Catalytic aza-Nazarov cyclization reactions to access α-methylene-γ-lactam heterocycles

• Bilge Banu Yagci,
• Selin Ezgi Donmez,
• Onur Şahin and
• Yunus Emre Türkmen

Beilstein J. Org. Chem. 2023, 19, 66–77, doi:10.3762/bjoc.19.6

• isolated in 54% yield (Table 1, entry 8). The exchange of chloride with the non-coordinating BF4− anion, driven by the precipitation of NaCl, is proposed to be responsible for this positive result. Next, we turned our attention to the use of hydrogen-bond donors as anion-binding catalysts [57][58]. To this

• (Table 1, entry 11). With this promising result in hand, we next examined the use of squaramides, which were shown to be highly effective hydrogen-bonding catalysts in a broad range of transformations [61][62][63][64]. When achiral squaramide derivatives 11 [65] and 12 [66] were tested in stoichiometric

• amount to promote the aza-Nazarov reactions investigated in this study, the results discussed above showcase the potential of strong hydrogen-bond donors as effective anion binding catalysts for this transformation. Finally, it should be noted that all aza-Nazarov products that are presented in Table 1

Modern flow chemistry – prospect and advantage

• Philipp Heretsch

Beilstein J. Org. Chem. 2023, 19, 33–35, doi:10.3762/bjoc.19.3

• ]. Analogously, significantly increased photon transfer in flow reactors has been exploited. Where the molar attenuation coefficient is high, such as in many important photoredox catalysts, most of the irradiation is already absorbed within a thin layer of a few millimeters. Thus, in batch reactors the vast

Inline purification in continuous flow synthesis – opportunities and challenges

• Jorge García-Lacuna and
• Marcus Baumann

Beilstein J. Org. Chem. 2022, 18, 1720–1740, doi:10.3762/bjoc.18.182

• -based inline extractions as the final purification step are rare, many applications exploit this approach as part of telescoped flow syntheses. This clearly shows the value of this approach for purifying reaction intermediates to remove spent reagents and unreacted reactants or remaining catalysts prior

• only. This is facilitated when using heterogeneous catalysts or immobilized enzymes that are retained in cartridge reactors. For instance, Paradisi and co-workers reported an N-acetylation approach to produce melatonin analogs, where the pure product is obtained in the organic phase after evaporation

• in industrial applications which may indicate an initial barrier of transferring such academic solutions from one group to another. Heterogeneous scavenging The versatility of flow technology allows researchers to use different immobilized reagents/catalysts in cartridges to perform reactions in a

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

• redox-neutral asymmetric organocatalysis, whereas organocatalysis by redox-active molecules stays in the shadows. For example, redox-active organic molecules are almost not mentioned in some recent overviews of compound types used in organocatalysis [3][12][13], except for photoredox catalysts [12][13

• ]. The well-known and convenient classification of organocatalysts into Lewis bases, Lewis acids, Brønsted bases, and Brønsted acids [1] also leaves the redox-organocatalysts behind. Moreover, in numerous research papers employing redox-active molecules as catalysts the developed processes are not

• ][29] and specialized on the specific types of organophotoredox catalysts, such as quinone derivatives [30][31], carbon nitrides [32][33], eosin [34][35][36], 4CzIPN [37][38], Bodipy derivatives [39], methylene blue [40], pyrylium salts [41], and perylene diimides [42]. Photochemical processes

Rhodium-catalyzed intramolecular reductive aldol-type cyclization: Application for the synthesis of a chiral necic acid lactone

• Motoyuki Isoda,
• Kazuyuki Sato,
• Kenta Kameda,
• Kana Wakabayashi,
• Ryota Sato,
• Hideki Minami,
• Yukiko Karuo,
• Atsushi Tarui,
• Kentaro Kawai and
• Masaaki Omote

Beilstein J. Org. Chem. 2022, 18, 1642–1648, doi:10.3762/bjoc.18.176

• . Therefore, various types of intramolecular aldol-type reactions have been developed and widely applied to the total synthesis of diverse natural products [9][10][11][12][13][14][15][16][17][18]. The reductive aldol-type reaction is another important variation that has been reported using metal catalysts

• development of a rhodium-catalyzed intramolecular reductive cyclization, we found that using [RhCl(cod)]2 improved the diastereomeric ratio of the products compared with other Rh catalysts. It seems that using [RhCl(cod)]2 leads to milder reaction conditions that lead to highly improved diastereomeric ratios

Formal total synthesis of macarpine via a Au(I)-catalyzed 6-endo-dig cycloisomerization strategy

• Jiayue Fu,
• Bingbing Li,
• Zefang Zhou,
• Maosheng Cheng,
• Lu Yang and
• Yongxiang Liu

Beilstein J. Org. Chem. 2022, 18, 1589–1595, doi:10.3762/bjoc.18.169

• ) itself failed to catalyze the cycloisomerization (Table 1, entry 1). Evaluation of a number of silver salts illustrated that silver hexafluoroantimonate (AgSbF6) was the optimal additive to activate the gold catalyst (Table 1, entries 2, 3, and 7). Screening of the other ligands of Au(I) catalysts

An alternative C–P cross-coupling route for the synthesis of novel V-shaped aryldiphosphonic acids

• Stephen J. I. Shearan,
• Enrico Andreoli and
• Marco Taddei

Beilstein J. Org. Chem. 2022, 18, 1518–1523, doi:10.3762/bjoc.18.160

• aryl halides and trialkyl phosphites [23]. Some of the most studied C–P coupling reactions involving aryl substrates are those employing catalysts, which are required in order to lower the energy barrier of the reaction and overcome the poor reactivity between aryl halides and trialkyl phosphites [24

• ][25][26]. These catalytic cross-coupling reactions tend to follow similar pathways to the Michaelis–Arbuzov reaction, with the inclusion of a catalytic intermediate step. A number of suitable catalysts have been identified, ranging from nickel(II) bromide and nickel(II) chloride, to palladium(II

• ) acetate and palladium(II) chloride [23][27][28]. Reactions involving these catalysts are most often carried out at high temperatures, usually in excess of 160 °C, and involve slow dropwise addition of the trialkyl phosphite to the substrate [23]. In the search for milder reaction conditions, a new

Cyclometalated iridium complexes-catalyzed acceptorless dehydrogenative coupling reaction: construction of quinoline derivatives and evaluation of their antimicrobial activities

• Hongling Shui,
• Yuhong Zhong,
• Renshi Luo,
• Zhanyi Zhang,
• Jiuzhong Huang,
• Ping Yang and
• Nianhua Luo

Beilstein J. Org. Chem. 2022, 18, 1507–1517, doi:10.3762/bjoc.18.159

• reactions have the advantages of high atom economy, simple operation, clean and green, and have become a research hotspot [31][32][33][34][35]. Cyclometalated iridium complexes with good catalytic efficiency and selectivity are very effective catalysts in ADC reactions. Moreover, these catalysts are easy to

• ][42], we found that cyclometalated iridium catalysts can effectively catalyze the dehydrogenation of alcohols to produce carbonyl compounds and hydrogen gas. Therefore, we used cyclometalated iridium complex (TC-6) to catalyze the ADC reaction of o-aminobenzyl alcohols 1 and aryl/heteroaryl/alkyl

• accompanied by 27% yield of 1,2-dihydroquinoline 4aa (Table 1, entry 1). Then, several other cyclometalated iridium complexes were studied. The catalysts TC-2 and TC-4 containing electron-donating ligands provided quinoline 3aa in higher chemoselectivity and yield (Table 1, entries 2 and 4). On the contrary

Molecular and macromolecular electrochemistry: synthesis, mechanism, and redox properties

• Shinsuke Inagi and
• Mahito Atobe

Beilstein J. Org. Chem. 2022, 18, 1505–1506, doi:10.3762/bjoc.18.158

• , polymer electrolyte membrane electrolysis technology, and new methods coupled with photoredox catalysts or transition metal catalysis, resulting in remarkable progress in organic electrosynthetic processes. Theoretical calculations have also led to a better understanding of the electron transfer behavior

Microelectrode arrays, electrosynthesis, and the optimization of signaling on an inert, stable surface

• Kendra Drayton-White,
• Siyue Liu,
• Yu-Chia Chang,
• Sakashi Uppal and
• Kevin D. Moeller

Beilstein J. Org. Chem. 2022, 18, 1488–1498, doi:10.3762/bjoc.18.156

• detection methods in the subsequent binding studies. The polymer network is not permeable to molecules tethered to its surface or proteins in solution. The synthetic problem was solved by using the electrodes in an array to generate chemical reagents and catalysts and then confining those reagents and

• catalysts (and the reactions they mediate) to the surface of the electrodes for their generation [10][11]. For the subsequent signaling experiments, the impedance-based approach outlined above has proven effective with polymer-coated electrodes (Figure 3). As described, this method works by inserting a

Design, synthesis, and evaluation of chiral thiophosphorus acids as organocatalysts

• Karen R. Winters and
• Jean-Luc Montchamp

Beilstein J. Org. Chem. 2022, 18, 1471–1478, doi:10.3762/bjoc.18.154

• value of the CPAs described in the literature, several disadvantages can be identified [18]. As mentioned above, C2-symmetry is required for the catalysts to provide a chiral pocket around the phosphorus. As a result, the CPAs have very high molecular weights (>> 450 g/mol) and require a wasteful

• listed above for the C2-symmetrical catalysts. First and foremost, the compounds must be inexpensive to make, which implies that their syntheses should be easily scaled. A modular synthesis is also desirable if some structure optimization is required. The resolution of the phosphorus center should be

• the catalysts With our various CPAs 2–4 in hand, their evaluation in asymmetric organocatalysis was conducted. The reaction could have been chosen from a tremendous number of possibilities [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. We selected the one Guinchard used to evaluate his

Supramolecular approaches to mediate chemical reactivity

• Pablo Ballester,
• Qi-Qiang Wang and
• Carmine Gaeta

Beilstein J. Org. Chem. 2022, 18, 1463–1465, doi:10.3762/bjoc.18.152

• reactions by a biomimetic approach [3][4]. Very recently, many efforts have been devoted to study supramolecular catalysis processes [5][6][7][8][9][10][11][12][13][14] in which macrocyclic hosts, self-assembled capsules and metallo-cages were employed as catalysts or nanocontainers. The primary

• catalysts were designed that showed substrate selectivity, turnover, regioselectivity, and stereoselectivity [5][6][7][8][9][10][11][12][13][14]. Supramolecular architectures with an internal cavity are potential candidates to work as supramolecular catalysts [5][6][7][8][9][10][11][12][13][14]. The first

• supramolecular catalysts were based on covalent hosts, typically cyclodextrin macrocycles [1], which had an interior hydrophobic cavity decorated with catalytically useful functional groups. Recently, increased emphasis has been placed on catalysis that takes use of noncovalent hosts, including self-assembled

Oxa-Michael-initiated cascade reactions of levoglucosenone

• Julian Klepp,
• Thomas Bousfield,
• Hugh Cummins,
• Sarah V. A.-M. Legendre,
• Jason E. Camp and
• Ben W. Greatrex

Beilstein J. Org. Chem. 2022, 18, 1457–1462, doi:10.3762/bjoc.18.151

• tetraketones 11 promoted by base (Scheme 2) [25]. The equivalent reaction has not been reported for dihydrolevoglucosenone (Cyrene™) 12, and it was thought that the chiral 1,5-diketone products could be used to construct catalysts or ligands. The aldol/Michael cascade using conditions for the aldol reaction

Dissecting Mechanochemistry III

• Lars Borchardt and
• José G. Hernández

Beilstein J. Org. Chem. 2022, 18, 1454–1456, doi:10.3762/bjoc.18.150

• were also key reagents to develop the mechanochemical halogenation of azobenzenes as studied by Ćurić and co-workers [4]. They demonstrated how, depending on the azobenzene structure, the halogenation of the C–H bonds with NBX occurred in the presence of Pd(II) catalysts or under metal-free conditions

• (Scheme 1b). Similarly, in the absence of metal catalysts, N-fluorobenzenesulfonimide (NFSI) was found to act as a mild fluorinating reagent for activated aromatics by mechanochemistry [5]. Such a collective effort to access halogenated substrates is understandable, owning the synthetic value of organic

• the use of halogenated compounds and include the mechanochemical preparation of isocyanides [10], formylated and acetylated amines [11], and the mechanosynthesis of unsymmetrical salens ligands for preparing metal–salen catalysts [12]. This illustrates the broad applicability of mechanochemical

Mechanochemical synthesis of unsymmetrical salens for the preparation of Co–salen complexes and their evaluation as catalysts for the synthesis of α-aryloxy alcohols via asymmetric phenolic kinetic resolution of terminal epoxides

• Shengli Zuo,
• Shuxiang Zheng,
• Jianjun Liu and
• Ang Zuo

Beilstein J. Org. Chem. 2022, 18, 1416–1423, doi:10.3762/bjoc.18.147

• scope and the need of Lewis acidic or basic co-catalysts [22][23][24]. A more efficient preparation of Co–salen catalysts is therefore of a great need for the asymmetric ring opening of epoxides, and thus became extremely attractive to us. The synthesis of novel Co–salen catalysts begins with the design

• reaction and stirred for 18 hours at 0 °C. Upon the reaction completion, 3-chloro-1,2-propanediol in highly enantioenriched structure was afforded using chiral catalyst 2f, while non-chiral catalysts 2e and 2g displayed nonenantioselective results (Table 2). To broaden the use of our chiral catalyst, α

• epichlorohydrin and provided α-aryloxy alcohols in an overall high yield and a complete enantioselectivity. Conclusion In summary, we mechanochemically synthesized unsymmetrical salens 1 for preparing metal–salen catalysts 2 for the first time. The use of grinding technology provided salens 1 in an overall higher

Synthesis of meso-pyrrole-substituted corroles by condensation of 1,9-diformyldipyrromethanes with pyrrole

• Baris Temelli and
• Pinar Kapci

Beilstein J. Org. Chem. 2022, 18, 1403–1409, doi:10.3762/bjoc.18.145

• reaction conditions and catalysts, unidentified product mixtures were obtained instead of corrole products in both reactions. Then, the reaction of 1,9-diformyl-5-phenyldipyrromethane (1a) in an excess amount of pyrrole was tested to obtain pyrrole-substituted metal-free corrole through the oxidation of

• the bilane intermediate by using DDQ (Scheme 2). Pyrrole was used as both reagent and solvent in these reactions. The desired product was not observed in the reaction medium when various catalysts (TFA, I2, AlCl3, InCl3, FeCl3, H2SO4, p-TsOH, Mont. KSF, Mont. K-10, and AgOTf) were used at different

• positive effect on the reaction yield (Table 1, entries 14 and 15), p-chloranil formed a product with a lower yield than DDQ (Table 1, entries 16–18). The activities of different copper catalysts were also tested in the model reaction. Only CuCl2 formed the product in 5% yield and the other salts did not

Synthesis of C6-modified mannose 1-phosphates and evaluation of derived sugar nucleotides against GDP-mannose dehydrogenase

• Sanaz Ahmadipour,
• Alice J. C. Wahart,
• Jonathan P. Dolan,
• Laura Beswick,
• Chris S. Hawes,
• Robert A. Field and
• Gavin J. Miller

Beilstein J. Org. Chem. 2022, 18, 1379–1384, doi:10.3762/bjoc.18.142

• deprotection with concomitant azide reduction was completed using hydrogen and Pd/C and Pd(OH)2/C catalysts, affording 13 as the disodium salt in 90% yield, after anion exchange chromatography. Synthesis of 6-deoxy-6-thio-ᴅ-mannose 1-phosphate (18) was completed from 14 via C6 substitution with thioacetate and

Cyclodextrin-based Schiff base pro-fragrances: Synthesis and release studies

• Attila Palágyi,
• Jindřich Jindřich,
• Juraj Dian and
• Sophie Fourmentin

Beilstein J. Org. Chem. 2022, 18, 1346–1354, doi:10.3762/bjoc.18.140

• influence of adding hygroscopic salts (MgSO4, LiClO4, or Ca(ClO4)2), triethyl orthoformate, or activated molecular sieves to the reaction. These compounds could function as desiccants removing the water formed during the reaction, as well as catalysts; nevertheless, the conversion to the final imine needed

Synthesis and electrochemical properties of 3,4,5-tris(chlorophenyl)-1,2-diphosphaferrocenes

• Almaz A. Zagidullin,
• Farida F. Akhmatkhanova,
• Mikhail N. Khrizanforov,
• Robert R. Fayzullin,
• Tatiana P. Gerasimova,
• Ilya A. Bezkishko and
• Vasili A. Miluykov

Beilstein J. Org. Chem. 2022, 18, 1338–1345, doi:10.3762/bjoc.18.139

• -acceptor properties closer to phosphites P(OR)3 [8][9]. Since the P atom in phosphaferrocenes retains an electron lone pair, phosphaferrocenes have been used as P-donor ligands [10][11][12] as well as nucleophilic catalysts [13][14]. Recently, the pentaphosphaferrocene Cp*Fe(η5-P5) has been used as a

B–N/B–H Transborylation: borane-catalysed nitrile hydroboration

• Filip Meger,
• Alexander C. W. Kwok,
• Franziska Gilch,
• Dominic R. Willcox,
• Alex J. Hendy,
• Kieran Nicholson,
• Andrew D. Bage,
• Thomas Langer,
• Thomas A. Hunt and
• Stephen P. Thomas

Beilstein J. Org. Chem. 2022, 18, 1332–1337, doi:10.3762/bjoc.18.138

• ]. Traditionally, the reduction of nitriles to primary amines relied on stoichiometric hydride reagents [4]. Current catalytic methods for nitrile reduction, hydrogenation [5][6] or hydroboration [7][8], generally rely on metal catalysts, designer ligands, forcing reaction conditions (such as elevated temperatures

• research into the development of new catalytic methodologies, specifically those that use Earth-abundant and low toxicity elements, as an alternative to transition-metal catalysis [9][10]. Using metal-free catalytic systems, including boron-based catalysts, circumvents some of the issues associated with

• strategies [27]. Both of these used non-commercially available catalysts prepared over multiple steps, the first an N-heterocyclic olefin [22], and the second a bicyclic (alkyl)(amino)carbine [23]. Both displayed limited tolerance to reducible functionalities. NaHBEt3 is the only known boron-based catalyst

Polymer and small molecule mechanochemistry: closer than ever

• José G. Hernández

Beilstein J. Org. Chem. 2022, 18, 1225–1235, doi:10.3762/bjoc.18.128

• , ideas on how polymer mechanochemistry could bias small molecule reactions were instantaneously provided by Prof. Stephen Craig [15], which included the possibility to mechanically control catalytic cycles in the future by switching the state of reactants or catalysts. Some approximations to this

Enzymes in biosynthesis

• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2022, 18, 1131–1132, doi:10.3762/bjoc.18.116

• the molecular scaffolds of natural products [5]. During the past two decades, large amounts of genome information from thousands of organisms have become available. This allows scientists today to gain direct access to the encoded catalysts through expression in easy-to-handle heterologous hosts, such

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

• catalytic approaches [9]. Especially the combination with other transition metal catalysts (metallaphotoredox catalysis), such as nickel complexes, resulted in a vast number of new methods to achieve cross-couplings under mild conditions [10]. However, the conditions of these methods are often hard to

• translate to flow [11][12] and significant changes to the optimized batch protocol are usually required [13][14]. The most common obstacle in the batch-to-flow translation of metallaphotoredox reactions is their frequent heterogeneous nature, most commonly due to poorly soluble inorganic bases, catalysts or

• additives [5][15]. Solid reagents and catalysts cause severe problems, such as reactor clogging under continuous-flow conditions. To prevent reactor fouling in (gas-)solid-liquid heterogeneous photoreactions, different solutions have been proposed [16], including the use of serial micro-batch reactors (SMBR

A Streptomyces P450 enzyme dimerizes isoflavones from plants

• Run-Zhou Liu,
• Shanchong Chen and
• Lihan Zhang

Beilstein J. Org. Chem. 2022, 18, 1107–1115, doi:10.3762/bjoc.18.113

• [1][10][11][12][13][14]. In plants and fungi, laccases and cytochrome P450 monooxygenases play pivotal roles in the biaryl bond formation of various polyketide dimers [10][15][16]. In contrast, in bacteria, P450 enzymes are the dominant catalysts, but no laccases have been reported for dimerization

Scope of tetrazolo[1,5-a]quinoxalines in CuAAC reactions for the synthesis of triazoloquinoxalines, imidazoloquinoxalines, and rhenium complexes thereof

• Laura Holzhauer,
• Chloé Liagre,
• Olaf Fuhr,
• Nicole Jung and
• Stefan Bräse

Beilstein J. Org. Chem. 2022, 18, 1088–1099, doi:10.3762/bjoc.18.111

• diversity of metal complexes incorporating 1,2,3-triazoles as ligands have been reported [16][17][18]. Triazole ligands with N-heterocycles such as Pyta (4-(2-pyridyl)-1,2,3-triazole) and related structures were employed to obtain novel metal complexes as catalysts [19][20] and imaging probes [21], as well

• suppressed in some cases when increasing the alkyne concentration drastically. The denitrogenative annulation reaction was then further explored using derivate 11d regarding the influences of different catalysts and additives (for details and results see Supporting Information File 1, Tables S3 and S4

• especially used as CO2 reduction catalysts [38][39][40] and noninvasive imaging probes [12][41]; examples for the application in organic light-emitting diodes [35] and as photoactive CO-releasing molecule [42][43] have been reported as well. For the complexation experiments, compounds with three different