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

• their structural stability, flexibility, or complexing ability with transition metals [6][7][8][9][10][11][12]. meso-Aryl-substituted dipyrromethanes or tripyrranes are the most commonly used starting materials in hexaphyrin syntheses [13][14][15][16]. Osuka et al. made significant contributions to the

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

• utilities, there are still a few drawbacks associated with these photoredox reactions. One of the main limitations is the reliance on precious metals such as Ir, Ru, and Pd, or elaborate organic dyes that act as photosensitizers, which are either limited in abundance or require additional synthetic steps to

• 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

• light irradiation at either 440 nm or 456 nm, and they occurred in acetone at room temperature, without the need for transition metals or organic dyes as photosensitizers. Interestingly, it was discovered that solvation played a vital role in the overall process. These findings shed light on the

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

• ]. Among the most employed earth-abundant metal-based PS, Cu(I) complexes have the first place, not only in artificial photosynthesis, but also in a large variety of photo(redox)catalyses [12][13][14][15][16][17]. On the other hand, several complexes based on 3d transition metals, like manganese [18], iron

• [19][20][21], cobalt [22][23], and nickel [24][25], have been designed as CO2 reduction catalysts. This (supra)molecular approach is appealing for gaining a structure–property understanding with the goal of tunable and efficient activity. Among the 3d transition metals, cobalt is relatively abundant

Tying a knot between crown ethers and porphyrins

• Maksym Matviyishyn and
• Bartosz Szyszko

Beilstein J. Org. Chem. 2023, 19, 1630–1650, doi:10.3762/bjoc.19.120

• oligo(ethylene glycol) segment. These hybrid systems constitute a broad group of compounds, including crowned porphyrins, crownphyrins, and calixpyrrole-crown ether systems forming Pacman complexes with transition metals. Their unique nature accustoms them as excellent ligands and hosts capable of

• metals. In this perspective article, the overview of both the early designs of porphyrin-crown ether hybrids, as well as the most recent advances in the synthesis and characterisation of this remarkable group of macrocyclic systems, are addressed. The discussion covers the strategies employed in

• of the ring and incorporated entities, they can present relative rigidity or flexibility [17]. The adaptable molecules of crown ethers render them excellent hosts for a wide range of alkali- or alkaline earth metals and organic guests with which they typically interact through hydrogen bonding

C–H bond functionalization: recent discoveries and future directions

• Indranil Chatterjee

Beilstein J. Org. Chem. 2023, 19, 1568–1569, doi:10.3762/bjoc.19.114

• the abstraction of intramolecular hydrogen atoms. Radical chemistry is a viable alternative to the two-electron process, involving C–H bond functionalization in the absence of any ligand and using low-cost redox-active metals (Fe, Cu, Mn, etc.) rather than heavy metals (Rh, Ir, etc.). Although radical

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

• nitrite as a nitrogen-oxygen source, and solely using aluminum trichloride as the additive. This approach circumvents the need for costly or highly toxic transition metals and presents a novel pathway for the synthesis of isoxazole derivatives. Keywords: aluminum trichloride; Lewis acid; isoxazole

• derivatives; sodium nitrite; transition metals; Introduction The isoxazole derivatives not only exist in many natural products [1][2][3] and pharmaceutical intermediates [4][5][6][7], but also have great application values in organic synthesis [8][9] (Figure 1). In the past decades, many methods have been

• 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

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

• in DMF at 100 °C for 5 h [30]. We hypothesized that electron-withdrawing p-cyanophenyl azide 2b, would be better suited for optimizing the reaction conditions compared to the unsubstituted phenyl azide 2a. Taking a clue from the literature, we looked at transition metals that facilitate

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

• . A number of excellent reviews on different aspects of NHC chemistry has been published during this period [12][13][14]. NHCs have been widely employed in homogeneous catalysis [12] and as ligands for the preparation of coordination compounds of different metals [13]. The M–NHC bond is relatively

• (I) complexes are frequently used to prepare NHC complexes of late transition metals [37]. As mentioned earlier, Diez-González et al. prepared some NHC–Cu(I) complexes, such as 69 through transmetallation by reacting [(SIPr)AgCl] 68 with the corresponding copper salt at rt (Scheme 23). However

Organic thermally activated delayed fluorescence material with strained benzoguanidine donor

• Alexander C. Brannan,
• Elvie F. P. Beaumont,
• Nguyen Le Phuoc,
• George F. S. Whitehead,
• Mikko Linnolahti and
• Alexander S. Romanov

Beilstein J. Org. Chem. 2023, 19, 1289–1298, doi:10.3762/bjoc.19.95

• compete with classic phosphorescent emitters that employ scarce metals such as iridium and platinum [7][8][9]. Since its first report in 2012 by Uoyama et al., 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) has been a benchmark TADF emitter due to its high quantum yields and excellent

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

• interest in developing novel methodologies in this field of organic chemistry. Keywords: alkylation; cross-dehydrogenation coupling; ether; non-noble metals; Introduction Since the 1970s, organic chemists have developed many selective cross-coupling methods for the construction of C–C bonds, such as the

• 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

• . Route b: the α-C(sp3)–H bonds are activated by a combination of transition metals and radical initiators to give the alkyl radicals, which are coupled with other radical receptors to afford the target product. Cu-catalyzed reactions Copper (common oxidation states are +I, +II and +III) has a

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

• literature examples of nitrate oxidation of different transition metals, such as palladium. Control reactions further supported this proposal, including the inability of alternative Fe(III) salts (e.g., FeCl3) to form more than stoichiometric azide product in the absence of added nitrate. We believe this

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

• half potential (*E1/2 = −3.36 V vs SCE) even more negative than alkali metals including lithium, making it one of the most potent chemical reductants ever reported. Owing to this exceptional reductive redox power, hydrodehalogenation of various electron-poor and electron-rich aryl bromides and

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

• considerable attention by organic chemists because of the strategic importance of this process as well as the ability to synthesize functionalized aromatic molecules in a straightforward way. Many organic name reactions have been discovered utilizing the C–H bond functionalization concept [1]. Metals were

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

• including transition metals and rare earth metals has been described and some other organometallic systems also were shown to have catalytic reactivity. Adopting this catalytic reactivity of organometallics and also the special bidentate nature of phosphinoamide ligands, in 2021, Chen and group [58

• metals inhibits the metal–chiral ligand coordination, thus making the C–H alkylation of pyridine substrates challenging. In addition, transition-metal-catalyzed enantioselective C–H alkylation reactions of pyridine still remain a great challenge. In this regard, in 2022, Ye and co-workers [60] reported

• iridium catalysis was achieved by Shi [61] in 2010 through an unusual meta-selectivity for the first time (Scheme 11a). To achieve meta-selectivity, the group has screened various transition metals and revealed that a silyl-iridium complex promoted the addition of meta-pyridyl C–H bonds to aldehydes 50

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

• high potential for further optimization. Aerobic oxidation using transition metals instead of TEMPO was also investigated. Pd(OAc)2 (Table 1, entry 6) [42] and Cu(OAc)2 (Table 1, entry 7) [43], and Ni(OH)2 (Table 1, entry 8) [44] left the starting material 1a. Pd(OAc)2 led to moderate conversion, but

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

• all possess helpful and, to an extent, specific reactivity characteristics. Interesting boron and silicon enolates can be generated by asymmetric conjugate boration [16], or silylation [17]. From several potentially catalytically active transition metals, copper combines beneficial properties for both

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

• sketched in red, with newly formed cyclic structures being highlighted. Review Earth-abundant metals Among the transition metal used in organic synthesis, the late transition metals like rhodium, palladium, and iridium have taken center stage when it comes to methodology development. Although these late

• -stage transition metals have contributed immensely to synthetic organic and organometallic chemistry, increasing societal awareness in terms of sustainable developments and resource management has prompted chemists to explore the use of environmentally benign, inexpensive, and earth-abundant metals [18

• transition metals, this reaction proceeded smoothly with a broad range of ester-, ketone-, and amide-stabilized phosphorus ylides. Oxabenzonorbornadienes bearing both EWG and EDG substituents worked well including bridgehead-substituted substrates which only experienced a slight reduction in yield. Similar

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

• derivatives. Finally, the use of abundant non-noble transition metals [209][210][211] in such reactions combined or not with modern technologies (photocatalysis and electrocatalysis) is still underexplored and any advances will be of high importance especially from a sustainability point of view aiming at

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

• Dominic R. Willcox Stephen P. Thomas EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh, EH9 3FJ, United Kingdom 10.3762/bjoc.19.28 Abstract Catalysis is dominated by the use of rare and potentially toxic transition metals. The main group offers a potentially sustainable alternative

• reactivity to be rendered catalytic, and exhibit catalysis outwith Lewis acid-type activation. These exchange reactions have allowed redox-neutral catalysis complementary to and beyond the redox catalysis of the transition metals. Boron, aluminium, gallium, and indium have all been demonstrated in catalytic

Total synthesis of insect sex pheromones: recent improvements based on iron-mediated cross-coupling chemistry

• Eric Gayon,
• Guillaume Lefèvre,
• Olivier Guerret,
• Adrien Tintar and
• Pablo Chourreu

Beilstein J. Org. Chem. 2023, 19, 158–166, doi:10.3762/bjoc.19.15

• to overall processes with a low atom economy, generating a significant amount of chemical waste, and which can be expensive when noble metals such as palladium salts are required (Scheme 1). The high efficiency of transition-metal-catalyzed cross-coupling methods in C–C bond formation processes

• constitutes an extremely powerful tool in total synthesis. In order to reach sustainable and economically appealing conditions, the quest for the substitution of palladium by non-noble metals has been investigated for more than four decades. To address this issue, new eco-friendly synthetic routes relying on

Preparation of β-cyclodextrin/polysaccharide foams using saponin

• Max Petitjean and
• José Ramón Isasi

Beilstein J. Org. Chem. 2023, 19, 78–88, doi:10.3762/bjoc.19.7

• complexing with the PAH and having repulsive interactions with soil [21]. A large quantity of HOCs have been studied, such as naphthalene or fluoranthene [19]. The authors reported also the possibility of remediation of heavy metals by saponins [22]. Therefore, saponins are useful in soil washing

NaI/PPh₃-catalyzed visible-light-mediated decarboxylative radical cascade cyclization of N-arylacrylamides for the efficient synthesis of quaternary oxindoles

• Dan Liu,
• Yue Zhao and
• Frederic W. Patureau

Beilstein J. Org. Chem. 2023, 19, 57–65, doi:10.3762/bjoc.19.5

• advantage of circumventing the need for external redox additives and/or noble metals, using readily available and cost-effective NaI and PPh3 under mild reaction conditions. In a broader context, phosphine organocatalysis is probably still underappreciated in organic synthesis, and could lead to important

Two-step continuous-flow synthesis of 6-membered cyclic iodonium salts via anodic oxidation

• Julian Spils,
• Thomas Wirth and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2023, 19, 27–32, doi:10.3762/bjoc.19.2

• -established reagents for synthetic chemists. They are portrayed as an alternative to otherwise hazardous transition metals. This is due to their great reactivity in electrophilic group transfers [1][2][3][4], photo- or organocatalysis [5][6][7][8][9][10][11][12][13][14][15], and their utility as building

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

• /catalyst/byproduct to telescope several reactions before performing the final purification step offline (Scheme 8) [80][81][82][83]. Notable applications of metal scavengers such as QuadraPure® resins involve the removal of leached metals as well as catalytic amounts of homogeneous metal catalysts as

• reported by Pitts and collaborators. This study achieves full removal of metal species after common homogenous catalytic reactions such as a Suzuki–Miyaura reaction, Sonogashira reaction or hydrogenation mediated by Wilkinson’s catalyst [84]. Other interesting examples to remove transition metals in

• choice of suitable options. It is, however, anticipated that with the advent of more sophisticated and robust automation tools the field of flow chemistry will continue to embrace inline purification as a valuable approach to remove incompatible species for subsequent steps or scavenge precious metals or

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

• organic chemistry. It allows chemists to avoid the use of precious and (or) toxic metals by taking advantage of the catalytic activity of small and synthetically available molecules. Today, the term organocatalysis is mainly associated with redox-neutral asymmetric catalysis of C–C bond-forming processes

• fundamentally different mechanisms have been proposed for the oxidation of alcohols [96] (Scheme 12). When using transition metals such as Cu(I) as co-catalyst, both aminoxyl radicals and metal ions serve as one-electron oxidants in a joint two-electron oxidation. In this system, primary aliphatic alcohols can