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

Diels–Alder reactions in confined spaces: the influence of catalyst structure and the nature of active sites for the retro-Diels–Alder reaction

• Ángel Cantín,
• M. Victoria Gomez and
• Antonio de la Hoz

Beilstein J. Org. Chem. 2016, 12, 2181–2188, doi:10.3762/bjoc.12.208

• reversibility of the reaction, homogeneous Lewis acids [1][2][3][4], solid acids [5][6] as catalyst, high pressures [6][7][8] and/or water as a solvent [9][10] have been reported. In particular, and among the most interesting environmental-friendly reactions, the cycloaddition reaction occurs with high

Superelectrophilic activation of 5-hydroxymethylfurfural and 2,5-diformylfuran: organic synthesis based on biomass-derived products

• Dmitry S. Ryabukhin,
• Dmitry N. Zakusilo,
• Mikhail O. Kompanets,
• Anton A.Tarakanov,
• Irina A. Boyarskaya,
• Tatiana O. Artamonova,
• Mikhail A. Khohodorkovskiy,
• Iosyp O. Opeida and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2016, 12, 2125–2135, doi:10.3762/bjoc.12.202

• strong Lewis acids (AlX3, X = Cl, Br) by their coordination with basic centers of organic compounds, or with acidic zeolites, possessing both Brønsted and Lewis acidity [33]. The main goal of this work was a study of reactions of 5-HMF and 2,5-DFF with arenes under electrophilic activation with Brønsted

• formation of 5-diarylmethylfurfurals 5a–g (Table 5, Figure 2). Contrary to compound 1a, which was activated with the Brønsted superacid TfOH to achieve Friedel–Crafts products 3 and 4 (Table 3 and Table 4), compound 2 gave better results with strong Lewis acids AlX3 (X = Cl, Br) (Table 5, entries 4, 5, 9

Microwave-assisted cyclizations promoted by polyphosphoric acid esters: a general method for 1-aryl-2-iminoazacycloalkanes

• Jimena E. Díaz,
• María C. Mollo and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2016, 12, 2026–2031, doi:10.3762/bjoc.12.190

• in a closed vessel reactor. The reaction was completed after 5 minutes at 100 °C and 1-(p-tolyl)-2-iminopyrrolidine (2a) was obtained in 86% yield (Table 1, entry 1). No reaction occurred in the absence of PPE, while the use of classical Lewis acids (ZnCl2, AlCl3, BF3) as cyclization agents led to

• affords the desired compounds in good to high yields and avoids the use of protic acids. Noteworthly, classical Lewis acids failed to efficiently promote this transformation. To our knowledge, this is the first method which allows the synthesis of the hitherto unreported N-aryl 7-membered heterocycles

Stereo- and regioselectivity of the hetero-Diels–Alder reaction of nitroso derivatives with conjugated dienes

• Lucie Brulíková,
• Aidan Harrison,
• Marvin J. Miller and
• Jan Hlaváč

Beilstein J. Org. Chem. 2016, 12, 1949–1980, doi:10.3762/bjoc.12.184

• when the reaction was performed in the presence of Lewis acids [142]. In 2004, the Yamamoto group reported results from an asymmetric nitroso hetero-Diels–Alder reaction between 6-substituted nitrosopyridine 195 (where R1 = H) and 1,3-cyclohexadienes 196 using Cu(PF6)(MeCN)4-(S)-BINAP (198) as the

Ionic liquids as transesterification catalysts: applications for the synthesis of linear and cyclic organic carbonates

• Maurizio Selva,
• Alvise Perosa,
• Sandro Guidi and
• Lisa Cattelan

Beilstein J. Org. Chem. 2016, 12, 1911–1924, doi:10.3762/bjoc.12.181

• protonation or quaternization of neutral precursors (imidazoles, amines, phosphines, pyridine or sulfides) with Brønsted acids or haloalkanes/dialkylsulfates, respectively. In the next step, a variety of ionic liquids are obtainable by anion exchange, either through direct treatments with Lewis acids or by

• Brønsted and Lewis acids, respectively [54]. A model case is [HSO3-BMIM]HSO4–Fe2(SO4)3 that offered an excellent catalytic performance in the transesterification of Camptotheca acuminata seed oil with methanol, with substantially quantitative conversions achieved in only 60 minutes at 60 °C. The

Practical synthetic strategies towards lipophilic 6-iodotetrahydroquinolines and -dihydroquinolines

• David R. Chisholm,
• Garr-Layy Zhou,
• Ehmke Pohl,
• Roy Valentine and
• Andrew Whiting

Beilstein J. Org. Chem. 2016, 12, 1851–1862, doi:10.3762/bjoc.12.174

• the inexpensive 3,3-dimethylallyl bromide/chloride, followed by cyclisation mediated by Lewis acids, or under acidic conditions [5][6]. A second, analogous approach involves an initial acylation with the commercially available 3,3-dimethylacryloyl chloride, followed by Friedel–Crafts cyclisations that

• also use Lewis acids [7]. The resultant quinolin-2-one is then reduced using strong hydride reducing agents such as LiAlH4 [8]. Similar THQs have also been prepared by a reductive Beckmann rearrangement of an oxime using diisobutylaluminium hydride (DIBAL) [9]. In contrast to this variety, the

• reaction, and a third synthetic route was therefore devised that would employ this methodology. A common approach in the literature towards similar THQs involves an initial acylation of the starting aniline using 3,3-dimethylacryloyl chloride, followed by a high temperature cyclisation employing Lewis

Synthesis of the C8’-epimeric thymine pyranosyl amino acid core of amipurimycin

• Pramod R. Markad,
• Navanath Kumbhar and
• Dilip D. Dhavale

Beilstein J. Org. Chem. 2016, 12, 1765–1771, doi:10.3762/bjoc.12.165

• -acetylamino)-6-chloropurine 17, under a variety of reaction conditions, of solvents, temperature, Lewis acids as well as the use of the thymine nucleobase 18 (Scheme 4) failed to provide the desired nucleoside. Knowing the fact that the glycosylation reaction is severely influenced by numerous factors

TMSBr-mediated solvent- and work-up-free synthesis of α-2-deoxyglycosides from glycals

• Mei-Yuan Hsu,
• Yi-Pei Liu,
• Sarah Lam,
• Su-Ching Lin and
• Cheng-Chung Wang

Beilstein J. Org. Chem. 2016, 12, 1758–1764, doi:10.3762/bjoc.12.164

• anomeric mixtures [10]. Glycals have been considered as alternative precursors for producing 2-deoxythioglycosides as well as oligosaccharides. Several methods based on the use of glycals in the presence of Lewis acids for S- or O-2-deoxyglycoside preparations have been developed [51][52][53][54][55][56

• ][57][58][59][60][61][62][63]. However, based on the hard and soft (Lewis) acids and bases (HSAB) theory, hard acids would coordinate to the harder O3 in glycals in preference to the softer alkene to initiate an undesired Ferrier rearrangement, leading to the formation of a considerable amount of 2,3

Rearrangements of organic peroxides and related processes

• Ivan A. Yaremenko,
• Vera A. Vil’,
• Dmitry V. Demchuk and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2016, 12, 1647–1748, doi:10.3762/bjoc.12.162

• based on Pt [208], Zr [209], Re [210][211], Se [212][213], As [205], Mo [214], Co [215], Brønsted [216], and Lewis acids [217] are described in the literature. The general mechanism of a Lewis acid-catalyzed Baeyer–Villiger rearrangement is presented in Scheme 3 [200][218]. Scheme 4 shows the

Experimental and theoretical insights in the alkene–arene intramolecular π-stacking interaction

• Valeria Corne,
• Ariel M. Sarotti,
• Carmen Ramirez de Arellano,
• Rolando A. Spanevello and
• Alejandra G. Suárez

Beilstein J. Org. Chem. 2016, 12, 1616–1623, doi:10.3762/bjoc.12.158

• S/R ratios are considerable high in the absence of Lewis acids. The high inductive capacity is interpreted in terms of the fact that the conformation of the dienophile is fixed by a π-stacking interaction. The reactions promoted by Et2AlCl produced the reversed endo S/R diastereoselectivity with a

On the cause of low thermal stability of ethyl halodiazoacetates

• Magnus Mortén,
• Martin Hennum and
• Tore Bonge-Hansen

Beilstein J. Org. Chem. 2016, 12, 1590–1597, doi:10.3762/bjoc.12.155

• ]. The synthesis and properties of diazo compounds have been a topic of much interest, particularly relevant are their thermal stability and sensitivity towards Brønsted and Lewis acids. The monograph by Regitz and Maas gives an excellent overview on their preparation and properties [3]. The thermal

• diazoacetate (EDA) is relatively safe to handle, being thermally stable at room temperature with a reported half-life of 109 hours at 100 °C [3]. EDA is also stable in weakly acidic solutions such as glacial acid [4], but reactive in the presence of Lewis acids, a key property for its effectiveness in

• us wonder whether halodiazoacetates have an increased sensitivity (relative to EDA) towards Brønsted and Lewis acids in general. During our previous studies we made the same observations that were originally reported by Schöllkopf [6]. The halodiazoesters readily decompose at room temperature within

Biosynthesis of oxygen and nitrogen-containing heterocycles in polyketides

• Franziska Hemmerling and
• Frank Hahn

Beilstein J. Org. Chem. 2016, 12, 1512–1550, doi:10.3762/bjoc.12.148

• presence of Lewis acids is a common synthetic strategy for making pyrans and furans. Hemiacetals are also biosynthesis intermediates where they are transformed into individually functionalised heterocycles or acetals. In many cases, these hemiacetals are also appropriately activated to react further

The hydrolysis of geminal ethers: a kinetic appraisal of orthoesters and ketals

• Sonia L. Repetto,
• James F. Costello,
• Craig P. Butts,
• Joseph K. W. Lam and
• Norman M. Ratcliffe

Beilstein J. Org. Chem. 2016, 12, 1467–1475, doi:10.3762/bjoc.12.143

• preferential cleavage with Lewis acids [31]. The Cambridge Structural Database (2015) [32] contains a single example of a five-membered 1,3-dioxolane orthoester [33]. Here, the ring adopts a distorted half-chair (C2) arrangement with a dihedral angle θ [O–C(4)–C(5)–O] = 32° [Figure 2a – ZICMED viewed C(4)→C(5

Synergistic chiral iminium and palladium catalysis: Highly regio- and enantioselective [3 + 2] annulation reaction of 2-vinylcyclopropanes with enals

• Haipan Zhu,
• Peile Du,
• Jianjun Li,
• Ziyang Liao,
• Guohua Liu,
• Hao Li and
• Wei Wang

Beilstein J. Org. Chem. 2016, 12, 1340–1347, doi:10.3762/bjoc.12.127

• amine I in CH2Cl2 at rt for 48 h (Table 1). A series of Lewis acids were initially screened. FeCl3 and Cu(OTf)2 gave the 1,2-cycloaddition product tetrahydrofuran 4a (Table 1, entries 1 and 2). It is also disappointing that others Lewis acids, such as CuCl2, MgI2, ZnBr2, ZnCl2 and FeCl2 failed to

Artificial Diels–Alderase based on the transmembrane protein FhuA

• Hassan Osseili,
• Daniel F. Sauer,
• Klaus Beckerle,
• Marcus Arlt,
• Tomoki Himiyama,
• Tino Polen,
• Akira Onoda,
• Ulrich Schwaneberg,
• Takashi Hayashi and
• Jun Okuda

Beilstein J. Org. Chem. 2016, 12, 1314–1321, doi:10.3762/bjoc.12.124

• reported. The Diels–Alder reaction is a powerful C–C bond formation reaction, widely used in organic chemistry, e.g., for the synthesis of natural products [28]. This reaction is known to be catalyzed by Lewis acids such as a Cu(II) complex [29]. Additionally, structurally defined catalysts are found to

Multicomponent reactions: A simple and efficient route to heterocyclic phosphonates

• Mohammad Haji

Beilstein J. Org. Chem. 2016, 12, 1269–1301, doi:10.3762/bjoc.12.121

• H2SO4 or Lewis acids such as SnCl2, FeCl3 and VCl3, as well as heterogeneous catalysts including silica gel supported sulfuric acid and sodium hydrogen sulfate did not affect this reaction. Also, the reaction in the presence of p-toluenesulfonic acid (TsOH), in aprotic solvents proceeded with much

• )phosphonates 98 in the presence of various Lewis acids (Scheme 22) [47][48]. This reaction, under catalyst-free conditions or in the presence of Lewis acids such as FeCl3, CBr4, In(OTf)3, Bi(OTf)3, and Yb(OTf)3, exclusively yielded the acyclic α-aminophosphonates 99. However, the reaction in the presence of

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• are further classified according to whether catalysis is achieved with chiral Lewis acids, organocatalysts, or transition metals. Keywords: asymmetric catalysis; conjugate addition; enantioselective protonation; enolate; Introduction Due to their ubiquity in natural products and drugs, many

• –enantioselective protonation reactions that have been reported in the literature. These reports have been grouped by class of Michael acceptor and further subdivided by the type of catalyst system used (Lewis acids, organocatalysts and transition metals). While numerous efficient methods have been developed for

• hydrogen atom transfer are also included in this review. Review α,β-Unsaturated esters Lewis acids α,β-Unsaturated esters have been the most extensively studied class of electrophiles for conjugate addition–enantioselective protonation sequences. Esters are useful functional group handles for additional

Catalytic asymmetric synthesis of biologically important 3-hydroxyoxindoles: an update

• Bin Yu,
• Hui Xing,
• De-Quan Yu and
• Hong-Min Liu

Beilstein J. Org. Chem. 2016, 12, 1000–1039, doi:10.3762/bjoc.12.98

• also been studied for the total synthesis of natural products and accessing biologically important scaffolds. In 2012, Bisai et al. reported the Lewis acid-catalyzed Friedel–Crafts alkylation of 3-hydroxy-2-oxindoles with electron-rich phenols (Scheme 46) [63]. They found that various Lewis acids (e.g