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

Enabling artificial photosynthesis systems with molecular recycling: A review of photo- and electrochemical methods for regenerating organic sacrificial electron donors

• Grace A. Lowe

Beilstein J. Org. Chem. 2023, 19, 1198–1215, doi:10.3762/bjoc.19.88

• electron donors are usually small organic molecules which are used in large quantities and need to be cheap. This often means they are less optimized than expensive catalysts and dyes. However, systems that employ redox mediators can use lower concentrations of more expensive species. For example

• solvent polarity [24][25]. Hence, it is important when considering new reagents and catalysts to only compare potentials measured in conditions as close to the photocatalytic conditions as possible. For instance, quinones have 2 one-electron reductions in aprotic media and one two-electron reduction at a

• by Girault, Scanlon and co-workers on photocatalytic water splitting [33][34][35]. They used the redox mediator decamethylferrocene (DcMFc) in biphasic systems and semi-immobilized their photosensitizers and catalysts at interfaces between two immiscible electrolyte solutions (ITIES). This

Exploring the role of halogen bonding in iodonium ylides: insights into unexpected reactivity and reaction control

• Carlee A. Montgomery and
• Graham K. Murphy

Beilstein J. Org. Chem. 2023, 19, 1171–1190, doi:10.3762/bjoc.19.86

• ][78][79][80][81][82]. Organocatalysis is also a common point of intersection for halogen- and hydrogen bonding, and this has been thoroughly explored using monovalent iodine catalysts [83][84][85]. 1.3 Halogen bonding in hypervalent iodine complexes Similar to monovalent iodine compounds, a diverse

• cycloaddition reactions that occur without transition metal catalysts, the unexpected initiation of single electron transfer (SET) processes or photochemical transformations, and even proton transfers that appear to defy pKa limitations. The reaction pathways followed by iodonium ylides and Lewis basic reaction

• was presumed to play a central role in these metal-free processes. Various cycloaddition reactions of iodonium ylides that were typically associated with metallocarbene-mediated processes were also operative in the absence of catalysts. The mild reaction conditions precluded researchers from proposing

Selective and scalable oxygenation of heteroatoms using the elements of nature: air, water, and light

• Damiano Diprima,
• Hannes Gemoets,
• Stefano Bonciolini and
• Koen Van Aken

Beilstein J. Org. Chem. 2023, 19, 1146–1154, doi:10.3762/bjoc.19.82

• [23][24] and methods for oxidation such as photochemistry, or electrochemistry have been developed [2][25]. However, low selectivity and the need for appropriate catalysts that are stable, cost-effective, and easy to remove remain problematic. Recently, catalyst-free procedures using O2 or air have

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

• UV region, side reactions and selectivity issues arise upon direct excitation of organic molecules. In recent years, two conceptually distinct but mechanistically related strategies have emerged that enable access to excited state catalysts wielding i) higher redox power than standard monophotonic

• photoredox catalysts and ii) energy that parallels the energy of UV-driven transformations, but under cheaper, safer conditions and in a more selective manner by indirect substrate activation via a catalyst. These are: a) multi-photon processes that accumulate visible light photon energies for electron

• , commercially available aryl halides are chlorides [37][38], with potentials for reduction that almost exclusively lie beyond the threshold of monophotonically-excited photoredox catalysts (i.e., more deeply negative than E1/2 = −2.0 V vs SCE). Considering this, state-of-the-art developments have focused on the

Copper-catalyzed N-arylation of amines with aryliodonium ylides in water

• Kasturi U. Nabar,
• Bhalchandra M. Bhanage and
• Sudam G. Dawande

Beilstein J. Org. Chem. 2023, 19, 1008–1014, doi:10.3762/bjoc.19.76

• strategies for C–N bond formation have been extensively explored by various research groups for the N-arylation of amines. Specifically, seminal contributions by Buchwald [15] and Hartwig [16] involving the use of palladium complexes as catalysts in the presence of either phosphine or diamine ligands for C–N

• bond formation. However, these methods suffer from limitations such as moisture sensitivity, the requirement of specific ligands, and the use of expensive palladium catalysts [17]. Also, Chan Lam, Evans, and other research groups have developed copper-catalyzed C–N bond formation reactions by careful

• straightforward and efficient method for the N-arylation of primary arylamines and secondary amines with 1,3-cyclohexanedione-derived aryliodonium ylides in the presence of copper catalysts in water as a solvent. Results and Discussion To test our hypothesis, we commenced our studies by treatment of aniline (1a

Aromatic C–H bond functionalization through organocatalyzed asymmetric intermolecular aza-Friedel–Crafts reaction: a recent update

• Anup Biswas

Beilstein J. Org. Chem. 2023, 19, 956–981, doi:10.3762/bjoc.19.72

• groups into the aromatic ring. This reaction has a great scope of forming aza-stereocenters which can be tuned by different asymmetric catalysts. This review assembles recent advances in asymmetric aza-Friedel–Crafts reactions mediated by organocatalysts. The mechanistic interpretation with the origin of

• bond is thermodynamically stable and possesses a high bond dissociation energy opposing the bond to easy chemical transformation. Therefore, harsh reaction conditions and the necessity of an external activator like catalysts are common prerequisites for processes involving C–H bond breaking. Among

• the tremendous progress in organic chemistry over the last few decades, metal catalysis has been increasingly and successfully replaced by organocatalysis, i.e., accelerating the rate of chemical transformations by using small organic molecules as catalysts. Although being discovered more than 100

Clauson–Kaas pyrrole synthesis using diverse catalysts: a transition from conventional to greener approach

• Dileep Kumar Singh and
• Rajesh Kumar

Beilstein J. Org. Chem. 2023, 19, 928–955, doi:10.3762/bjoc.19.71

• acid catalysts and transition metal catalysts. The goal of this review is to summarize the synthesis of various N-substituted pyrrole derivatives using a modified Clauson–Kaas reaction under diverse conventional and greener reaction conditions. Keywords: catalyst; Clauson–Kaas pyrrole synthesis; 2,5

• . Furthermore, many solvent-free reactions and solid-supported reagents are becoming increasingly popular in organic synthesis. Moreover, in order to increase the product yield, different green catalysts were used in the synthesis of numerous organic and bioorganic molecules while reducing the amount of excess

• -dialkoxytetrahydrofuran. This reaction was originally discovered by N. Clauson–Kaas and Z. Tyle in 1952 [37] (Scheme 2a). Initially, acetic acid was used as a catalyst in this classic reaction; however, diverse modifications have been reported for this procedure using various Brønsted acid catalysts, metal catalysts, and

Synthesis of aliphatic nitriles from cyclobutanone oxime mediated by sulfuryl fluoride (SO₂F₂)

• Xian-Lin Chen and
• Hua-Li Qin

Beilstein J. Org. Chem. 2023, 19, 901–908, doi:10.3762/bjoc.19.68

• ], Liu [35], and Yang [36] achieved similar transformations through visible-light photocatalysis. In addition, Guo [37][38] improved the protocol by using low-cost nickel and iron catalysts. However, most of these advancements mainly relied on the excellent redox potential manipulation of cyclic oxime

• 1,4-dioxane the transformations performed the best (Table 1, entries 3–5). A series of copper catalysts such as CuI, CuCN, and Cu2O was screened, in which some showed good catalytic activity (Table 1, entries 6–9), and Cu2O was identified as the most effective catalyst for the desired transformation

Cyclodextrins as building blocks for new materials

• Miriana Kfoury and
• Sophie Fourmentin

Beilstein J. Org. Chem. 2023, 19, 889–891, doi:10.3762/bjoc.19.66

• , and so on [14][15][16][17]. In addition to bearing a rigid skeleton, CDs act as versatile multitasking agents. They add value to these composites as their cavities remain generally available to accommodate active substances, or they work as supramolecular catalysts or molecular concealers. Due to the

Pyridine C(sp²)–H bond functionalization under transition-metal and rare earth metal catalysis

• Haritha Sindhe,
• Malladi Mounika Reddy,
• Karthikeyan Rajkumar,
• Akshay Kamble,
• Amardeep Singh,
• Anand Kumar and
• Satyasheel Sharma

Beilstein J. Org. Chem. 2023, 19, 820–863, doi:10.3762/bjoc.19.62

• providing various ortho-aminoalkylated products 36 whereas ortho-alkylated pyridine derivatives 38 were obtained when using NP1-Sc as the catalyst (Scheme 8). Attributing to the strong coordination of unsubstituted pyridine with Rh(I) catalysts, C–H alkylations of pyridine lacking ortho-blocking groups is a

• catalyst using 2-arylpyridines (Scheme 15). Earlier reports described the propenylation took place on the ortho-position of the phenyl ring [76][77], whereas this group achieved the propenylation of the pyridine moiety. The authors screened different allyl halides and Ru complexes as catalysts. With the

• . Also, metal–NHC complexes have wide application in catalysis and various organic transformations and a range of metal–NHCs served as catalysts. In 2010, using NHC ligands, Yap and co-workers [90] developed a method for the direct para and meta-C–H alkenylation of pyridines with 4-octyne (107) using a

Sulfate radical anion-induced benzylic oxidation of N-(arylsulfonyl)benzylamines to N-arylsulfonylimines

• Joydev K. Laha,
• Pankaj Gupta and
• Amitava Hazra

Beilstein J. Org. Chem. 2023, 19, 771–777, doi:10.3762/bjoc.19.57

• condensation of aromatic aldehydes and sulfonamides (Scheme 1a) [3][5][6][7][8]. Because of the poor nucleophilicity of sulfonamides, the condensation reactions generally require harsh reaction conditions involving the use of strong acids, elevated temperature, and metal catalysts. Other methods include a non

• CrO2 [9], PhI(OAc)2/I2 [10], TEMPO [11], NHPI [12], and metal catalysts [13], suffer from serious limitations including the use of metal catalysts, high temperature, risk of explosive hazards, production of large waste, and often low yield (Scheme 1c). Thus, an environmentally benign method that could

Honeycomb reactor: a promising device for streamlining aerobic oxidation under continuous-flow conditions

• Masahiro Hosoya,
• Yusuke Saito and
• Yousuke Horiuchi

Beilstein J. Org. Chem. 2023, 19, 752–763, doi:10.3762/bjoc.19.55

• , conversion, yield and availability of the catalysts. Because the honeycomb reactor is made of porous material, the homogeneous reaction solution is a key factor. Stahl and Steves have developed a highly reactive aerobic oxidation [38]. This promising methodology enables completion of the reaction in 30 min

• at room temperature (Table 1, entry 1). However, four kinds of catalysts were used, and a simpler catalytic system would be preferable. The highly reactive catalyst, 9-azanoradamantane N-oxyl (nor-AZADO), was tried with NaNO2 as a cocatalyst, which resulted in completion of the reaction in 60 min

• (Table 1, entry 2) [39]. While this led to a simpler catalyst system, nor-AZADO is expensive. Hong and co-workers have developed a low-cost catalyst system using TEMPO and nitrate salts [40]. Fe(NO3)3 (Table 1, entry 3), Cu(NO3)2 (Table 1, entry 4), Zn(NO3)2 (Table 1, entry 5) worked as catalysts

Strategies in the synthesis of dibenzo[b,f]heteropines

• David I. H. Maier,
• Barend C. B. Bezuidenhoudt and
• Charlene Marais

Beilstein J. Org. Chem. 2023, 19, 700–718, doi:10.3762/bjoc.19.51

• commercial antidepressants, anxiolytics and anticonvulsants, but also in reengineering for other applications. More recently, the potential of the dibenzo[b,f]azepine moiety in organic light emitting diodes and dye-sensitized solar cell dyes has been recognised, while catalysts and molecular organic

• transition metal (Ni, Fe, V) porphyrin catalysts and oxygen. Catalytic reduction (H2, Pd/C) affords 2,2'-diaminobibenzyl (20) in the subsequent step [28]. 1.2 Ring-closing via amine condensation The initial synthesis of 10,11-dihydro-5H-dibenzo[b,f]azepine (2a) was reported in 1899 by Thiele and Holzinger

• . Knell et al. [40][41] reported a comparison of several catalysts, which included potassium-promoted iron, cobalt and manganese oxide catalysts, for the synthesis of 1a. Industrially, 1a is produced by the vapour phase dehydration of 2a over an iron/potassium/chromium catalyst system (Scheme 4) [42]. 2

pH-Responsive fluorescent supramolecular nanoparticles based on tetraphenylethylene-labelled chitosan and a six-fold carboxylated tribenzotriquinacene

• Nan Yang,
• Yi-Yan Zhu,
• Wei-Xiu Lin,
• Yi-Long Lu and
• Wen-Rong Xu

Beilstein J. Org. Chem. 2023, 19, 635–645, doi:10.3762/bjoc.19.45

• extensive attention owing to their potential applications in biomedicine, chemical sensing and as catalysts [1][2]. It is possible to regulate the formation and breakdown of supramolecular structures using external stimuli, such as pH, light, temperature, enzymes, and competing reagents [3][4]. Among these

Enolates ambushed – asymmetric tandem conjugate addition and subsequent enolate trapping with conventional and less traditional electrophiles

• Péter Kisszékelyi and
• Radovan Šebesta

Beilstein J. Org. Chem. 2023, 19, 593–634, doi:10.3762/bjoc.19.44

• sequence, were isolated in moderate to good yields and with high enantiopurities. Continuing with other Rh-based catalysts, the group of Lautens has also studied the stereoselective conjugate addition of alkynyl species to α,β-unsaturated ketones with subsequent trapping of the metal enolate by aldol

C3-Alkylation of furfural derivatives by continuous flow homogeneous catalysis

• Grédy Kiala Kinkutu,
• Catherine Louis,
• Myriam Roy,
• Juliette Blanchard and
• Julie Oble

Beilstein J. Org. Chem. 2023, 19, 582–592, doi:10.3762/bjoc.19.43

• .19.43 Abstract The C3-functionalization of furfural using homogeneous ruthenium catalysts requires the preinstallation of an ortho-directing imine group, as well as high temperatures, which did not allow scaling up, at least under batch conditions. In order to design a safer process, we set out to

• (L1)3] (comp3) catalysts allowed to show, on the one hand, the absence of solubility problems, and to discover, on the other hand, that the presence of three L1 ligands (comp3) leads to a reaction rate clearly lower than that of a catalyst carrying one or two ligands (see p. S7 of Supporting

• Information File 1 for the reaction kinetic curves of catalysts). In addition, the catalyst with a single L1 ligand (comp1) was found to be more reactive than the one with two ligands (comp2), and was therefore selected for further optimization. In contrast, comparison of its reaction kinetic curve with that

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

• ) and carbon–heteroatom (C–X) bonds has been and still is a central topic in organic synthesis [1][2]. Historically, organic chemists have extensively relied on the use of noble-metal-based catalysts (e.g., Pd, Rh, Ir, among others) to achieve such type of functionalization [3][4][5]. However, reliance

Transition-metal-catalyzed domino reactions of strained bicyclic alkenes

• Austin Pounder,
• Eric Neufeld,
• Peter Myler and
• William Tam

Beilstein J. Org. Chem. 2023, 19, 487–540, doi:10.3762/bjoc.19.38

• reaction conditions, without adding additional reagents and catalysts, and in which the subsequent reactions result as a consequence of the functionality formed in previous steps [1]. Bicyclic alkenes, a family of strained ring systems, have seen widespread applications in organic synthesis in the last 20

• -defined and rigid nature of these bicyclic alkenes creates two diastereotopic faces, namely the endo and exo face (Figure 2). The exo face is sterically less congested than the endo face; therefore, the exo face will typically interact with metal catalysts through side-on coordination of the olefin, and

• metal catalysts towards coordination on the exo face biases the reaction outcome towards exo-selective functionalization. Upon exo coordination of a metal catalyst with the π system and subsequent migratory insertion, the resulting alkyl metal intermediate is quite limited in how it can propagate. In

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

• polysubstituted derivative 21g was also functionalized in high yield (71%). Pleasingly, other metals have been also successfully applied for the trifluoromethylthiolation of aromatic derivatives by C(sp2)–H bond activation such as Rh(III) and Co(III)-based catalysts as depicted below. Rhodium catalysis: In 2015

• catalysts for such functionalization. In 2013, the group of Daugulis described the copper-catalyzed ortho-2,2,2-trifluoroethoxylation of a 3-trifluoromethylated benzamide derived from 8-aminoquinoline, giving the corresponding product in 73% yield [149]. The group of Baidya showed that the dehydrogenative

Mechanochemical solid state synthesis of copper(I)/NHC complexes with K₃PO₄

• Ina Remy-Speckmann,
• Birte M. Zimmermann,
• Mahadeb Gorai,
• Martin Lerch and
• Johannes F. Teichert

Beilstein J. Org. Chem. 2023, 19, 440–447, doi:10.3762/bjoc.19.34

• focus has seldomly been on the preparative methods to access the required catalysts themselves. As case in point, we decided to re-investigate the synthesis of copper(I)/N-heterocyclic carbene (NHC) complexes, which are broadly applicable catalysts for a wide variety of transformations [4][5][6]. While

• to the wide area of applications of mechanochemical synthesis but also showcase that transition metal complexes bearing additional functional groups can be prepared with a ball milling synthesis. We think that our protocol could be useful for the atom economic preparation of other complex catalysts

Combretastatins D series and analogues: from isolation, synthetic challenges and biological activities

• Jorge de Lima Neto and
• Paulo Henrique Menezes

Beilstein J. Org. Chem. 2023, 19, 399–427, doi:10.3762/bjoc.19.31

• catalysts, through dimerization of a single molecule. Pettit and co-workers investigated the influence of structural modifications on the biological activity of combretastatins D-2 (2) and D-4 (4). The authors also investigated the influence of solvents and functional groups in the total synthesis of the

CuAAC-inspired synthesis of 1,2,3-triazole-bridged porphyrin conjugates: an overview

• Dileep Kumar Singh

Beilstein J. Org. Chem. 2023, 19, 349–379, doi:10.3762/bjoc.19.29

• . Since all of the triazole-linked porphyrins discussed in this review were prepared for different applications, most of the discussion focuses on the clicked synthetic parts under different reaction conditions that include different Cu catalysts, solvent systems, ligands, and temperatures. Most of the

• than other copper catalysts, as it provided higher yields of the desired products (Scheme 4). In 2010, Shetti and Ravikanth [28] nicely utilized the "click reaction" approach for the preparation of a series of triazole-bridged porphyrin-ferrocene dyads 37a–d in 48–52% yield by the reaction between two

• copper catalysts have been used for the CuAAC-based synthesis of these porphyrin conjugates, the majority of the reports using CuSO4 with either ascorbic acid or sodium ascorbate, and Cu(OAc)2 with sodium ascorbate under an organic solvent or a mixture of organic solvents and water. In addition, other Cu

Group 13 exchange and transborylation in catalysis

• Dominic R. Willcox and
• Stephen P. Thomas

Beilstein J. Org. Chem. 2023, 19, 325–348, doi:10.3762/bjoc.19.28

• review will explore the use of group 13 exchange reactions as a general method for catalytic turnover, and serves to expand on the previously published review on transborylation-enabled boron catalysis to include a broader range of catalysts and turnover reagents [47]. Review Boron catalysis The borane

• -trifluorophenyl)borane [54], BH3 [55][56][57], and H-B-9-BBN [58] have also been reported as catalysts for the hydroboration of alkynes with HBpin (Scheme 2). Lloyd-Jones et al. investigated the mechanism of this reaction and found transborylation, group 13 exchange between boron atoms, enabled catalytic turnover

• tris[3,5-bis(trifluoromethyl)phenyl]borane [59], tris(3,4,5-trifluorophenyl)borane [54], and BH3 [55][56] found to be competent catalysts of this transformation (Scheme 3a). The mechanism was proposed to be analogous to that of borane-catalysed alkyne hydroboration; alkene 4 hydroboration, followed by

Strategies to access the [5-8] bicyclic core encountered in the sesquiterpene, diterpene and sesterterpene series

• Cécile Alleman,
• Charlène Gadais,
• Laurent Legentil and
• François-Hugues Porée

Beilstein J. Org. Chem. 2023, 19, 245–281, doi:10.3762/bjoc.19.23

• ][9]. Metathesis reactions take place by the means of a metallic catalyst. Firstly, olefin metathesis was achieved with an air-sensitive tungsten complex [8]. An important focus on air-stable catalyst design was undertaken and contributed to the popularization of the reaction. Thus, Grubbs catalysts

• of 1st and 2nd generation (G-I and G-II, respectively) as well as more recent Hoveyda–Grubbs 1st or 2nd generation (HG-I and HG-II, respectively) (Figure 2) are now commercially available. Today, the design of new efficient catalysts is at the heart of research [4][5][6][7][9][10][11][12]. The

• from 2 equivalents of 99 and the cross metathesis adduct resulting from 99 and a styrene unit coming from the catalyst. In addition, the corresponding RCM on the alkene analogue of 99 did not proceed either with G-II or Schrock catalysts, showcasing the substrate sensitivity of this reaction. 1.3