Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

• Michio Yamada

Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13

• wormlike nanoparticles. In rotaxanes, the utilization of metal–ligand bonding involving CuI is a common strategy for immobilizing a thread moiety within a macrocycle. However, the efficacy of such a bonding is compromised when catalysts are used in stoppering reactions, e.g., the copper-catalyzed azide

Visible-light-induced radical cascade cyclization: a catalyst-free synthetic approach to trifluoromethylated heterocycles

• Chuan Yang,
• Wei Shi,
• Jian Tian,
• Lin Guo,
• Yating Zhao and
• Wujiong Xia

Beilstein J. Org. Chem. 2024, 20, 118–124, doi:10.3762/bjoc.20.12

• radicals. This method allows the efficient synthesis of various indole derivatives without the need of photocatalysts or transition-metal catalysts. Mechanism experiments indicate that the process involves a radical chain process initiated by the homolysis of Umemoto's reagent. This straightforward method

• ], Friedel–Crafts acylation [12], radical cascade reactions [2][13], and photoinduced radical cyclizations [14][15][16][17]. However, these methods often suffer from drawbacks such as harsh reaction conditions and the requirement of transition-metal catalysts. Although photocatalyzed cyclization reactions

• usually occur under mild conditions, they typically require expensive metal-based photocatalysts or structurally complex organic dyes [18]. Therefore, the development of a photoinduced cascade reaction without the need of additional catalysts or additives remains highly desirable [19]. The introduction of

Using the phospha-Michael reaction for making phosphonium phenolate zwitterions

• Matthias R. Steiner,
• Max Schmallegger,
• Larissa Donner,
• Johann A. Hlina,
• Christoph Marschner,
• Judith Baumgartner and
• Christian Slugovc

Beilstein J. Org. Chem. 2024, 20, 41–51, doi:10.3762/bjoc.20.6

• powerful tool for performing organic reactions [1] and polymerizations [2]. In this context phosphines have proven to be potent Lewis-base catalysts [3][4] for a variety of reactions [5], including but not limited to Rauhut–Currier [6], Morita–Baylis–Hillman [7], and Michael reactions [8][9][10]. In all

• this zwitterion formation is of great importance since it is the initiation step for the catalytic cycle in Michael reactions [8]. Generally, the conjugate addition is favored for strong nucleophiles, which is why electron-rich trialkylphosphines were among the first catalysts used in this type of

• trifluoromethyl groups [20] and the cross-coupling of aryl halides [21]. Like phosphonium salts in general are used as catalysts [22][23], phosphonium salts based on ortho-hydroxy-substituted phosphines received particular attention because of their zwitterionic nature and have been used as catalysts in the

Synthesis of N-acyl carbazoles, phenoxazines and acridines from cyclic diaryliodonium salts

• Nils Clamor,
• Mattis Damrath,
• Thomas J. Kuczmera,
• Daniel Duvinage and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2024, 20, 12–16, doi:10.3762/bjoc.20.2

• [33][34]. Results and Discussion Initially, we investigated the synthesis of N-acyl carbazole by treatment of diaryliodonium salt 1a with valeramide using Cu(I) catalysts [18]. The results are shown in Table 1. In the first experiments in p-xylene at 120 °C with DMEDA as N,N-ligand, only modest

1-Butyl-3-methylimidazolium tetrafluoroborate as suitable solvent for BF₃: the case of alkyne hydration. Chemistry vs electrochemistry

• Marta David,
• Elisa Galli,
• Richard C. D. Brown,
• Marta Feroci,
• Fabrizio Vetica and
• Martina Bortolami

Beilstein J. Org. Chem. 2023, 19, 1966–1981, doi:10.3762/bjoc.19.147

• , UK Department of Chemistry, Sapienza University of Rome, piazzale Aldo Moro, 5, 00185 Rome, Italy 10.3762/bjoc.19.147 Abstract In order to replace the expensive metal/ligand catalysts and classic toxic and volatile solvents, commonly used for the hydration of alkynes, the hydration reaction of

• stimulated the search for alternative catalysts and conditions for the hydration of alkynes, in order to identify safer and more sustainable methods [11][12][13]. In particular, transition-metal catalysts containing Au(I) or (III) [14][15][16][17][18][19][20][21][22][23][24], Ru(II) [25][26][27][28][29][30

• ], Pd(II) [31][32][33], Pt(II) [34][35], Fe(III) [36][37], Cu(I) [38][39][40][41], Co(III) [42][43][44], as well as other metals, have been widely studied. In addition, methods involving Brønsted acids, alone or in presence of Lewis acids as co-catalysts, have been developed [45][46][47][48][49][50][51

Aldiminium and 1,2,3-triazolium dithiocarboxylate zwitterions derived from cyclic (alkyl)(amino) and mesoionic carbenes

• Nedra Touj,
• François Mazars,
• Guillermo Zaragoza and
• Lionel Delaude

Beilstein J. Org. Chem. 2023, 19, 1947–1956, doi:10.3762/bjoc.19.145

• heterocycles; zwitterions; Introduction Following the seminal discovery from the group of Arduengo, who isolated and fully characterized 1,3-di(1-adamantyl)imidazol-2-ylidene in 1991 [1], stable divalent carbon species have evolved from fleeting intermediates to ubiquitous catalysts, ligands, and reagents in

• variety of small molecules and to bind strongly to metal centers, thereby affording very robust catalysts [9][10][11][12]. Another category of stable carbenes that has emerged in the new millennium is made of mesoionic compounds, for which no reasonable canonical resonance form can be drawn in the absence

Beyond n-dopants for organic semiconductors: use of bibenzo[d]imidazoles in UV-promoted dehalogenation reactions of organic halides

• Kan Tang,
• Megan R. Brown,
• Chad Risko,
• Melissa K. Gish,
• Garry Rumbles,
• Phuc H. Pham,
• Oana R. Luca,
• Stephen Barlow and
• Seth R. Marder

Beilstein J. Org. Chem. 2023, 19, 1912–1922, doi:10.3762/bjoc.19.142

• -containing catalysts [32]. We note that another all-organic reductive dimerization of benzyl halides using 2,3,5,6-tetrakis(tetramethylguanidino)pyridine has recently been reported [37]. The less readily reduced halides examined here (1d,e, and 2) are only sluggishly converted, even when using both (N-DMBI)2

Anion–π catalysis on carbon allotropes

• M. Ángeles Gutiérrez López,
• Mei-Ling Tan,
• Giacomo Renno,
• Augustina Jozeliūnaitė,
• J. Jonathan Nué-Martinez,
• Javier Lopez-Andarias,
• Naomi Sakai and
• Stefan Matile

Beilstein J. Org. Chem. 2023, 19, 1881–1894, doi:10.3762/bjoc.19.140

• because it took some time to find the benchmark reaction needed to develop the catalysts (Figure 2) [2]. With this operational enolate chemistry in hand, it quickly became clear that increasing π acidity at the same time decreases the stability of the catalyst [3][4][5]. This suggested that induced rather

• than intrinsic anion–π interactions should provide access to really strong catalysts [3]. They have been predicted theoretically to occur on π-stacks [6], and confirmed recently to exist and apply to anion–π catalysis on π-stacked foldamers (Figure 1B) [7] and micelles [8]. However, due to their unique

• ][56][57]. Anion–π catalysis on fullerenes has been introduced in 2017 [12]. Fullerene anion–π catalysts were developed with the benchmark reaction introduced two years earlier (Figure 2) [2]. In this reaction, at the beginning of all biosynthesis, finetuned malonic acid half thioesters 4 [58][59][60

N-Boc-α-diazo glutarimide as efficient reagent for assembling N-heterocycle-glutarimide diads via Rh(II)-catalyzed N–H insertion reaction

• Grigory Kantin,
• Pavel Golubev,
• Alexander Sapegin,
• Alexander Bunev and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2023, 19, 1841–1848, doi:10.3762/bjoc.19.136

• ), up to 2–3 days, along with the addition of an extra portion or two of catalyst to complete the reaction. Furthermore, the yields of the NH-insertion products in the latter reactions were moderate or low (see 6h, 6r, 6s, Scheme 3). It should be noted that we have also tested some Cu(II) catalysts (Cu

• decreased (62% (NMR) vs 69% (isolated)). When Rh2(TFA)4 (1 mol %) was used, a reversal of the ratio of 6a/9a insertion products (1:2) was observed in the test reaction, although the total yield estimated by NMR was only 32%. Thus, in the series of tested Rh(II) catalysts Rh2(esp)2 is the most successful

Substituent-controlled construction of A₄B₂-hexaphyrins and A₃B-porphyrins: a mechanistic evaluation

• Seda Cinar,
• Dilek Isik Tasgin and
• Canan Unaleroglu

Beilstein J. Org. Chem. 2023, 19, 1832–1840, doi:10.3762/bjoc.19.135

• porphyrins were detected in the mass spectra of some of the products. 1H NMR analysis of the synthesized hexaphyrins proved that the spectra were in consistence with [26]hexaphyrin aromaticity [29]. Several other metal triflates such as Zn(OTf)2, Gd(OTf)3, and Yb(OTf)3 were also tested as catalysts in the

A novel recyclable organocatalyst for the gram-scale enantioselective synthesis of (S)-baclofen

• Gyula Dargó,
• Dóra Erdélyi,
• Balázs Molnár,
• Péter Kisszékelyi,
• Zsófia Garádi and
• József Kupai

Beilstein J. Org. Chem. 2023, 19, 1811–1824, doi:10.3762/bjoc.19.133

• Budapest, Hungary 10.3762/bjoc.19.133 Abstract Synthesizing organocatalysts is often a long and cost-intensive process, therefore, the recovery and reuse of the catalysts are particularly important to establish sustainable organocatalytic transformations. In this work, we demonstrate the synthesis

• achieved, for example, by immobilizing the catalysts to a solid support [15], e.g., silica gel [16][17][18], organic polymers [19][20][21], magnetic nanoparticles [22][23], or by membrane separation, e.g., using organic solvent nanofiltration (OSN) [24][25][26], which methods can be easily implemented in

• flow systems. Accordingly, the main recycling methods rely on the immobilization of catalysts on heterogeneous supports, however, this could often lead to the deterioration of activity and/or selectivity [27]. A possible solution to avoid these drawbacks is the heterogenization of the catalyst after a

Recent advancements in iodide/phosphine-mediated photoredox radical reactions

• Tinglan Liu,
• Yu Zhou,
• Junhong Tang and
• Chengming Wang

Beilstein J. Org. Chem. 2023, 19, 1785–1803, doi:10.3762/bjoc.19.131

• decarboxylative alkylation reaction that was facilitated by the synergistic action of a cost-effective and easily accessible NaI/PPh3 catalyst system (Scheme 1). This system offered an alternative to the use of precious metals or complex organic dyes as catalysts. The developed NaI/PPh3-based system not only

• of fused ketones 34, eliminating the need for transition-metal catalysts or oxidants. The technique offered a broad substrate scope, remarkable selectivity, and simple reaction conditions. A plausible mechanism had been proposed for the photocatalytic decarboxylative [3 + 2]/[4 + 2] annulation, as

Active-metal template clipping synthesis of novel [2]rotaxanes

• Cătălin C. Anghel,
• Teodor A. Cucuiet,
• Niculina D. Hădade and
• Ion Grosu

Beilstein J. Org. Chem. 2023, 19, 1776–1784, doi:10.3762/bjoc.19.130

• molecule which catalyzes the macrocyclization reaction around the axle (Figure 1b). Results and Discussion In order to access the target [2]rotaxanes we made use of the CuAAC reaction, performed in the presence of a copper(I) N-heterocyclic carbene, a very stable and efficient class of catalysts used in

Selectivity control towards CO versus H₂ for photo-driven CO₂ reduction with a novel Co(II) catalyst

• Lisa-Lou Gracia,
• Philip Henkel,
• Olaf Fuhr and
• Claudia Bizzarri

Beilstein J. Org. Chem. 2023, 19, 1766–1775, doi:10.3762/bjoc.19.129

• Karlsruhe Nano Micro Facility (KNMFi), Karlsruhe Institute of Technology (KIT), Kaiserstrasse 12, 76131 Karlsruhe, Germany 10.3762/bjoc.19.129 Abstract Developing efficient catalysts for reducing carbon dioxide, a highly stable combustion waste product, is a relevant task to lower the atmospheric

• purpose, three main components are needed: a photosensitizer (PS), which acts like a light-antennae harvesting system in natural photosynthesis, a catalyst (Cat.), reacting directly with CO2 after being reduced, and a sacrificial electron donor (SeD). When the involved (photo)catalysts are homogeneous

• ) intermediate could be favored concerning the formation of the CO2 adduct with the reduced metal center. Thus, besides the development of novel efficient catalysts, different strategies have been pursued to switch the catalyst selectivity towards carbon products [4][5]. Generally, scientists can interplay by

Benzoimidazolium-derived dimeric and hydride n-dopants for organic electron-transport materials: impact of substitution on structures, electrochemistry, and reactivity

• Swagat K. Mohapatra,
• Khaled Al Kurdi,
• Samik Jhulki,
• Georgii Bogdanov,
• John Bacsa,
• Maxwell Conte,
• Tatiana V. Timofeeva,
• Seth R. Marder and
• Stephen Barlow

Beilstein J. Org. Chem. 2023, 19, 1651–1663, doi:10.3762/bjoc.19.121

• condenses with the aldehyde but where the subsequent second condensation and oxidation does not take place, i.e., structures of type IV (Scheme 1), which are known to be converted to benzimidazoles by various oxidants and/or catalysts [30][31][32]. The benzimidazoles were then doubly methylated with

Radical chemistry in polymer science: an overview and recent advances

• Zixiao Wang,
• Feichen Cui,
• Yang Sui and
• Jiajun Yan

Beilstein J. Org. Chem. 2023, 19, 1580–1603, doi:10.3762/bjoc.19.116

• Grubbs catalysts (Scheme 12A), are the most popular ones [87]. However, Ru-based catalysts are expensive making them less attractive for industrial applications. Living ROMP is commonly terminated by adding a special chemical which can remove the transition metal from the chain end and deactivate it from

• couplings in PATs. Scheme 10 redrawn from [79]. General thiol-ene photopolymerization process. Scheme 11 redrawn from [81]. (a) Three generations of Grubbs catalysts. (b) Proposed mechanism for photo-ROMP via a reductive quenching pathway and (c, d) chemical structures of the (c) initiators and (d) monomers

Lewis acid-promoted direct synthesis of isoxazole derivatives

• Dengxu Qiu,
• Chenhui Jiang,
• Pan Gao and
• Yu Yuan

Beilstein J. Org. Chem. 2023, 19, 1562–1567, doi:10.3762/bjoc.19.113

• nitrogen source (Scheme 1, reaction 2). In 2017, Xu and co-workers [19] developed a copper-mediated annulation reaction to synthesize isoxazoles from two different alkynes. In fact, most methods mostly used highly toxic transition-metal catalysts such as copper metals. In order to develop cheaper and more

• environmentally friendly catalysts, our laboratory recently developed an alternative approach to the synthesis of isooxazoles starting from 2-methylquinoline and alkynes mediated by Brønsted acids in good yields (Scheme 1, reaction 3) [20]. The utilization of main element metal aluminum salts in organic synthesis

Morpholine-mediated defluorinative cycloaddition of gem-difluoroalkenes and organic azides

• Tzu-Yu Huang,
• Mario Djugovski,
• Sweta Adhikari,
• Destinee L. Manning and
• Sudeshna Roy

Beilstein J. Org. Chem. 2023, 19, 1545–1554, doi:10.3762/bjoc.19.111

• hypothesis, we observed that p-cyanophenyl azide (2b) gave a better yield (30%, Table 1, entry 2) compared to the unsubstituted phenyl azide (2a, 21% yield, entry 1). Among the nickel catalysts screened, NiCl2(dppp)2 gave a better yield (Table 1, entry 2 vs entry 3). K3PO4 was used as a base since it has

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

• Fatemeh Doraghi,
• Seyedeh Pegah Aledavoud,
• Mehdi Ghanbarlou,
• Bagher Larijani and
• Mohammad Mahdavi

Beilstein J. Org. Chem. 2023, 19, 1471–1502, doi:10.3762/bjoc.19.106

• -coupling, and direct sulfenylation reactions, which are classified into three categories: sulfenylation catalyzed by i) transition metal catalysts, ii) organocompound catalysts, and iii) catalyst-free sulfenylation. Review Sulfenylation of organic compounds by N-(sulfenyl)succinimides/phthalimides Metal

• ) [44]. Among different Lewis acid catalysts, such as Cu(OTf)2, Mg(OTf)2, Zn(OTf)2, Sc(OTf)3, Eu(OTf)3, and Yb(OTf)3, it was found that Sc(OTf)3 gave higher product yield. In addition, the combination of Sc(OTf)3/ILs displayed good recyclability in this transformation. In 2014, Anbarasan and Saravanan

• as a sulfenylating source gave the target product in 93% yield. Knochel and co-workers found that copper acetate can catalyze the cross-coupling reaction between (hetero)aryl, alkyl and benzylic zinc halides 36 with N-thiophthalimides 14 (Scheme 18) [55]. Various metal catalysts, including CrCl2

Application of N-heterocyclic carbene–Cu(I) complexes as catalysts in organic synthesis: a review

• Nosheen Beig,
• Varsha Goyal and
• Raj K. Bansal

Beilstein J. Org. Chem. 2023, 19, 1408–1442, doi:10.3762/bjoc.19.102

• the metal to the π* orbital of the NHC. Over the last two decades, NHC–metal complexes have been extensively used as efficient catalysts in different types of organic reactions. Of these, NHC–Cu(I) complexes found prominence for various reasons, such as ease of preparation, possibility of structural

• diversity, low cost, and versatile applications. This article overviews applications of NHC–Cu(I) complexes as catalysts in organic synthesis over the last 12 years, which include hydrosilylation reactions, conjugate addition, [3 + 2] cycloaddition, A3 reaction, boration and hydroboration, N–H and C(sp2)–H

• 12 years, i.e., from 2010 through 2022 only. Nevertheless, wherever necessary, earlier works may also be included to maintain coherence. Furthermore, in view of the enormous amount of research work done on NHC–metal complexes and their application as catalysts, the present review was restricted to

Visible-light-induced nickel-catalyzed α-hydroxytrifluoroethylation of alkyl carboxylic acids: Access to trifluoromethyl alkyl acyloins

• Feng Chen,
• Xiu-Hua Xu,
• Zeng-Hao Chen,
• Yue Chen and
• Feng-Ling Qing

Beilstein J. Org. Chem. 2023, 19, 1372–1378, doi:10.3762/bjoc.19.98

• of H2O were added to the reaction mixture [40] (Table 1, entry 6), but the addition of more water did not improve the reaction efficiency further (Table 1, entry 7). The structure of nickel catalysts played a significant role in the reaction efficiency. Switching the Ni catalyst to NiCl2(dtbbpy

Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp³)–H to construct C–C bonds

• Hui Yu and
• Feng Xu

Beilstein J. Org. Chem. 2023, 19, 1259–1288, doi:10.3762/bjoc.19.94

• become a major strategy for ether functionalization. This review covers C–H/C–H cross-coupling reactions of ether derivatives with various C–H bond substrates via non-noble metal catalysts (Fe, Cu, Co, Mn, Ni, Zn, Y, Sc, In, Ag). We discuss advances achieved in these CDC reactions and hope to attract

• overcome the shortcomings of the above coupling reactions, organic chemists have envisaged the construction of C–C bonds directly through C–H bond activation [5]. Fortunately, scientists have used various transition metals as catalysts to realize the activation of various types of C–H bonds, and have

• significantly different reactivity and chemical selectivity from noble metals (Ru, Rh, Pd). Compared with noble metals, copper catalysts are cheaper and easier to obtain, making Cu more advantageous for industrial applications of C–H functionalization reactions. The Glaser–Hay reaction may be one of the oldest

Metal catalyst-free N-allylation/alkylation of imidazole and benzimidazole with Morita–Baylis–Hillman (MBH) alcohols and acetates

• Olfa Mhasni,
• Jalloul Bouajila and
• Farhat Rezgui

Beilstein J. Org. Chem. 2023, 19, 1251–1258, doi:10.3762/bjoc.19.93

• reflux with an azeotropic distillation, was successfully carried out with no catalysts or additives, affording the corresponding N-substituted imidazole derivatives in good yields. On the other hand, in refluxing toluene or methanol, the aza-Michael addition of imidazole onto acyclic MBH alcohols was

• these substrates and the formation of water as the sole non-toxic byproduct in the reaction [11]. In general, the previous methods for the amination of MBH alcohols needed catalysts or additives such as FeCl3 [12][13], In(OTf)3 [14], MoCl5 [15], AuCl3 [16], and I2 [17] as Lewis acids. Alternatively

• 2a and 2b as nucleophilic reagents without catalysts or activating agents (Scheme 1, reaction 2), or from acyclic MBH alcohols 1 using DABCO as a powerful nucleophilic additive (Scheme 1, reaction 3). Results and Discussion In our first investigations, we selected the reaction of the primary acetate

Radical ligand transfer: a general strategy for radical functionalization

• David T. Nemoto Jr,
• Kang-Jie Bian,
• Shih-Chieh Kao and
• Julian G. West

Beilstein J. Org. Chem. 2023, 19, 1225–1233, doi:10.3762/bjoc.19.90

• driven by several key features of RLT catalysis, including the ability to form diverse bonds (including C–X, C–N, and C–S), the use of simple earth abundant element catalysts, and the intrinsic compatibility of this approach with varied radical generation methods, including HAT, radical addition, and

• body’s own cytochrome P450 enzymes. These catalysts exhibit unique “radical rebound” reactivity at their heme active sites (Scheme 1) [12], a mechanism proposed by Groves and co-workers and heavily explored beginning in the 1970s [13][14]. This two-step functionalization sequence begins with HAT from an

• found to be capable of functionalizing specific C–H bonds to numerous functionalities, including C–F [21][22], C–N3 [23], and C–Cl bonds [24][25]. Upon these remarkable observations, methodologies involving manganese–porphyrin catalysts have been developed over the years. These methods take advantage of

Unravelling a trichloroacetic acid-catalyzed cascade access to benzo[f]chromeno[2,3-h]quinoxalinoporphyrins

• Chandra Sekhar Tekuri,
• Pargat Singh and
• Mahendra Nath

Beilstein J. Org. Chem. 2023, 19, 1216–1224, doi:10.3762/bjoc.19.89

• -diamino-5,10,15,20-tetra(p-tolyl)porphyrin (1) with 2-hydroxynaphthalene-1,4-dione, dimedone and benzaldehyde in the presence of different acidic catalysts such as p-toluenesulfonic acid (PTSA), La(OTf)3, ʟ-ascorbic acid, p-dodecylbenzenesulfonic acid (DBSA), trichloroacetic acid (TCA) and trifluoroacetic

• acid (TFA) in CHCl3 for 3 hours at 65 °C under one-pot operation (Table 1, entries 1–6). Surprisingly, the reaction did not proceed when La(OTf)3 and ʟ-ascorbic acid were used as acidic catalysts (Table 1, entries 2 and 3). In contrast, the use of Brønsted acidic catalysts such as DBSA and PTSA