Synthesis, liquid crystalline behaviour and structure–property relationships of 1,3-bis(5-substituted-1,3,4-oxadiazol-2-yl)benzenes

• Afef Mabrouki,
• Malek Fouzai,
• Armand Soldera,
• Abdelkader Kriaa and
• Ahmed Hedhli

Beilstein J. Org. Chem. 2020, 16, 149–158, doi:10.3762/bjoc.16.17

• electron D–A concept may be regarded as Lewis base–Lewis acid type or charge-transfer. Based upon the above considerations, we could attribute the close proximity of fluorinated chains in conformation B to a throw space electron D–A intramolecular interaction between the perfluoroalkyl chains (electron

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

• Katarzyna Włodarczyk,
• Piotr Borowski and
• Marek Stankevič

Beilstein J. Org. Chem. 2020, 16, 88–105, doi:10.3762/bjoc.16.11

• reaction. In the presence of a Brønsted acid, mainly [1,3]-rearrangement is observed, whereas a Lewis acid catalyzes the [1,4]-sulfur migration. To gain insight into the mechanism of these transformations, the stereochemistry of these rearrangements have been tested, along with the conduction of some

• remains to be proved for Lewis acid use. It was then decided to prepare substrates possessing double bonds at the β position (Scheme 6). It appeared that the sulfides derived from aldehydes 8 and 9 failed to undergo transformation to the corresponding alkenylphosphine sulfides when treated with a MsCl

• 2 and 3). The difference must therefore have arisen from the different C–O bond dissociation energies of the alcohols and mesylates. Assuming that the Lewis acid coordinated to either hydroxy oxygen atom or to one of the oxygen atoms of the mesyl group, the activation energies for C–O bond

Synthesis of C-glycosyl phosphonate derivatives of 4-amino-4-deoxy-α-ʟ-arabinose

• Lukáš Kerner and
• Paul Kosma

Beilstein J. Org. Chem. 2020, 16, 9–14, doi:10.3762/bjoc.16.2

• preliminary experiments, Lewis acid cleavage using BBr3, BCl3, and TiCl4, respectively, was not successful, although the latter reagent had previously been used to deprotect two benzyl groups from an allyl glycoside containing a 4-amino-4-deoxy-ʟ-arabinose residue [36]. Cleavage of the benzyl protecting

Extension of the 5-alkynyluridine side chain via C–C-bond formation in modified organometallic nucleosides using the Nicholas reaction

• Renata Kaczmarek,
• Dariusz Korczyński,
• James R. Green and
• Roman Dembinski

Beilstein J. Org. Chem. 2020, 16, 1–8, doi:10.3762/bjoc.16.1

• obtained successfully in moderate to good yields (Table 1). The reactions progressed quite slowly and required an excess amount of the Lewis acid (4–5 equiv) to proceed at a preparatively reasonable rate (Table 1, entries 1–4). These observations can be attributed to the substantial number of potentially

• nucleophile present was in slight excess relative to that of the Lewis acid, whereas limited amounts of nucleophile resulted in greater amounts of decomposition. Slightly more decomposition products were observed by TLC in reactions with ribo nucleoside 5 (Table 1, entries 4–7) than with 2'-deoxy derivative 4

SnCl₄-catalyzed solvent-free acetolysis of 2,7-anhydrosialic acid derivatives

• Kesatebrhan Haile Asressu and
• Cheng-Chung Wang

Beilstein J. Org. Chem. 2019, 15, 2990–2999, doi:10.3762/bjoc.15.295

• order to access glycans in a pure form. In line with this, various C-5-substituted 2,7-anhydrosialic acid derivatives bearing both electron-donating and -withdrawing protecting groups were synthesized and subjected to different Lewis acid-catalyzed solvent-free ring-opening reactions at room temperature

• -anhydro bridges [29][30][31]. Accordingly, ᴅ-galactosamine and ᴅ‑allosamine derivatives were synthesized via scandium(III) triflate-catalyzed ring opening of 1,6-anhydroglucosamine derivatives [29][32]. However, there is a paucity of reports on the Lewis acid-catalyzed acetolysis of the 2,7-anhydro

• the hydroxymethyl group in 10 to furnish 11 in 82% yield. After having obtained the 2,7-anhydrosialic acid derivatives 5–11, they were subjected to various Lewis acid-catalyzed ring-opening reactions. In line with this, Sc(OTf)3-, copper(II) triflate-, and SnCl4-catalyzed acetolysis of diacetylamino

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• chiral Co(II)-(R,R)salen complex 83 in DMF saturated with CO2 resulted in the formation of 84 in a low yield but with good enantioselectivity (Scheme 31). Very recently, Meggers research group described an application of an asymmetric Lewis acid catalyst using electricity to provide a synthetic route

• towards chiral 1,4-dicarbonyls bearing tertiary and all-carbon quaternary stereocenters via oxidative cross coupling of 2-acylimidazoles 85 with silyl enol ethers 86 (Scheme 32). Chiral Rh complex 87 was exploited as a Lewis acid catalyst for the purpose of activating the substrate towards anodic

• and his group developed an electrochemical strategy for the asymmetric alkylation of 2-acylimidazole derivatives 94 with substituted para-methylphenols 95 using Ni(OAc)2 as a Lewis acid catalyst in presence of chiral diamine ligand 96 (Scheme 34) [71]. Based on their detailed mechanistic studies, the

Self-assembled coordination thioether silver(I) macrocyclic complexes for homogeneous catalysis

• Zhen Cao,
• Aline Lacoudre,
• Cybille Rossy and
• Brigitte Bibal

Beilstein J. Org. Chem. 2019, 15, 2465–2472, doi:10.3762/bjoc.15.239

• ; homogeneous catalysis; prochiral; silver complex; thioether ligand; Introduction Since the early advances in the late eighties [1][2][3][4][5][6][7][8][9][10], silver(I) catalysis has been widely exploited based on the versatile redox and soft Lewis acid properties of this coinage metal cation. Silver

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

Friedel–Crafts approach to the one-pot synthesis of methoxy-substituted thioxanthylium salts

• Kenta Tanaka,
• Yuta Tanaka,
• Mami Kishimoto,
• Yujiro Hoshino and
• Kiyoshi Honda

Beilstein J. Org. Chem. 2019, 15, 2105–2112, doi:10.3762/bjoc.15.208

• presence of a Lewis acid such as SnCl4 and AlCl3 [12][13][14]. While these reactions were proven to be useful, they require the use of stoichiometric amounts of metals and/or toxic metal reagents. Moreover, there are only a few methods for the synthesis of thioxanthylium salts despite their useful active

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• , the trans-decalin scaffold is the ideal objective of numerous methodology studies. Inspired by nature’s highly efficient and stereochemically controlled syntheses of terpenes, up to now, various synthetic strategies to trans-decalin have been developed, e.g., Brønsted acid or Lewis acid-mediated

Application of chiral 2-isoxazoline for the synthesis of syn-1,3-diol analogs

• Juanjuan Feng,
• Tianyu Li,
• Jiaxin Zhang and
• Peng Jiao

Beilstein J. Org. Chem. 2019, 15, 1840–1847, doi:10.3762/bjoc.15.179

• the amount of the chiral Lewis acid catalyst led to a decrease of both the ee and the yield. Desilylation of the 2-isoxazolidine 1 was effected in CHCl3 using catalytic amounts of p-toluenesulfonic acid (PTSA). Though the yield of the in situ-generated 2-isoxazoline 2 bearing the 1,3-oxazolidin-2-one

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

• lithium enolate of methyl 4-methoxyphenylacetate would give the β-hydroxyester 169 which when treated with Lewis acid experienced the aziridine ring cleavage with simultaneous dihydrofuran-2-one ring closure to produce 170 contaminated with small amounts of the corresponding furan-2(5H)-one 171

• )-184 and its C4 epimer (2S,3R,4S,5R)-184 were accomplished from the aziridine aldehyde (2R,1'S)-6 (Scheme 49) [105]. The Lewis acid-catalyzed nucleophilic anti-addition of 2-trimethylsilyloxyfuran to (2R,1'S)-6 furnished diastereoisomerically pure secondary alcohol 185 since chelation-controlled

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• ][42][43][44]. Various copper salts have been used as Lewis acid in homogeneous catalysis. CuO nanoparticles (NPs) were used for C–N, C–S, C–O cross-coupling reactions and C-arylation. Recently, exploiting the cross-coupling tendency of CuO NPs, Reddy et al. have reported their use as a heterogeneous

• separation. This problem was resolved by the introduction of scandium triflate (Sc(OTf)3) as a promising reusable Lewis acid in Diels–Alder reactions by Kobayashi [78]. However, in recent years scandium(III) trifluoromethanesulfonate (Sc(OTf)3) has emerged as an efficient, mild, commercially available

• , inexpensive, water-tolerant Lewis acid catalyst in the formation of both carbon–carbon and carbon–heteroatom bonds, and thereby the formation of various biologically promising organic compounds [68]. Important advances in scandium-catalyzed chemistry include [4 + 2] and [2 + 2] cycloaddition reactions, Baeyer

Molecular basis for the plasticity of aromatic prenyltransferases in hapalindole biosynthesis

• Takayoshi Awakawa and
• Ikuro Abe

Beilstein J. Org. Chem. 2019, 15, 1545–1551, doi:10.3762/bjoc.15.157

• [13]. More interestingly, the D172A mutation altered the AmbP1 reaction, as it prefers C-3 prenylation even in the presence of Mg2+ ions. There are several X-ray crystal structural analyses of PTases that utilize Mg2+ as a Lewis acid, such as NphB [4], but this is the first structural analysis of the

Different reactivity of phosphorylallenes under the action of Brønsted or Lewis acids: a crucial role of involvement of the P=O group in intra- or intermolecular interactions at the formation of cationic intermediates

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1491–1504, doi:10.3762/bjoc.15.151

• phosphonic acids and other phosphorus-containing compounds. Contrary to Brønsted acids, 3-methylbuta-1,2-dien-1-ylphosphonic dichloride [Cl2(O=)P–HC=C=CMe2] reacted with the Lewis acid AlCl3 in an intermolecular way forming noncyclic intermediates, which were investigated by NMR spectroscopy and DFT

• such phosphorylallenes under the action of Brønsted or Lewis acids. Apart from that, the reaction of dichlorophosphorylallenes with arenes and AlCl3 led to products of hydroarylation of the allene system, phosphoryl-substituted alkenes and/or indanes. This is the first example of a Lewis acid-promoted

• substituents at the phosphorus atom of phosphorylallenes [13][14][15][16]. These cations were intermediates in Brønsted and Lewis acid-promoted intramolecular reactions of phosphorus-containing allenes with aromatic π-nucleophiles giving rise to various (bi)cyclic phosphorus-containing compounds [13][14][15

Mechanochemical Friedel–Crafts acylations

• Mateja Đud,
• Anamarija Briš,
• Iva Jušinski,
• Davor Gracin and
• Davor Margetić

Beilstein J. Org. Chem. 2019, 15, 1313–1320, doi:10.3762/bjoc.15.130

• ][31][32], also decreased yields (Table 1, entries 9 and 10). The reaction carried out in a planetary mill (Table 1, entry 11) afforded yields comparable to the MM400 vibrational mill. We have also performed screening of efficacy of various Lewis acid catalysts [33][34][35][36][37][38] (Table 1

Enantioselective Diels–Alder reaction of anthracene by chiral tritylium catalysis

• Qichao Zhang,
• Jian Lv and
• Sanzhong Luo

Beilstein J. Org. Chem. 2019, 15, 1304–1312, doi:10.3762/bjoc.15.129

• of a highly active carbocation Lewis acid catalyst. The stereocontrol potential of the chiral tritylium ion pair was demonstrated by its application in an enantioselective Diels–Alder reaction of anthracene. Keywords: anthracene; carbocation catalysis; Diels–Alder reaction; Fe(III)-based phosphate

• anion; tritylium salt; Introduction Carbocation Lewis acid catalysis has grown significantly over the last two decades [1][2][3][4][5][6][7][8][9][10][11][12][13]. The development of asymmetric carbocation catalysts has been long pursued but remains a challenging task. One strategy is to design and

• investigated in Lewis acid catalysis over the past decades, a chiral counter anion [34][35] with metal elements as the central atom, however, was seldom reported. Typically, the tritylium salts with weakly coordinating anions can be synthesized through a simple halide abstraction from the trityl halide in the

Steroid diversification by multicomponent reactions

• Leslie Reguera,
• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Daniel G. Rivera

Beilstein J. Org. Chem. 2019, 15, 1236–1256, doi:10.3762/bjoc.15.121

• of a Lewis acid like BF3·Et2O for a suitable activation of the imine. Based on the same idea of exploiting the reactivity of ynamides, Cui’s group developed a 3CR wherein an o-hydroxy-benzhydryl alcohol was used in place of the aldehyde or imine components upon reaction with ynamide and a carboxylic

• reaction reported in 1893 comprises the acid–catalyzed condensation of ethyl acetoacetate, benzaldehyde and urea to generate 3,4-dihydropyrimidin-2(1H)-one [41]. From that time, the reaction was extended to Lewis-acid catalysis and the use of other solvents such as methanol or aprotic solvents such as THF

Multicomponent reactions (MCRs): a useful access to the synthesis of benzo-fused γ-lactams

• Edorta Martínez de Marigorta,
• Jesús M. de Los Santos,
• Ana M. Ochoa de Retana,
• Javier Vicario and
• Francisco Palacios

Beilstein J. Org. Chem. 2019, 15, 1065–1085, doi:10.3762/bjoc.15.104

• -component reaction with aryldiazonium tetrafluoroborates 68, DABCO·(SO2)2 (69) and nitriles 70 under Ru(IV) photocatalysis with visible light and in the presence of a Lewis acid (Scheme 21) [101]. Up to 24 isoindolinone derivatives were obtained, bearing a wide variety of aryl moieties at the sulfonyl group

• -component reaction, to afford isoindolinones 53 substituted with nitrile or carboxamide groups (Scheme 15, method A) [93]. Trimethylsilylcyanide (52), and benzyl-, alkyl- and allylamines 2 were reacted with 2-formylbenzoic acid (33) in the presence of OSU-6, a mesoporous silica performing as a green Lewis

• acid catalyst for this transformation. At room temperature, the product of this environmentally friendly Strecker reaction is nitrile derivative 53 (R2 = CN, Scheme 15, method A), while at reflux carboxamide 53 (R2 = CONH2, Scheme 15, method A) is obtained. Notoriously, aromatic amines 2 did not work

A three-component, Zn(OTf)₂-mediated entry into trisubstituted 2-aminoimidazoles

• Alexei Lukin,
• Anna Bakholdina,
• Anna Kryukova,
• Alexander Sapegin and
• Mikhail Krasavin

Beilstein J. Org. Chem. 2019, 15, 1061–1064, doi:10.3762/bjoc.15.103

• propargylureas (leading to 2-imidazolones) and extend the range of Lewis acid-catalyzed azole syntheses based on N-carbonyl propargylamines. Keywords: alkyne hydroamination; cyclocondensation; Lewis acid catalysis; multicomponent reactions; propargylurea; Introduction The pioneering publications of Beller and

• turned our attention to propargylureas 4. These have been previously converted to the respective 2-imidazolones via base-promoted intramolecular amination of the propargyl group [5][6]. However, such transformations have not been studied under transition metal or Lewis acid catalysis. Moreover, the

Catalytic asymmetric oxo-Diels–Alder reactions with chiral atropisomeric biphenyl diols

• Chi-Tung Yeung,
• Wesley Ting Kwok Chan,
• Wai-Sum Lo,
• Ga-Lai Law and
• Wing-Tak Wong

Beilstein J. Org. Chem. 2019, 15, 955–962, doi:10.3762/bjoc.15.92

• reactions. Oxo-Diels–Alder (oxo-DA) reactions between electron-poor aldehydes and electron-rich dienes such as Danishefsky’s dienes or Brassard’s dienes are efficient ways to construct oxygen-containing six-membered heterocycles via [4 + 2] cyclizations, and have been dominated by metal-based chiral Lewis

• acid catalysts for over three decades [15][16][17][18][19][20][21][22][23][24][25][26]. Comparatively, interest in the utilization of metal-free organocatalytic oxo-DA reactions began to grow only after Rawal’s group reported a ground-breaking contribution in using a diol molecule, TADDOL, as a

Efficient synthesis of pyrazolopyridines containing a chromane backbone through domino reaction

• Razieh Navari,
• Saeed Balalaie,
• Saber Mehrparvar,
• Fatemeh Darvish,
• Frank Rominger,
• Fatima Hamdan and
• Sattar Mirzaie

Beilstein J. Org. Chem. 2019, 15, 874–880, doi:10.3762/bjoc.15.85

• products 5a–d were not formed. The reaction mechanism is shown in Scheme 2. The chemical structures of the products 5a–d are shown in Figure 4. Usually, to activate the nitrile group for cyclization reaction, the existence of Lewis acid, the addition of organolithium reagents or metal

Synthesis of acylglycerol derivatives by mechanochemistry

• Karen J. Ardila-Fierro,
• Andrij Pich,
• Marc Spehr,
• José G. Hernández and
• Carsten Bolm

Beilstein J. Org. Chem. 2019, 15, 811–817, doi:10.3762/bjoc.15.78

• stearic acid (3a) in the presence of amines such as pyridine or tributylamine. However, the analysis of the reaction mixture only showed unreacted starting materials. In previous work, an acceleration of the oxirane ring-opening reaction with carboxylic acids [34] or alcohols [35] by using Lewis acid

Catalyst-free assembly of giant tris(heteroaryl)methanes: synthesis of novel pharmacophoric triads and model sterically crowded tris(heteroaryl/aryl)methyl cation salts

• Rodrigo Abonia,
• Luisa F. Gutiérrez,
• Braulio Insuasty,
• Jairo Quiroga,
• Kenneth K. Laali,
• Chunqing Zhao,
• Gabriela L. Borosky,
• Samantha M. Horwitz and
• Scott D. Bunge

Beilstein J. Org. Chem. 2019, 15, 642–654, doi:10.3762/bjoc.15.60

• optimizing chemoselectivity. As a model reaction, an equimolar three-component mixture of precursors 1{1}, 6{2} and 7{1} was subjected to various catalyzed and uncatalyzed conditions and the results are summarized in Table 1. Further studies showed that the Lewis acid-catalyzed reactions (Table 1, entries 3

• at ambient temperature for 6 h until the starting materials 1 and 6 were no longer detected by TLC. The white precipitate formed was collected by filtration and washed with cold EtOH (2 × 0.5 mL). No further purification of product 8 was required. Alternatively, the more expensive Lewis acid Sc(OTf)3

Synthesis of the aglycon of scorzodihydrostilbenes B and D

• Katja Weimann and
• Manfred Braun

Beilstein J. Org. Chem. 2019, 15, 610–616, doi:10.3762/bjoc.15.56

• exclusively, so that, after cleavage of the ester groups, epi-scorzodihydrostilbene D (13) was obtained as single stereoisomer (Scheme 4). Obviously, the conditions required in the glycosylation reaction – excess of the Lewis acid and elongated reaction time – resulted in the formation of the

• -D-glucose pentaacetate in the presence of an excess of boron trifluoride etherate [20], a regioselective reaction occurred at the phenolic group in ortho-position to the alkyl side chain to give mono-glycosylated product 12. Chelation of the carbonyl and the neighboring phenolic group by the Lewis

• acid is assumed to be responsible for this regiochemical outcome. The 1H NMR spectrum of 12 clearly indicates – by the low-field shift of the phenolic hydrogen chelated with the carbonyl group – that glycosylation had not occurred at this position. Unfortunately, however, the α-anomer 12 formed