murlykina,
• Oleksandr I. Zbruyev,
• Anton V. Kozyryev,
• Svetlana V. Shishkina,
• Dmytro Sysoiev,
• Vladimir I. Musatov,
• Sergey M. Desenko and
• Valentyn A. Chebanov

Beilstein J. Org. Chem. 2020, 16, 281–289, doi:10.3762/bjoc.16.27

• described and discussed in publications [31][32]. We cannot exclude other mechanisms, for example, via arylidenepyruvic acids (esters) 11 formed by water elimination from appropriate aldols (pathway B). However, our attempts to synthesize compound 4 by direct reaction of unsaturated acid 8 and aminoazole 1a

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

• Figure 2. The most frequently used mechanisms of converting light energy into chemical energy using photoredox catalysts are: (i) photoredox catalysis; (ii) organometallic excitation; (iii) light-induced atom transfer, and (iv) energy transfer. Basically, a photoredox catalyst transforms light energy

The reaction of arylmethyl isocyanides and arylmethylamines with xanthate esters: a facile and unexpected synthesis of carbamothioates

• Narasimhamurthy Rajeev,
• Toreshettahally R. Swaroop,
• Ahmad I. Alrawashdeh,
• Shofiur Rahman,
• Abdullah Alodhayb,
• Seegehalli M. Anil,
• Kuppalli R. Kiran,
• Chandra,
• Paris E. Georghiou,
• Kanchugarakoppal S. Rangappa and
• Maralinganadoddi P. Sadashiva

Beilstein J. Org. Chem. 2020, 16, 159–167, doi:10.3762/bjoc.16.18

• hypothesis. Computational studies on the proposed reaction mechanism Several possible reaction mechanisms were considered to account for the unexpected products obtained. Ultimately, we employed quantum chemical calculations to shed light on the most probable reaction pathway for the observed products, as

• that could be supported by quantum chemical calculations. Of course, other alternative mechanisms that can be envisioned include one in which the thiolate anions, which were generated, could also either a) regenerate dimethylamide anions from the surrounding DMF solvent; and/or b) possibly add to the

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

• Katarzyna Włodarczyk,
• Piotr Borowski and
• Marek Stankevič

Beilstein J. Org. Chem. 2020, 16, 88–105, doi:10.3762/bjoc.16.11

• conditions clearly showed that distinct reaction mechanisms were responsible for the substrate’s transformation under Lewis and Brønsted acid catalysis, but both seemed to include the preliminary formation of alkenylphosphine sulfide. This was shown for the Brønsted acid-mediated reaction (Table 4) but

Understanding the role of active site residues in CotB2 catalysis using a cluster model

• Keren Raz,
• Ronja Driller,
• Thomas Brück,
• Bernhard Loll and
• Dan T. Major

Beilstein J. Org. Chem. 2020, 16, 50–59, doi:10.3762/bjoc.16.7

• ]. Theoretical quantum mechanical (QM) investigations on the chemistry of terpenes in the gas phase have provided a detailed understanding of the carbocation mechanisms underlying terpene synthase function [25][26][27]. Further, we have used multiscale modeling tools to study the effects of the enzyme

• highlight the importance of taking into account the active site residues while modeling terpene synthase mechanisms, as we have proposed previously [28][29][30][31][32][33][34][35][36][42]. We found that the energy surface in the active site model was significantly perturbed compared to the gas phase

Light-controllable dithienylethene-modified cyclic peptides: photoswitching the in vivo toxicity in zebrafish embryos

• Sergii Afonin,
• Oleg Babii,
• Aline Reuter,
• Volker Middel,
• Masanari Takamiya,
• Uwe Strähle,
• Igor V. Komarov and
• Anne S. Ulrich

Beilstein J. Org. Chem. 2020, 16, 39–49, doi:10.3762/bjoc.16.6

• plasma stability in vivo, limited understanding of their mechanisms of action, and high in vivo toxicity. The former two drawbacks are being adequately resolved [9] (e.g., by modifying the peptide backbone [10], macrocyclization [11], or by use of unnatural amino acids [12]), and mechanistic

• understanding of the relevant molecular mechanisms is gradually improving [13]. However, the safety consideration still poses a considerable challenge. Hence, the understanding and decreasing of the in vivo toxicity of peptides is of paramount importance for their development as drugs. In recent years

• infectious diseases caused by Gram-positive or -negative bacteria, or for anticancer applications. We hypothesized that the lack of correlation between cell types might not only reflect different mechanisms of killing (possibly even within any pair of isomers), but that it may also be due to unique

Synthesis of C-glycosyl phosphonate derivatives of 4-amino-4-deoxy-α-ʟ-arabinose

• Lukáš Kerner and
• Paul Kosma

Beilstein J. Org. Chem. 2020, 16, 9–14, doi:10.3762/bjoc.16.2

• mechanisms of pathogenic Gram-negative bacteria against antibiotics, such as polymyxin B and colistin [3]. The main effect of Ara4N incorporation into the lipid A part – and, less frequently, into the inner core region of LPS [4] – is thought to originate from blocking the electrostatic interaction of

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

• nonradical pathways. Based on previous reports [63][86] and our own experimental results, two plausible mechanisms for this dehydrogenation reaction are proposed (Scheme 4): In pathway a, substrate 1a is first tautomerized to its enol form A, which would be stabilized by an internal H-bond. It is highly

Chemical synthesis of tripeptide thioesters for the biotechnological incorporation into the myxobacterial secondary metabolite argyrin via mutasynthesis

• David C. B. Siebert,
• Roman Sommer,
• Domen Pogorevc,
• Michael Hoffmann,
• Silke C. Wenzel,
• Rolf Müller and
• Alexander Titz

Beilstein J. Org. Chem. 2019, 15, 2922–2929, doi:10.3762/bjoc.15.286

• ; mutasynthesis; NRPS; peptide synthesis; Introduction Resistance to antibiotics is currently a major threat to public health. Especially Gram-negative bacterial pathogens are of concern, due to their widespread development of resistance mechanisms. To address this general antimicrobial resistance problem, new

• , encoded by the gene fusA1) as their target [11][12]. The co-crystal structure of argyrin B (2) and P. aeruginosa EF-G1 provides structural information of the complex at atomic resolution as basis for further structure-based optimization [11]. Jones and colleagues analyzed possible resistance mechanisms to

Synthesis and optoelectronic properties of benzoquinone-based donor–acceptor compounds

• Daniel R. Sutherland,
• Nidhi Sharma,
• Georgina M. Rosair,
• Ifor D. W. Samuel,
• Ai-Lan Lee and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2019, 15, 2914–2921, doi:10.3762/bjoc.15.285

• chemistry; physical organic chemistry; spectroscopy; thermally activated delayed fluorescence; Introduction Substituted benzoquinones and derivatives [1] have generated great interest, in particular due to their redox-active nature and their importance in biological mechanisms [2]. Compounds bearing

• ) properties. In EL devices, such as organic light-emitting diodes (OLEDs), there are three main exciton-harvesting mechanisms for organic compounds that offer the potential to expand beyond the 25% internal quantum efficiency (IQE) offered by fluorophores: (1) phosphorescence, frequently mediated by a rare

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

• Eric J. N. Helfrich,
• Geng-Min Lin,
• Christopher A. Voigt and
• Jon Clardy

Beilstein J. Org. Chem. 2019, 15, 2889–2906, doi:10.3762/bjoc.15.283

• cyclization reactions. Textbook TCs are categorized into two classes and differ in their mechanisms of substrate activation as well as their protein folds [37][50][51][52]. Type I TCs trigger the formation of highly reactive allylic cations by heterolytic cleavage of the terminal pyrophosphate of farnesyl

• cyclization reactions have recently been extensively reviewed [53]. Many of these alternative cyclization routes have been shown to resemble classical type I and II cyclization mechanisms initiated by the formation of highly reactive short-lived carbocation intermediates (e.g., prenyltransferases [59][60

• decoration phase needs to be modified, as it is now known that enzyme families, traditionally regarded as tailoring enzymes, can potentially be involved in the cyclization reaction. The ever-increasing number of alternative terpene cyclization mechanisms suggests that nature has likely evolved additional

Emission and biosynthesis of volatile terpenoids from the plasmodial slime mold Physarum polycephalum

• Xinlu Chen,
• Tobias G. Köllner,
• Wangdan Xiong,
• Guo Wei and
• Feng Chen

Beilstein J. Org. Chem. 2019, 15, 2872–2880, doi:10.3762/bjoc.15.281

• similarities occurred between PpolyTPS1 and PpolyTPS4 (72%) and between PpolyTPS2 and PpolyTPS3 (64%). PpolyTPS1/4 and PpolyTPS2/3, however, showed only ≈30% sequence similarity to each other. Terpene synthases can be classified into class I and class II, based on the reaction mechanisms they catalyze. These

Progress in metathesis chemistry

• Karol Grela and
• Anna Kajetanowicz

Beilstein J. Org. Chem. 2019, 15, 2765–2766, doi:10.3762/bjoc.15.267

• observed a growing number of metathesis examples utilizing very low loading (at the single part-per-million level) of catalysts, which is crucial for the application of this reaction in the production of bulk chemicals. At the same time, much effort was invested in understanding the mechanisms of how new

A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• which have fast thermal Z–E conversion through mechanisms such as tautomerization. Furthermore, the study of Venkataramani and co-workers did not particularly focus on substitution patterns known to give high performance in azobenzene switches. We therefore considered whether specifically combining the

Unexpected one-pot formation of the 1H-6a,8a-epiminotricyclopenta[a,c,e][8]annulene system from cyclopentanone, ammonia and dimethyl fumarate. Synthesis of highly strained polycyclic nitroxide and EPR study

• Sergey A. Dobrynin,
• Igor A. Kirilyuk,
• Yuri V. Gatilov,
• Andrey A. Kuzhelev,
• Olesya A. Krumkacheva,
• Matvey V. Fedin,
• Michael K. Bowman and
• Elena G. Bagryanskaya

Beilstein J. Org. Chem. 2019, 15, 2664–2670, doi:10.3762/bjoc.15.259

• hindered nitroxide, we investigated its electron spin relaxation properties in water/glycerol solution which is the solvent of choice for biomolecular distance measurements by PELDOR/DEER. If the rotation of the radical is prevented, the primary relaxation mechanisms are (i) modulation of the 14N hyperfine

Acid-catalyzed rearrangements in arenes: interconversions in the quaterphenyl series

• Sarah L. Skraba-Joiner,
• Carter J. Holt and
• Richard P. Johnson

Beilstein J. Org. Chem. 2019, 15, 2655–2663, doi:10.3762/bjoc.15.258

• displays such a complex and fascinating collection of molecular rearrangements. Building on a long history, new synthetic applications [1][2] and explanations of carbocation reaction mechanisms [3][4][5][6] continue to be discovered. Chemistry in superacid solutions has played a major role in this field [7

• favoring the 2,2'-isomer 9 (97%) at equilibrium [26]. Aryl shifts occur readily in naphthalene, with beta-substitution favored at equilibrium. Skeletal rearrangements of fused arene rings are also possible and can proceed through several mechanisms. The first example was reported by Dansi and Salvioni in

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• a prevalent catalyst in a huge number of organic transformations. Similar to palladium complexes, copper complexes generally exist in four oxidation states, Cu(0), Cu(I), Cu(II), and Cu(III) and various fluorination reactions could be developed by different catalytic mechanisms. Fluorination of

Aggregation-induced emission effect on turn-off fluorescent switching of a photochromic diarylethene

• Luna Kono,
• Yuma Nakagawa,
• Ayako Fujimoto,
• Ryo Nishimura,
• Yohei Hattori,
• Toshiki Mutai,
• Nobuhiro Yasuda,
• Kenichi Koizumi,
• Satoshi Yokojima,
• Shinichiro Nakamura and
• Kingo Uchida

Beilstein J. Org. Chem. 2019, 15, 2204–2212, doi:10.3762/bjoc.15.217

• is one of the examples which express the mechanisms of aggregation-induced emission (AIE). This compound emits orange fluorescence with a large Stokes shift derived from ESIPT in aprotic solvents such as THF or hexane, while it exhibits only a photochromic reaction in protic solvents such as methanol