Challenge N- versus O-six-membered annulation: FeCl₃-catalyzed synthesis of heterocyclic N,O-aminals

• Giacomo Mari,
• Lucia De Crescentini,
• Gianfranco Favi,
• Fabio Mantellini,
• Diego Olivieri and
• Stefania Santeusanio

Beilstein J. Org. Chem. 2024, 20, 1412–1420, doi:10.3762/bjoc.20.123

• goal, different Lewis acids (10 mol %) such as Zn(OTf)2, CuCl2, and FeCl3 were screened at room temperature in different solvents, employing compound 4a as the model substrate (Table 1). From the set of data collected, both the formation of N,O-aminal 5a and corresponding hemiaminal 6a were observed

Bismuth(III) triflate: an economical and environmentally friendly catalyst for the Nazarov reaction

• Manoel T. Rodrigues Jr.,
• Aline S. B. de Oliveira,
• Ralph C. Gomes,
• Amanda Soares Hirata,
• Lucas A. Zeoly,
• Hugo Santos,
• João Arantes,
• Catarina Sofia Mateus Reis-Silva,
• João Agostinho Machado-Neto,
• Leticia Veras Costa-Lotufo and
• Fernando Coelho

Beilstein J. Org. Chem. 2024, 20, 1167–1178, doi:10.3762/bjoc.20.99

• electrocyclization reaction could be mediated by weaker Lewis acids, and consequently a catalytic amount of them could be used. The first example of a catalytic version of the Nazarov cyclization was reported by Denmark and Jones [25][26][27][28][29][30][31]. They found that a substoichiometric amount of FeCl3 (40

• first asymmetric catalytic Nazarov reaction [32]. In recent years, several strategies were reported employing different Lewis acids, such as, AuCl3/AgSbF6, Cu(II), In(OTf)3, Ir(III), Al(III), Sc(OTf)3/LiClO4, In(OTf)3/diphenylphosphoric acid (DPP), Fe(OTf)3/(CF3)2PhB(OH)2, iodine [33][34][35][36][37][38

• ][39][40][41][42][43], and other strategies [44][45]. Although methodologies involving catalysis by Lewis acids are very efficient, including asymmetric versions of the Nazarov reaction, the experimental protocols are quite laborious in most cases, requiring low temperature, an inert atmosphere, or the

Advancements in hydrochlorination of alkenes

• Daniel S. Müller

Beilstein J. Org. Chem. 2024, 20, 787–814, doi:10.3762/bjoc.20.72

• a side note, it should be mentioned that Hutchings and colleagues reported the hydrochlorination of ethylene with Lewis acids on solid supports [52]. However, this work solely focuses on kinetic studies and is therefore not discussed in this report. Reactions with in situ-generated HCl HCl gas can

HPW-Catalyzed environmentally benign approach to imidazo[1,2-a]pyridines

• Luan A. Martinho and
• Carlos Kleber Z. Andrade

Beilstein J. Org. Chem. 2024, 20, 628–637, doi:10.3762/bjoc.20.55

• reactivity of the imine formation [24]. The most common catalysts are those derived from triflate salts such as Sc(OTf)3 [25], Yb(OTf)3 [26], In(OTf)3 [27] and Gd(OTf)3 [28], and inorganic Brønsted or Lewis acids like HClO4 [29], ZrCl4 [30], InCl3 [31], BiCl3 [32], RuCl3 [33], NH4Cl [34], HCl [35], LaCl3

Green and sustainable approaches for the Friedel–Crafts reaction between aldehydes and indoles

• Periklis X. Kolagkis,
• Eirini M. Galathri and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2024, 20, 379–426, doi:10.3762/bjoc.20.36

• -inflammatory, and even anticancer agents. Traditionally, the synthesis of BIMs has been achieved upon the acidic condensation of an aldehyde with indole, utilizing a variety of protic or Lewis acids. However, due to the increased environmental awareness of our society, the focus has shifted towards the

• or Lewis acids as catalysts. In 2010, Shiri published a review, where the majority of the acidic catalysts that have been employed for the synthesis of these compounds were presented [12]. Since then, various alternative acids have been applied including protic acids, such as silica-bonded S-sulfonic

• well as Lewis acids, such as FeCl3 [23][24], RuCl3·3H2O [25], AgNO3 [26], glycerol and [Fe(III)-(salen)]Cl [27], Fe(DS)3·nH2O [28], Sc(OTf)3 [29], B(C6F5)3 or PhSiCl3 [30] and Cp2TiCl2 [31]. However, most of these reactions face some serious drawbacks, such as the requirement of large quantities of the

Mechanisms for radical reactions initiating from N-hydroxyphthalimide esters

• Carlos R. Azpilcueta-Nicolas and
• Jean-Philip Lumb

Beilstein J. Org. Chem. 2024, 20, 346–378, doi:10.3762/bjoc.20.35

• electrochemical conditions and can be influenced by a number of factors, including the nature of the electron donor, the use of Brønsted and Lewis acids, and the possibility of forming charge-transfer complexes. Such versatility creates many opportunities to influence the reaction conditions, providing a number

• transfer complexes with a donor species 6 or via LUMO lowering activation with Brønsted and Lewis acids 7 (Scheme 2B), collectively offering a number of variables to influence their reactivity. Upon reduction, RAEs give rise to a radical anion 8 with a weakened N–O bond (BDE < 70 kcal/mol) [33]. While

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

• ], 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

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

• ). When 5 equiv sodium nitrite were used, the corresponding yield was also decreased (Table 1, entry 4). Other Lewis acids employed in the reaction were less effective than AlCl3 (Table 1, entries 5–7). Furthermore, solvent screening showed that DMAc was the best reaction medium for this cycloaddition

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

• imidated product 32. In 2018, an Fe-catalyzed carbosulfenylation and carboselenylation 33 of alkenes with N-(thio/seleno)phthalimides 14 was introduced by Lv and Li (Scheme 17) [54]. The use of Lewis acids, such as AlCl3, ZnCl2, InCl3, Fe(OTf)2 and Fe(acac)3 was not beneficial. However, BF3·OEt2, SnCl4

Cyclization of 1-aryl-4,4,4-trichlorobut-2-en-1-ones into 3-trichloromethylindan-1-ones in triflic acid

• Vladislav A. Sokolov,
• Andrei A. Golushko,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2023, 19, 1460–1470, doi:10.3762/bjoc.19.105

• ; indanones; trichloromethyl group; triflic acid; Introduction Superelectrophilic activation of organic compounds under the action of strong Brønsted and Lewis acids is an effective method for the synthesis of various carbocycles and heterocycles, and polyfunctional compounds (see books [1][2] and reviews [3

• ][4][5][6][7][8][9][10]). Protonation (or coordination) of basic centers (carbons of unsaturated bonds and heteroatoms) of organic molecules in Brønsted (or Lewis) acids gives rise to not only monocations, but also to highly reactive dicationic (and even higher charged) species. Thus, different

• Brønsted and Lewis acids were also tested for this cyclization. Thus, enones 2a and 2e were not transformed into the corresponding indanones 3 in neat sulfuric acid (H2SO4) at room temperature for 3 days. That is in accord with literature data [19], where H2SO4 was used for dehydration of hydroxy ketones 1

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

• properties of transition metals and Lewis acids [69][70][71][72]. These advantages make iron salts attractive catalysts or reagents in chemical transformations and are considered ideal materials for developing catalysts [73]. Fe-catalyzed CDC reactions have achieved remarkable achievements in recent years

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

• 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

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

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

• conditions (Scheme 10). Green chemistry approach for the Clauson–Kaas synthesis of N-substituted pyrroles This section describes the Clauson-Kaas pyrrole syntheses using different greener methods in the presence of various Brønsted acids or Lewis acids. These include reactions in aqueous media, under solvent

• -catalyzed reactions under heating conditions. However, due to environmental concerns, the second part of this review focuses on greener Clauson–Kaas reaction protocols. Various Brønsted acids, Lewis acids, transition metal catalysts, and organocatalysts have been used in water as a green solvent, under

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

• . In addition, the lone pair electrons of the nitrogen atom interact with Lewis acids instead of the π-electrons of the ring system thus resulting to its reduced reactivity for electrophilic aromatic substitution reactions, such as a Friedel–Crafts reaction [21][22][23]. Hence, it is challenging to

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

• building blocks providing an aminomethyl moiety upon adding nucleophiles. Protected formaldehyde aminals are useful synthetic equivalents to formaldehyde imines. The imine functionality can be unmasked (68) in the reaction medium by Lewis acids such as TiCl4. The formed Mg enolates 66 readily react with

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

• in catalysis beyond their typical use as Lewis acids [46]. This strategy has allowed the synthesis of bench-stable boronic ester products, rather than sensitive alkylboranes, and enabled the use of substoichiometric amounts of enantioenriched boron reagents, which can be challenging to prepare. This

Friedel–Crafts acylation of benzene derivatives in tunable aryl alkyl ionic liquids (TAAILs)

• Swantje Lerch,
• Stefan Fritsch and
• Thomas Strassner

Beilstein J. Org. Chem. 2023, 19, 212–216, doi:10.3762/bjoc.19.20

• the different Lewis acids, the reaction is regioselective for the para-position. TAAIL 6 was chosen for further optimizations because it appeared to be a slightly better reaction medium compared to the other TAAILs. To optimize the yield of the reaction and to reduce the reaction time, different

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

• , entry 4). The scope of the reaction with 3,4-dihydroisoquinoline substrates as cyclic imines was investigated under these conditions [35]. In the current work, we first opted to examine the activities of other Lewis acids in the aza-Nazarov cyclization of imine 5a with acyl chloride 6b. The reason of

• , screening a variety of conditions including the use of stoichiometric and substoichiometric amounts of Lewis acids such as AgOTf and BF3·OEt2 with and without heating (23 and 80 °C) did not afford any targeted aza-Nazarov product 30 (for details see Table S1 in Supporting Information File 1). The reactivity

• aforementioned formation of the hydrolysis side product 34 support pathway I, we sought to design an experiment to rule out pathway II. To this end, we investigated the potential reaction between imine 5a and α,β-unsaturated ester 36 in the presence of a variety of Lewis acids (Scheme 8b). The reason of using

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

• ]. 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

Vicinal ketoesters – key intermediates in the total synthesis of natural products

• Marc Paul Beller and
• Ulrich Koert

Beilstein J. Org. Chem. 2022, 18, 1236–1248, doi:10.3762/bjoc.18.129

• intramolecular aldol addition of ketones such as 7 (Scheme 2) [5]. Brønsted-acid catalysis leads via a transition state 8 to the aldol 9, while the use of chelating Lewis acids results via 10 in the epimeric aldol 11. This review is a collection of total syntheses of natural products where vicinal keto esters

Reductive opening of a cyclopropane ring in the Ni(II) coordination environment: a route to functionalized dehydroalanine and cysteine derivatives

• Oleg A. Levitskiy,
• Olga I. Aglamazova,
• Yuri K. Grishin and
• Tatiana V. Magdesieva

Beilstein J. Org. Chem. 2022, 18, 1166–1176, doi:10.3762/bjoc.18.121

• in the side chain; the regioselectivity can be tuned by the addition of Lewis acids. This type of non-proteinogenic amino acid derivatives is not easily available but strongly required due to their bioactivity. One-pot nucleophilic in situ functionalization of the double bond of dehydroalanine

• radical anions influenced by substituents in the cyclopropane ring are discussed. Optimization of the reaction conditions opens a route to the non-proteinogenic amino acid derivatives containing an α–β or β–γ double C=C bond in the side chain; the regioselectivity can be tuned by the addition of Lewis

• acids. One-pot combination of the reductive ring opening and subsequent addition of thiols allows obtaining the cysteine derivatives in practical yields and with high stereoselectivity at the removed β-stereocenter. Keywords: amino acids; cathodic cyclopropane opening; cysteine derivatives; Ni–Schiff

Post-synthesis from Lewis acid–base interaction: an alternative way to generate light and harvest triplet excitons

• Hengjia Liu and
• Guohua Xie

Beilstein J. Org. Chem. 2022, 18, 825–836, doi:10.3762/bjoc.18.83

• materials with the introduction of Lewis acids have been frequently observed due to either physical or chemical interactions. In this mini-review, we elaborate how Lewis acids adjust the optical properties and the bandgap of luminescent materials by simple coordination reactions. It is common that

• fluorescent materials containing Lewis basic nitrogen heterocycles are more likely to provide the feasible band gap modulation. The essence of such phenomenon originates from Lewis acid–base coordination and adducts, which highly depends on the electron-accepting property of the Lewis acids. This

• emitters can be realized by adding a Lewis acid to a fluorescent conjugated compound [15][16]. Lewis acids are common complexing agents [17] and are frequently used to dope conjugated polymers to enhance their conductivity while the luminescence is completely quenched [18][19]. In contrast, in the presence

A trustworthy mechanochemical route to isocyanides

• Francesco Basoccu,
• Federico Cuccu,
• Federico Casti,
• Rita Mocci,
• Claudia Fattuoni and
• Andrea Porcheddu

Beilstein J. Org. Chem. 2022, 18, 732–737, doi:10.3762/bjoc.18.73

• (GC–MS analysis). Unexpectedly, the addition of Lewis acids, namely LiCl and BF3·Et2O, did not improve the enolate generation. The next step was searching the optimal conditions for a better conversion of 1f in 2f. These were found in the 1:2:7 ratios of the three components with the addition of 400

Menadione: a platform and a target to valuable compounds synthesis

• Acácio S. de Souza,
• Ruan Carlos B. Ribeiro,
• Dora C. S. Costa,
• Fernanda P. Pauli,
• David R. Pinho,
• Matheus G. de Moraes,
• Fernando de C. da Silva,
• Luana da S. M. Forezi and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 381–419, doi:10.3762/bjoc.18.43

• an equimolar ratio of 500 mM, the Diels–Alder reaction achieved 98% and 2% recovery of starting material after 72 h, at an estimated product generation rate of 142.5 μM/h. In this context, it was possible to apply a green methodology without the application of heating or the use of Lewis acids

• , contributing significantly to the progress of the synthesis studies in aqueous medium. The Diels–Alder reaction using menadione (10) was also studied by Bendiabdellah and co-workers, who reported the intramolecular Diels–Alder domino reactions promoted by Lewis acids [110]. The reaction involving menadione (10

• dithionite, followed by hydroacetylation of 14 with acetic anhydride, using nanoscopic acidic hydroxylated metal fluorides MFn-x(OH)x (M = Mg, Al; n = 2, 3; x < 0.1) as catalysts. This type of catalysts has a huge acidic versatility, once they can behave as Brønsted or Lewis acids. The reductive acetylation