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

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

• , 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

Enantioselective PCCP Brønsted acid-catalyzed aza-Piancatelli rearrangement

• Gabrielle R. Hammersley,
• Meghan F. Nichol,
• Helena C. Steffens,
• Jose M. Delgado,
• Gesine K. Veits and
• Javier Read de Alaniz

Beilstein J. Org. Chem. 2019, 15, 1569–1574, doi:10.3762/bjoc.15.160

• aza-Piancatelli reaction, we sought to identify other asymmetric catalytic systems capable of controlling the absolute stereochemistry. To this end, we envisioned that the chiral pentacarboxycyclopentadiene (PCCP) Brønsted acid catalyst (8) recently developed by the Lambert lab might be suitable

• (Figure 1) [38]. First, the pKa values measured in acetonitrile (MeCN) are lower than chiral phosphoric acids (Brønsted acid pKa = 8.85 vs chiral phosphoric acids pKa = 12–14) [38]. Given the enhanced acidity, we reasoned that this type of chiral Brønsted acid catalyst could facilitate the dehydration

• . Finally, this new catalyst can be produced inexpensively and on scale, features that are attractive for developing a wide range of asymmetric transformations. Results and Discussion Herein, we describe our initial efforts in this area using chiral Brønsted acid catalyst 8. Our investigations began by

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

Robust perfluorophenylboronic acid-catalyzed stereoselective synthesis of 2,3-unsaturated O-, C-, N- and S-linked glycosides

• Madhu Babu Tatina,
• Xia Mengxin,
• Rao Peilin and
• Zaher M. A. Judeh

Beilstein J. Org. Chem. 2019, 15, 1275–1280, doi:10.3762/bjoc.15.125

• developed for the synthesis of 2,3-unsaturated C-, O-, N- and S-linked glycosides (enosides) using 20 mol % perflurophenylboronic acid catalyst via Ferrier rearrangement. Using this protocol, D-glucals and L-rhamnals reacted with various C-, O-, N- and S-nucleophiles to give a wide range of glycosides in up

• results obtained using boron trifluoride diethyl etherate [32]. We then applied the perfluorophenylboronic acid catalyst to promote the reaction between 2,3,4,6-tetra-O-acetyl-D-glucal (4a) and O- and S-nucleophiles (Figure 2). The Ferrier-catalyzed rearrangements of 2-substituted sugars such as 2,3,4,6

• blocks especially for natural product synthesis [36][37][38][39][40]. Therefore, we used the perfluorophenyl boronic acid catalyst in the reaction between 2,3,4,6-tetra-O-acetyl-D-glucal (1a) and benzyl alcohol, n-butyl alcohol, cyclohexyl alcohol and p-toluenethiol (Figure 2). Gratifyingly, the reaction

Extending mechanochemical porphyrin synthesis to bulkier aromatics: tetramesitylporphyrin

• Qiwen Su and
• Tamara D. Hamilton

Beilstein J. Org. Chem. 2019, 15, 1149–1153, doi:10.3762/bjoc.15.111

• work on mechanochemical porphyrin synthesis has demonstrated that it is possible to synthesize tetraphenylporphyrin (TPP) by grinding benzaldehyde and pyrrole (two liquids) in the presence of an acid catalyst, followed by oxidation with DDQ in minimal amounts of solvent [19]. TPP was produced in a

• the first-reported conditions of the Lindsey synthesis, mesitaldehyde “failed to give good yields” of TMP [11]. Later studies of modified reaction conditions employing boron trifluoride as the acid catalyst, and small amounts of ethanol as a co-catalyst, were successful in producing TMP with yields

• of an acid catalyst and ground using a mixer mill for 10 minutes (Scheme 2), a pink powder is formed. As in the case of benzaldehyde, the powder is found to contain no porphyrin, evidenced by the lack of a Soret band at 410–420 nm in the electronic spectrum. Our work with benzaldehyde showed that

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

• 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

Tuning the stability of alkoxyisopropyl protection groups

• Zehong Liang,
• Henna Koivikko,
• Mikko Oivanen and
• Petri Heinonen

Beilstein J. Org. Chem. 2019, 15, 746–751, doi:10.3762/bjoc.15.70

• ’-acetal-protected 2’-deoxythymidines were prepared using 7 equiv of the appropriate reagent 1a–e with the suitably protected thymidine 2 or 5 (Scheme 1) in the presence of p-toluenesulfonic acid as the acid catalyst. A suitable amount of the acid catalyst is 0.5 to 1 mol %, with which the reaction takes

• exception, as the electron-withdrawing trifluoroethyl group reduces the reactivity and the reaction time had to be increased to several hours. In addition, the yields of the protected products 3e and 6e also remained rather low, around 35%. If a larger amount than 1 mol % of the acid catalyst is used and

Syntheses and chemical properties of β-nicotinamide riboside and its analogues and derivatives

• Mikhail V. Makarov and
• Marie E. Migaud

Beilstein J. Org. Chem. 2019, 15, 401–430, doi:10.3762/bjoc.15.36

• an acid catalyst (Scheme 14). Conditions which use p-toluenesulfonic acid in acetone [58] produced acetonide 29 in 49% yield after column chromatography. Conditions which employed concentrated sulfuric acid in acetonitrile [59][60] yielded the acetonide in 76–96% yield. Large excess of 2,2

Olefin metathesis catalysts embedded in β-barrel proteins: creating artificial metalloproteins for olefin metathesis

• Daniel F. Sauer,
• Johannes Schiffels,
• Takashi Hayashi,
• Ulrich Schwaneberg and
• Jun Okuda

Beilstein J. Org. Chem. 2018, 14, 2861–2871, doi:10.3762/bjoc.14.265

• ions such as Mg, Ca, Mn, Fe, Ni, Co, Cu, Zn etc. within a protein are abundant in nature [24]. As metalloenzymes, these metalloproteins are capable of catalyzing various important reactions in biosynthesis and key steps in cellular energy metabolism. The embedded metal ion mainly acts as a Lewis acid

• catalyst or redox catalyst. Various metalloenzymes have been applied in laboratory-scale reactions and a few metalloenzymes such as nitrile hydratase (cobalt(III) in the active site) for the production of acrylamide have found application in industry [25]. Notably, however, the reaction scope of natural

Synthesis of unnatural α-amino esters using ethyl nitroacetate and condensation or cycloaddition reactions

• Glwadys Gagnot,
• Vincent Hervin,
• Eloi P. Coutant,
• Sarah Desmons,
• Racha Baatallah,
• Victor Monnot and
• Yves L. Janin

Beilstein J. Org. Chem. 2018, 14, 2846–2852, doi:10.3762/bjoc.14.263

• -(trifluoromethyl)benzaldehyde (3j) and acetic anhydride using indium(III) chloride [15] as a Lewis acid catalyst [16] without any solvent at room temperature pointed out a complete conversion into acylal 7 overnight. A similar reaction using pivaloyl anhydride and either indium(III) chloride or tetrafluoroboric

An overview on recent advances in the synthesis of sulfonated organic materials, sulfonated silica materials, and sulfonated carbon materials and their catalytic applications in chemical processes

• Hashem Sharghi,
• Pezhman Shiri and
• Mahdi Aberi

Beilstein J. Org. Chem. 2018, 14, 2745–2770, doi:10.3762/bjoc.14.253

• trimethylsilylated phenyl-modified SBA-15 78. This white solid was reacted with ClSO3H to get SBA-15 functionalized with phenyl sulfonic acid groups (SBA-15-Ph-SO3H, 79, Scheme 14). The SBA-15-Ph-SO3H catalyst 79 is a hydrophobic nanoreactor solid acid catalyst that presents a series of advantages, such as

• intermediate IV. Finally, this intermediate is split by a nucleophilic attack of hydroxyl radicals to afford byproducts (including acetic acid, acetanilide, and formic acid) and desired product. The proposed mechanism was confirmed by EPR spectrum. The SSA catalyst is an inexpensive and reusable solid acid

• catalyst [63]. 4. Synthetic strategies of carbon-based materials and functionalized carbon-based materials containing sulfonic acid groups as a diverse class of catalysts and their uses in organic reactions Carbon-based materials containing sulfonic acid groups [33] have been used as novel, efficient, and

Microwave-assisted synthesis of biologically relevant steroidal 17-exo-pyrazol-5'-ones from a norpregnene precursor by a side-chain elongation/heterocyclization sequence

• Gergő Mótyán,
• László Mérai,
• Márton Attila Kiss,
• Zsuzsanna Schelz,
• Izabella Sinka,
• István Zupkó and
• Éva Frank

Beilstein J. Org. Chem. 2018, 14, 2589–2596, doi:10.3762/bjoc.14.236

• phenylhydrazine (5b) was completed within 7 h in refluxing EtOH in the presence of an acid catalyst. A reduction of the reaction time to 3 h could be achieved by changing the solvent to AcOH affording the desired product 6b in high yield (86%, Scheme 2). On the other hand, the reaction of 4 with methylhydrazine

β-Hydroxy sulfides and their syntheses

• Mokgethwa B. Marakalala,
• Edwin M. Mmutlane and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1668–1692, doi:10.3762/bjoc.14.143

• acid catalyst for the asymmetric ring opening of cyclohexene oxide with alkyl- and arylthiols [37]. The optimal conditions were found to be 10 mol % of the catalyst relative to cyclohexene oxide, at room temperature, in dichloromethane as the solvent (Scheme 11). More polar solvents such as DMF

Glycosylation reactions mediated by hypervalent iodine: application to the synthesis of nucleosides and carbohydrates

• Yuichi Yoshimura,
• Hideaki Wakamatsu,
• Yoshihiro Natori,
• Yukako Saito and
• Noriaki Minakawa

Beilstein J. Org. Chem. 2018, 14, 1595–1618, doi:10.3762/bjoc.14.137

• donor of in the latter are carried out in the presence of an appropriate activator. As an activator of the glycosylation, a combination of a Lewis acid catalyst and a hypervalent iodine was developed for synthesizing 4’-thionucleosides, which could be applied for the synthesis of 4’-selenonucleosides as

• oxidative conditions. These were quite useful and the conceptually similar reactions were widely used for synthesizing nucleoside derivatives. Recently, a combination of a Lewis acid catalyst and hypervalent iodine was developed for synthesizing 4’-thionucleosides, which was based on a Pummerer-type

• alcohol 11. The most popular method to form a glycosyl bond between the sugar moiety and the base of a nucleoside is a Vorbrüggen reaction [15][16], in which a silylated base and sugar donor, e.g., 1-acetoxy sugar, are condensed by a Lewis acid catalyst. It was clear that this reaction could also be used

Synthesis of pyrazolopyrimidinones using a “one-pot” approach under microwave irradiation

• Mark Kelada,
• John M. D. Walsh,
• Robert W. Devine,
• Patrick McArdle and
• John C. Stephens

Beilstein J. Org. Chem. 2018, 14, 1222–1228, doi:10.3762/bjoc.14.104

• -ketonitrile in the presence of a hydrazine [1][2][3][4][19][20][21][22][23][24][25][26][27][28][29], with Rao et al. [31] and Bagley et al. [32] reporting microwave-assisted protocols, the former requiring an acid catalyst. In order to conduct a solvent screen we chose β-ketonitrile 1a as a model substrate

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• prepared by reacting α-tetralone (171) with ethyl orthoformate in the presence of an acid catalyst. Subsequent successive reactions are dihalocarbene addition to enolether 172, ring expansion of the adduct 173 to halocycloheptadienone 168, and dehydrohalogenation of 168 with lithium chloride. Later

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

• -orbital of the boron atom. This may prevent the boron compound from decomposition as well as hydrolysis and provide a practical Lewis acid catalyst for organic reactions. To test the hypothesis, several Lewis bases were subjected to the coordination reaction with the bidentate bisboron catalyst, 5,10

• + Na]+ calcd for C18H18B2N2, 307.1548; found, 307.1561; IR (neat): 3124, 3041, 2965, 2918, 2829, 1581, 1468, 1425, 1310, 1286, 1276, 1153, 1113, 997, 950, 889, 754, 713, 610, 575. IEDDA reactions catalyzed by the air-stable bidentate Lewis acid catalyst B General procedure A for IEDDA reactions of

• phthalazine: In a Schlenk tube charged with a stirring bar, the air-stable bidentate Lewis acid catalyst B (5.00 mol %) and the stated solvent were added under N2. Then, the phthalazine (1.00 equiv), dienophile (2.00 equiv; for enamines, generated in situ from aldehyde and amine) were added subsequently. The

Synthesis and stability of strongly acidic benzamide derivatives

• Frederik Diness,
• Niels J. Bjerrum and
• Mikael Begtrup

Beilstein J. Org. Chem. 2018, 14, 523–530, doi:10.3762/bjoc.14.38

• p-toluenesulfonic acid (5) which is commonly used as a soluble organic acid catalyst in chemical reactions. Remarkably, neither the N-triflylbenzamides nor the N,N’-bis(triflyl)benzimidamides have been studied as Brønsted acid catalysts. Their chemical stability including compatibility with

Acid-catalyzed ring-opening reactions of a cyclopropanated 3-aza-2-oxabicyclo[2.2.1]hept-5-ene with alcohols

• Katrina Tait,
• Alysia Horvath,
• Nicolas Blanchard and
• William Tam

Beilstein J. Org. Chem. 2017, 13, 2888–2894, doi:10.3762/bjoc.13.281

• -oxabicyclo[2.2.1]alkenes reductively cleave the N–O bond (a) (Scheme 4), therefore, no examples cleaving the C–O bond have been reported in the literature. In this paper, we aim to explore the use of an acid catalyst with an alcohol nucleophile on the ring-opening of cyclopropanated 3-aza-2-oxabicyclic

• A variety of different acid catalysts was screened and the results are summarized in Table 1. In the presence of a Lewis acid catalyst (Table 1, entries 1–3), the reaction did not proceed as seen with FeCl3 (Table 1, entry 1) or produced ring-opened product 26 in low yields (Table 1, entries 2 and 3

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

• and amides have been developed, controlled by the reagents employed. With the Brønsted base KOt-Bu and CBrCl3 as radical initiator, benzo[d]imidazo[2,1-b]thiazoles are synthesized via attack at the α-carbon and keto carbon of the β-ketoester moiety. In contrast, switching to the Lewis acid catalyst

• ][21][22]. Interestingly, by replacing the radical initiator and Brønsted base system with a Lewis acid catalyst, benzo[4,5]thiazolo[3,2-a]pyrimidin-4-ones were formed instead (Scheme 1b). This highlights the versatility of β-ketoesters where the regioselectivity of the reaction is directed by the

Novel approach to hydroxy-group-containing porous organic polymers from bisphenol A

• Tao Wang,
• Yan-Chao Zhao,
• Li-Min Zhang,
• Yi Cui,
• Chang-Shan Zhang and
• Bao-Hang Han

Beilstein J. Org. Chem. 2017, 13, 2131–2137, doi:10.3762/bjoc.13.211

• the stretching vibration of methyl groups shows quantitative changes between BPA and PPOPs, suggesting the degradation of BPA in o-dichlorobenzene and it is reported that the cleavage of methylene can be catalyzed under acidic or basic conditions [29][30]. p-Toluenesulfonic acid acted as an acid

• catalyst in this contribution and will promote the cleavage of BPA at high temperature. The broad absorption bands located at ca. 3500 cm−1 is attributed to the characteristic stretching vibration of hydroxy groups, which is consistent with the literature data [25]. The absorption peak at 1705 cm−1

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

• . The quantity of probe molecule adsorbed by the solid acid catalyst can subsequently be easily quantified. In order to distinguish between Lewis and Brønsted acidity, it was assumed that all DMPY selectively titrates Brønsted sites (methyl groups hinder coordination of nitrogen atoms with Lewis acid

New tricks of well-known aminoazoles in isocyanide-based multicomponent reactions and antibacterial activity of the compounds synthesized

• Maryna V. Murlykina,
• Maryna N. Kornet,
• Sergey M. Desenko,
• Svetlana V. Shishkina,
• Oleg V. Shishkin,
• Aleksander A. Brazhko,
• Vladimir I. Musatov,
• Erik V. Van der Eycken and
• Valentin A. Chebanov

Beilstein J. Org. Chem. 2017, 13, 1050–1063, doi:10.3762/bjoc.13.104

• -binucleophile, acid – catalyst). Literature data indicate [14][25][59][97][98][99][100][101] that 5-aminopyrazoles bearing in the fourth position electron-withdrawing substituents like carboxamide, carboxylate or a carbonitrile group, posses chemical properties being different from other 5-aminopyrazoles but

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

• Friedel–Crafts cyclization (Scheme 2, upper panel) and the products are relevant in the field of natural product-like molecules, because the synthesized molecules are close analogs of a natural product (brazilin). Moreover, the use of TsOH·H2O as an easily-accesible Brønsted acid catalyst with low loading