A selective removal of the secondary hydroxy group from ortho-dithioacetal-substituted diarylmethanols

• Anna Czarnecka,
• Emilia Kowalska,
• Agnieszka Bodzioch,
• Joanna Skalik,
• Marek Koprowski,
• Krzysztof Owsianik and
• Piotr Bałczewski

Beilstein J. Org. Chem. 2018, 14, 1229–1237, doi:10.3762/bjoc.14.105

• diarylmethyl alcohols with hydride sources. These reactions require a preliminary C–OH bond activation by Brønsted or Lewis acids. Several reagent systems have recently been employed to achieve this goal, including: NaBH4–CF3COOH [26], ZnI2–NaBH3CN [27], HI–Pred [28], H3PO2–I2 [29][30], Mo(CO)6-Lawesson’s

• reagent [31], PBr3 [32], BF3·Et2O–dibutyl ether [33] and silanes (Si–H) in the presence of various Lewis acids: B(C6F5)3 [34][35][36], InCl3 [37][38], H3[PW12O40]×nH2O [39], Ca(NTf2)2 [40], Bi(OTf)3 [41], Sn(IV)-montmorillonite [42] and PdCl2 [43]. It is interesting that Seto et al. reported that Et3SiH

• of alcohols by Brønsted or Lewis acids. Therefore, diarylmethanols bearing electron-donating substituents (EDG = methyl, methoxy) are reduced much faster than diarylmethanols with electron-withdrawing groups (EWG = CF3, C(O)OR) on (hetero)aryl moieties. Consequently, dramatically decreased yields

Hypervalent iodine-guided electrophilic substitution: para-selective substitution across aryl iodonium compounds with benzyl groups

• Cyrus Mowdawalla,
• Faiz Ahmed,
• Tian Li,
• Kiet Pham,
• Loma Dave,
• Grace Kim and
• I. F. Dempsey Hyatt

Beilstein J. Org. Chem. 2018, 14, 1039–1045, doi:10.3762/bjoc.14.91

• ), product yields and selectivities based on appropriate solvents, temperatures, and Lewis acids [9][10][11]. A recent digest of RICR theorized an underlying mechanistic concept dubbed iodine-guided electrophilic aromatic substitution (IGEAS) [12]; the basis for which the work herein is titled. Other related

Hypervalent iodine-mediated Ritter-type amidation of terminal alkenes: The synthesis of isoxazoline and pyrazoline cores

• Sang Won Park,
• Soong-Hyun Kim,
• Jaeyoung Song,
• Ga Young Park,
• Darong Kim,
• Tae-Gyu Nam and
• Ki Bum Hong

Beilstein J. Org. Chem. 2018, 14, 1028–1033, doi:10.3762/bjoc.14.89

• -iodoxybenzoic acid) and DMP (Dess–Martin periodinane) (Table 1, entries 7 and 8) gave similar yields to the background reaction. Lastly, a Lewis acid screen (Table 1, entries 9–12) was performed. Among the tested Lewis acids, AlCl3, SnCl4, TiCl4, TMSOTf and BF3·Et2O, the latter was found to be the best choice

Recent advances in synthetic approaches for medicinal chemistry of C-nucleosides

• Kartik Temburnikar and
• Katherine L. Seley-Radtke

Beilstein J. Org. Chem. 2018, 14, 772–785, doi:10.3762/bjoc.14.65

• ][75][78]. Ribonolactone typically with its hydroxy groups protected, is amenable to nucleophilic substitutions [78][79]. Use of C-nucleophiles such as lithiated (hetero)aryls leads to C-C bond via a lactol intermediate (Figure 6A). Subsequent deoxygenation of the C1'–OH by Lewis acids (e.g., BF3·OEt2

AuBr₃-catalyzed azidation of per-O-acetylated and per-O-benzoylated sugars

• Jayashree Rajput,
• Srinivas Hotha and
• Madhuri Vangala

Beilstein J. Org. Chem. 2018, 14, 682–687, doi:10.3762/bjoc.14.56

• ][44][45]. More commonly, glycosyl azides are synthesized from per-O-acetylated sugars using trimethylsilyl azide in the presence of a variety of Lewis acids such as SnCl4 [46], TiCl4 [47][48], BF3·OEt2 [49], TMSOTf [50][51], etc. However, at higher concentration Lewis acids can potentially lead to

An air-stable bisboron complex: a practical bidentate Lewis acid catalyst

• Longcheng Hong,
• Sebastian Ahles,
• Andreas H. Heindl,
• Gastelle Tiétcha,
• Andrey Petrov,
• Zhenpin Lu,
• Christian Logemann and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2018, 14, 618–625, doi:10.3762/bjoc.14.48

• applicability [17]. To overcome this limitation we herein present a new catalyst (Scheme 1, B) with reasonable stability to air and moisture, which can be handled under ambient conditions and prepared with standard laboratory equipment. Results and Discussion Generally, the reactivity of boron Lewis acids is

• measured in CHCl3 and compared with pyridazine and bisborane A (concentrations: B: 4.52 × 10−5 mol/L, A: 4.52 × 10−5 mol/L, pyridazine: 3.68 × 10−5 mol/L). Bidentate bisborane Lewis acids. Complexation reaction of 5,10-dimethyl-5,10-dihydroboranthrene (A) with Lewis bases analyzed by NMR proton

Synthetic and semi-synthetic approaches to unprotected N-glycan oxazolines

• Antony J. Fairbanks

Beilstein J. Org. Chem. 2018, 14, 416–429, doi:10.3762/bjoc.14.30

• enzymes has therefore become an area of significant interest over the past 15 years [35][36]. The synthesis of N-glycan oxazolines Formation of glycosyl oxazolines Glycosyl oxazolines of monosaccharides can be produced straightforwardly using strong Lewis acids (e.g., FeCl3, SnCl4, or TMSOTf) and a fully

• -glycan oxazolines from peracetylated sugars using Lewis acids. Direct conversion of unprotected GlcNAc to a glycosyl oxazoline by treatment with DMC and Et3N in water. Total synthesis of a truncated complex biantennary N-glycan oxazoline via an epimerisation approach and Lewis acid mediated oxazoline

Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-λ⁶-sulfanyl)acetic acid esters with aldehydes

• Anna-Lena Dreier,
• Andrej V. Matsnev,
• Joseph S. Thrasher and
• Günter Haufe

Beilstein J. Org. Chem. 2018, 14, 373–380, doi:10.3762/bjoc.14.25

• on the initial formation of aldol addition products. These products could undergo acid catalyzed dehydration during aqueous work-up. Due to the presence of Lewis acids, which will be hydrolyzed, water would most probably eliminate via an intermediate benzyl cation, which would be stabilized by the

• conditions and application of enantiopure Lewis acids or SF5-substituted acetamides bearing a chiral auxiliary will result in asymmetric aldol addition reactions in the future. Conclusion From octyl SF5-acetate and TMSOTf/Et3N, a (Z)-enolate (ketene silylacetal) was preferentially formed as has already been

Synthesis and spectroscopic properties of β-meso directly linked porphyrin–corrole hybrid compounds

• Baris Temelli and
• Hilal Kalkan

Beilstein J. Org. Chem. 2018, 14, 187–193, doi:10.3762/bjoc.14.13

• the amount of 2a led to the formation of unidentified byproducts in the reaction medium and a reduction of the yield of 4a (Table 1, entry 9). Then, the activities of different catalysts, varying from clay catalysts to Lewis acids, were tested in the model reaction (Table 1, entries 10–19). AgOTf

Reagent-controlled regiodivergent intermolecular cyclization of 2-aminobenzothiazoles with β-ketoesters and β-ketoamides

• Irwan Iskandar Roslan,
• Kian-Hong Ng,
• Gaik-Khuan Chuah and
• Stephan Jaenicke

Beilstein J. Org. Chem. 2017, 13, 2739–2750, doi:10.3762/bjoc.13.270

• -aminobenzolthiazole (1a) and 1.0 mmol methyl acetoacetate (2a) gave a relatively poor yield of 5a (Table 2, entry 1). This prompted us to switch the equivalents of 1a and 2a to 1.0 and 1.5 mmol, respectively, which improved the yield tremendously (Table 2, entry 2). Hence, the survey of Lewis acids was conducted with

Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics

• Matthias Wünsch,
• David Schröder,
• Tanja Fröhr,
• Lisa Teichmann,
• Sebastian Hedwig,
• Nils Janson,
• Clara Belu,
• Jasmin Simon,
• Shari Heidemeyer,
• Philipp Holtkamp,
• Jens Rudlof,
• Lennard Klemme,
• Alessa Hinzmann,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2017, 13, 2428–2441, doi:10.3762/bjoc.13.240

• < toluene) have been described to enhance the stability of the transition state, improving the diastereomeric ratio, as well as the reactivity of the nucleophile, resulting in an improved yield [45]. As aldimines have been reported to be rather unreactive electrophiles [53], hard Lewis acids (AlMe3 > AlR3

• was reported to give very poor yields and low diastereoselectivity. In contrast to the argumentation of Xiao et al., who strongly recommended hard Lewis acids for the reaction of sulfinylimines with various ethynyllithium reagents [95], the crude imine 5k predominantly reacted with the Lewis acids Ti

• as colorless crystalline solids. It is assumed, that the undesired side products 9k and 10k were formed by a ligand transfer from the Lewis acids to imine 5k. Nucleophilic substitution of N/O-acetal 9k with two equivalents of (trimethylsilyl)ethynyllithium, in analogy to the conversions reported by

Intramolecular glycosylation

• Xiao G. Jia and
• Alexei V. Demchenko

Beilstein J. Org. Chem. 2017, 13, 2028–2048, doi:10.3762/bjoc.13.201

• was found to be the major product (5.2 to 1) compared to the intramolecular glycosylation product. The addition of Lewis acids helps to reduce the reaction time and the temperature required, but also increases the formation of hydrolysis products and reduces overall stereoselectivity. Recently, Liu et

Mechanochemical Knoevenagel condensation investigated in situ

• Sebastian Haferkamp,
• Franziska Fischer,
• Werner Kraus and
• Franziska Emmerling

Beilstein J. Org. Chem. 2017, 13, 2010–2014, doi:10.3762/bjoc.13.197

• synthesis in which bases or Lewis acids are used as catalysts, Kaupp et al. could reduce the amount of catalysts [21]. The Knoevenagel condensation of p-nitrobenzaldehyde with malononitrile was initially only accessible in melts at 150–170 °C or in the presence of a catalyst like calcite or fluorite [21][22

New bio-nanocomposites based on iron oxides and polysaccharides applied to oxidation and alkylation reactions

• Daily Rodríguez-Padrón,
• Alina M. Balu,
• Antonio A. Romero and
• Rafael Luque

Beilstein J. Org. Chem. 2017, 13, 1982–1993, doi:10.3762/bjoc.13.194

• mesostructured zeolitic materials. In particular, in this study, our research group has focused attention on the alkylation of toluene with benzyl chloride, since is promoted by the presence of Lewis acids such as iron oxides [49]. These two reactions in particular (oxidation and alkylation of benzyl alcohol and

Mechanochemical synthesis of small organic molecules

• Tapas Kumar Achar,
• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2017, 13, 1907–1931, doi:10.3762/bjoc.13.186

• reaction medium, solvent-free synthesis, microwave synthesis, use of different Lewis acids FeCl3, NiCl2, BiCl3, InBr3, use of Brønsted acids PTSA, etc. are also reported [129][130]. Recently, Mal and co-workers reported a mechanochemical Biginelli reaction by a subcomponent synthesis approach [131][132

Phenylsilane as an effective desulfinylation reagent

• Wanda H. Midura,
• Aneta Rzewnicka and
• Jerzy A. Krysiak

Beilstein J. Org. Chem. 2017, 13, 1513–1517, doi:10.3762/bjoc.13.150

• methodology [10][11][12][13][14]. Besides the well-known metal-catalyzed hydrosilylation, transition metals in the presence of Brønsted or Lewis acids were used for the reduction. Recently base-activated silanes were also used for this purpose [15][16][17]. Results and Discussion Our recent investigations

1-Imidoalkylphosphonium salts with modulated C_α–P⁺ bond strength: synthesis and application as new active α-imidoalkylating agents

• Jakub Adamek,
• Roman Mazurkiewicz,
• Anna Węgrzyk and
• Karol Erfurt

Beilstein J. Org. Chem. 2017, 13, 1446–1455, doi:10.3762/bjoc.13.142

• difficult and elaborate. Most of these, including the most frequently used α-alkoxy derivatives (Z = OR), N-[1-(benzotriazol-1-yl)alkyl]amides (Z = 1-benzotriazolyl) and 1-(N-acylamino)alkyl sulfones (Z = SO2Ar) require activation with Lewis acids, which are expensive (e.g., ZrCl4, VCl3, CeCl3, Bi(OTf)3 or

• InCl3) [11][17][19]. Moreover, the application of Lewis acids can diminish the activity of a reacting nucleophile, and usually requires a labor-intensive aqueous work-up procedure of the reaction mixture. The inevitable equilibrium between the N-acyliminium cation 3 and the less reactive uncharged N

Strategies toward protecting group-free glycosylation through selective activation of the anomeric center

• A. Michael Downey and
• Michal Hocek

Beilstein J. Org. Chem. 2017, 13, 1239–1279, doi:10.3762/bjoc.13.123

• -glucose in the presence of HCl to provide the methyl glycoside (pathway a, Scheme 6). The reaction proceeds chemoselective at the anomeric position. More recent examples typically use Lewis acids [29][30][31][32][33][34] or microwave irradiation [35][36] to accelerate the reaction. However, shortcomings

• very common and well-studied. Typical Lewis acids employed for anomeric activation are TMSOTf and BF3·Et2O (Scheme 14). The reactions proceed through an oxocarbenium ion that was very recently observed by NMR under cryogenic (−40 °C) conditions stabilized by the HF/SbF5 superacid [52]. The highly

Metal-free hydroarylation of the side chain carbon–carbon double bond of 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles in triflic acid

• Anna S. Zalivatskaya,
• Dmitry S. Ryabukhin,
• Marina V. Tarasenko,
• Alexander Yu. Ivanov,
• Irina A. Boyarskaya,
• Elena V. Grinenko,
• Ludmila V. Osetrova,
• Eugeniy R. Kofanov and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2017, 13, 883–894, doi:10.3762/bjoc.13.89

• protonation of the C=C bond of 1a in H2SO4 does not take place even at elevated temperature (75 °C, see Table 2, entry 1). Also, Lewis acids such as AlCl3 and AlBr3 are not effective in this transformation (Table 2, entries 2 and 3). The best results were obtained in neat TfOH. The substituents present in the

• action of TfOH at elevated temperature (60 °C) or for prolonged reaction times (12 or 24 h) at room temperature. See reviews [58][59] on the dealkylation of ethers by various Brønsted and Lewis acids. Additionally, the reactions were carried out under microwave (MW) irradiation (Table 3) analogously to

Synthesis of 1-indanones with a broad range of biological activity

• Marika Turek,
• Dorota Szczęsna,
• Marek Koprowski and
• Piotr Bałczewski

Beilstein J. Org. Chem. 2017, 13, 451–494, doi:10.3762/bjoc.13.48

• their synthesis (Figure 2). The commonly used reaction in this area is the Nazarov reaction which employs α,β-unsaturated ketones as substrates and is carried out in the presence of Brønsted or Lewis acids. Despite extensive studies on 1-indanones and their biological activity, this group of compounds

• yields of up to 74% and trace amounts of the auto-condensation products 6 (Scheme 3). Even in the deactivated derivatives containing halogen atoms at the aromatic system, the cyclopentanone ring closure took place quite easily [14]. If other Lewis acids, such as Bi(NTf2)3 or triflate derivatives of the

• C-4. By using catalytic amounts of Cu(OTf)2 or Cu(ClO4)2 as Lewis acids, cyclic products 134–137 have been obtained as single diastereoisomers in high yields (Figure 3). It has been proven that the reactivity and the selectivity of this cyclization can be controlled by positioning of the dienone 133

cis-Diastereoselective synthesis of chroman-fused tetralins as B-ring-modified analogues of brazilin

• Dimpee Gogoi,
• Runjun Devi,
• Pallab Pahari,
• Bipul Sarma and
• Sajal Kumar Das

Beilstein J. Org. Chem. 2016, 12, 2816–2822, doi:10.3762/bjoc.12.280

• triggering the reaction with other well-known Brønsted and Lewis acids possessing different activating abilities also led to the formation of the desired product (±)-5a with varying product yields (entries 1–15, Table 1). For example, when we conducted the reaction in toluene in the presence of 20 mol % of

• were used as catalysts (Table 1, entries 8–10) in toluene as reaction medium. Among the five different Lewis acids we screened (Table 1, entries 11–15), the best result was achieved by using BF3·OEt2 (Table 1, entry 12). Undoubtedly, the IFCEA cyclization proceeded almost equally well with different

• Lewis acids (Table 1, entries 11–15). However, all of these protocols required strict anhydrous conditions and some special attention to handle small amounts of the catalyst. On the other hand, TsOH·H2O is easily accessible, cheap, air stable, and even a minute amount can be weighed comfortably in an

Selective synthesis of thioethers in the presence of a transition-metal-free solid Lewis acid

• Federica Santoro,
• Matteo Mariani,
• Federica Zaccheria,
• Rinaldo Psaro and
• Nicoletta Ravasio

Beilstein J. Org. Chem. 2016, 12, 2627–2635, doi:10.3762/bjoc.12.259

• the green chemistry point of view would be the direct substitution of alcohols (that are also available at low cost) with thiols. In this case the only byproduct will be water. However, due to the lack of a good leaving group the use of an acid catalyst is mandatory. Both Brønsted and Lewis acids can

• be used. The former ones, such as free or polymer bound p-toluenesulfonic acid, promote the formation of significant amounts of by-products and can give yields in the range of 80% only for propargylic, allylic or benzylic alcohols [10][11][12][13][14]. As far as Lewis acids are concerned ZrCl4 [15

Et₃B-mediated and palladium-catalyzed direct allylation of β-dicarbonyl compounds with Morita–Baylis–Hillman alcohols

• Ahlem Abidi,
• Yosra Oueslati and
• Farhat Rezgui

Beilstein J. Org. Chem. 2016, 12, 2402–2409, doi:10.3762/bjoc.12.234

• ], and palladium (0, II) [9][10] as the catalyst or by converting the allylic alcohols into esters of inorganic acids, e.g., As2O3 [11], B2O3 [12], CO2 [13][14]. More recently the Lewis acids, such as, Ti(OiPr )4 [15], BEt3 [16][17][18][19], BPh3 [20], SnCl2 [21], and FeCl3 [22], have also been reported

Enduracididine, a rare amino acid component of peptide antibiotics: Natural products and synthesis

• Darcy J. Atkinson,
• Briar J. Naysmith,
• Daniel P. Furkert and
• Margaret A. Brimble

Beilstein J. Org. Chem. 2016, 12, 2325–2342, doi:10.3762/bjoc.12.226

• reaction site and poor compatibility of the cyclic guanidine motif with Lewis acids. Initial attempts to glycosylate cyclic guanidine 91 using an array of donors under Lewis acidic or basic conditions failed to provide access to N-mannosylguanidine 92 (Scheme 18). However, gold(I) mediated [71] N

Tunable microwave-assisted method for the solvent-free and catalyst-free peracetylation of natural products

• Manuela Oliverio,
• Paola Costanzo,
• Monica Nardi,
• Carla Calandruccio,
• Raffaele Salerno and
• Antonio Procopio

Beilstein J. Org. Chem. 2016, 12, 2222–2233, doi:10.3762/bjoc.12.214

• preferably acetic anhydride in solvent free conditions, in presence of non-toxic homogeneous catalysts such as environmental safe Lewis acids [13][14]. Moreover, the need to easily recover and reuse the catalyst, thus reducing the work-up procedure to a simple filtration, resulted in the growing use of