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

A resorcin[4]arene hexameric capsule as a supramolecular catalyst in elimination and isomerization reactions

• Tommaso Lorenzetto,
• Fabrizio Fabris and
• Alessandro Scarso

Beilstein J. Org. Chem. 2022, 18, 337–349, doi:10.3762/bjoc.18.38

• compared to many other strong Brønsted or Lewis acids. Keywords: cationic intermediates; encapsulation; organocatalysis; resorcin[4]arene hexamer; supramolecular catalysis; Introduction In enzymatic catalysis, the substrate is selected matching the size, shape and specific functional groups present in

• , isolated from oils distilled from citronella plants, which is very effective as a repellent and antifungal. In the presence of Brønsted or Lewis acids (S)-citronellal undergoes an intramolecular carbonyl–ene cyclization reaction forming two new stereogenic centers, which turns out into four possible

• protonation occurred preferentially on the alkene moiety. It is worth to note that the present dehydration reaction of 1,1-diphenylethanol with 16 occurs under mild experimental conditions with respect to recent examples in the literature operating with strong Brønsted and Lewis acids like sulfuric acid [57

Green synthesis of C5–C6-unsubstituted 1,4-DHP scaffolds using an efficient Ni–chitosan nanocatalyst under ultrasonic conditions

• Soumyadip Basu,
• Sauvik Chatterjee,
• Suman Ray,
• Suvendu Maity,
• Prasanta Ghosh,
• Asim Bhaumik and
• Chhanda Mukhopadhyay

Beilstein J. Org. Chem. 2022, 18, 133–142, doi:10.3762/bjoc.18.14

• varied the reaction time, it was found that the highest yield was achieved with 15 minutes of ultrasonic irradiation (Table 2, entry 10). The use of chitosan (Table 2, entry 12) as a catalyst resulted only in traces of the product. We also used various Lewis acids, such as NiCl2, ZnCl2, and FeCl3 (Table

•  2, entries 13–15). A moderate to low yield was obtained when using these Lewis acids. To identify the optimal quantity of the catalyst, we altered the amount in several model reactions. It was found that the highest yield was obtained when 30 mg of the catalyst was used (Table 2, entry 17), and

Me₃Al-mediated domino nucleophilic addition/intramolecular cyclisation of 2-(2-oxo-2-phenylethyl)benzonitriles with amines; a convenient approach for the synthesis of substituted 1-aminoisoquinolines

• Krishna M. S. Adusumalli,
• Lakshmi N. S. Konidena,
• Hima B. Gandham,
• Krishnaiah Kumari,
• Krishna R. Valluru,
• Satya K. R. Nidasanametla,
• Venkateswara R. Battula and
• Hari K. Namballa

Beilstein J. Org. Chem. 2021, 17, 2765–2772, doi:10.3762/bjoc.17.186

• appropriate ester of benzoic acid in the presence of a base. After having the starting material in hand, we commenced our investigations for the synthesis of 1-aminoisoquinolines by treating 2-(2-oxo-2-phenylethyl)benzonitrile (3a) with aniline (4a) in the presence of different Lewis acids under varying

Synthetic strategies toward 1,3-oxathiolane nucleoside analogues

• Umesh P. Aher,
• Dhananjai Srivastava,
• Girij P. Singh and
• Jayashree B. S

Beilstein J. Org. Chem. 2021, 17, 2680–2715, doi:10.3762/bjoc.17.182

• -oxathiolane nucleosides via resolution methods. The chemical as well as enzymatic procedures are reviewed and segregated in this review for effective synthesis of 1,3-oxathiolane nucleoside analogues. Keywords: chiral auxiliaries; enzymes; Lewis acids; N-glycosylation; 1,3-oxathiolane sugar and nucleosides

• ]. Appropriate Lewis acids form a complex with the oxathiolane intermediates via in situ chelation. The exclusive formation of the β-anomer was observed upon coupling of the anomer mixture 8 with silylated cytosine using stannic chloride (about 2 equiv in CH2Cl2 at room temperature). This stereoselective outcome

AlBr₃-Promoted stereoselective anti-hydroarylation of the acetylene bond in 3-arylpropynenitriles by electron-rich arenes: synthesis of 3,3-diarylpropenenitriles

• Yelizaveta Gorbunova,
• Dmitry S. Ryabukhin and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2021, 17, 2663–2667, doi:10.3762/bjoc.17.180

• arenes under the action of the strong Lewis acids, aluminum halogenides AlX3 (X = Cl, Br) and the Brønsted superacid TfOH (CF3SO3H). Results and Discussion It was found that acetylene nitriles 1a–c reacted with arenes in the presence of excess AlBr3 (6 equiv) at room temperature for 0.5–2 h to afford E,Z

Synthesis of new bile acid-fused tetrazoles using the Schmidt reaction

• Dušan Đ. Škorić,
• Olivera R. Klisurić,
• Dimitar S. Jakimov,
• Marija N. Sakač and
• János J. Csanádi

Beilstein J. Org. Chem. 2021, 17, 2611–2620, doi:10.3762/bjoc.17.174

• if the excess of hydrazoic acid is present, tetrazole can be formed as an alternative product. It is established that the use of nonaqueous conditions and concentrated mineral acids or Lewis acids favors the second pathway [22], and thus increasing the possibility of tetrazole formation

α-Ketol and α-iminol rearrangements in synthetic organic and biosynthetic reactions

• Scott Benz and
• Andrew S. Murkin

Beilstein J. Org. Chem. 2021, 17, 2570–2584, doi:10.3762/bjoc.17.172

• later explored alternative Brønsted and Lewis acids that could effectively catalyze the rearrangement of symmetric α‑hydroxy aldimines [29]. A catalyst screen was performed on the model substrate 97a (97 with R = Ph; Figure 19a) using three different Brønsted acids (acetic acid, sulfuric acid, and p

• -toluenesulfonic acid), five different Lewis acids (Zn(OTf)2, Cu(OTf)2, Sc(OTf)2, silica gel, and montmorillonite K 10), and one base (NaOEt). Of these, silica gel and montmorillonite K 10 had the best yields (95% and 100%, respectively). A substrate scope was then determined for 97 using aryl, n-hexyl, and

• rearrangements catalyzed by silica gel and montmorillonite K 10. a) For 102a (102 with R = Ph), silica gel and montmorillonite K 10 gave ≥95% yields, while Brønsted acids, other Lewis acids, and NaOEt generally performed much more poorly. b) Electron-rich R groups rearrange efficiently in the presence of silica

Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones

• Robin Klintworth,
• Garreth L. Morgans,
• Stefania M. Scalzullo,
• Charles B. de Koning,
• Willem A. L. van Otterlo and
• Joseph P. Michael

Beilstein J. Org. Chem. 2021, 17, 2543–2552, doi:10.3762/bjoc.17.170

• 15a was heated in capped tubes under microwave conditions [35][36][37] for 10 minutes in solvents such as ethanol (100 °C), xylene (150 °C) or N,N-dimethylformamide (150 °C) (Table 1, entries 3–5). Dissolution in neat protic or Lewis acids (e.g., hydrochloric acid, trifluoroacetic acid

Direct C(sp³)–H allylation of 2-alkylpyridines with Morita–Baylis–Hillman carbonates via a tandem nucleophilic substitution/aza-Cope rearrangement

• Siyu Wang,
• Lianyou Zheng,
• Shutao Wang,
• Shulin Ning,
• Zhuoqi Zhang and
• Jinbao Xiang

Beilstein J. Org. Chem. 2021, 17, 2505–2510, doi:10.3762/bjoc.17.167

• allylic functionalization of 2-alkylazaarenes. Due to the high pKa value of alkyl azaarenes, the functionalization of benzylic C(sp3)–H was challengeable and pre-activation of the benzylic proton with suitable Lewis acids was often required prior to deprotonation of the alkyl chain by a stoichiometric

Copper-catalyzed monoselective C–H amination of ferrocenes with alkylamines

• Zhen-Sheng Jia,
• Qiang Yue,
• Ya Li,
• Xue-Tao Xu,
• Kun Zhang and
• Bing-Feng Shi

Beilstein J. Org. Chem. 2021, 17, 2488–2495, doi:10.3762/bjoc.17.165

• development of efficient methods to access multifunctional ferrocenes has attracted tremendous attention. Conventionally, functionalized ferrocenes were derived via electrophilic aromatic substitution mediated by strong Lewis acids or direct metalation using strong bases, such as alkyllithium reagents [3][9

Synthesis of 5-arylacetylenyl-1,2,4-oxadiazoles and their transformations under superelectrophilic activation conditions

• Andrey I. Puzanov,
• Dmitry S. Ryabukhin,
• Anna S. Zalivatskaya,
• Dmitriy N. Zakusilo,
• Darya S. Mikson,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2021, 17, 2417–2424, doi:10.3762/bjoc.17.158

• (TfOH), the strong Lewis acids AlX3 (X = Cl, Br), or the acidic zeolite CBV-720. Results and Discussion The synthesis of 5-arylethynyl-1,2,4-oxadiazoles 3 was based on transformations of the corresponding 5-styryloxadiazoles, i.e., 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles 1a–g (Scheme 1). Bromination

• proton and aromatic protons (see Supporting Information File 1). In the case of the reaction with o-xylene, pairs of E/Z-isomers of two regioisomers, (E/Z)-5b and (E/Z)-5b1, were obtained. We also checked the reaction of oxadiazole 3a with benzene under the action of Lewis acids AlCl3, AlBr3 and acidic

• zeolite CBV-720 (Table 2). However, these Lewis acids showed unsatisfactory results leading to oligomeric materials (Table 2, entries 1 and 2). Probably, due to some secondary reactions of the formed compound 5a with AlCl3, AlBr3. The yield of target compound 5a in the reaction with zeolite was lower than

Advances in mercury(II)-salt-mediated cyclization reactions of unsaturated bonds

• Sumana Mandal,
• Raju D. Chaudhari and
• Goutam Biswas

Beilstein J. Org. Chem. 2021, 17, 2348–2376, doi:10.3762/bjoc.17.153

• establishing this fact [26][27][28][29]. However, the main drawback of Hg(II) salts, as compared to other transition metal salts, is their increased toxicity [30][31]. Hg(II) salts on the other hand, are very cheap in comparison to other transition metal salts (Table 1) and one of the soft Lewis acids of the

Photoredox catalysis in nickel-catalyzed C–H functionalization

• Lusina Mantry,
• Rajaram Maayuri,
• Vikash Kumar and
• Parthasarathy Gandeepan

Beilstein J. Org. Chem. 2021, 17, 2209–2259, doi:10.3762/bjoc.17.143

• deactivates the other hydridic bonds such as α-amino and α-oxy C‒H bonds. Among the tested 24 Lewis acids, the zinc salts (ZnCl2 and ZnBr2) gave the best results. The method's potency was further shown by the synthesis of the drug fluoxetine (21) in three steps (Scheme 12) [63]. The transformation was