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

• 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

• best of our knowledge, up to the moment, there are no examples for an intermolecular hydroarylation of electron-deficient allenes by benzene derivatives under the action of strong Brønsted or Lewis acids. The main goals of this work were to study transformations of various phosphorylallenes under

• , entry 4). It is worth noting, that the use of other Lewis acids, NiCl2, EuCl3, FeCl3, CuOTf, AgNO3, did not activate allene 1a; in these reactions only the product of the hydrolysis 8 was finally isolated. The configuration of the carbon–carbon double bond in compounds Z-9, E-10b and Z-11a was

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

• presence of strong Lewis acids [36]. We herein report the design and exploration of a new trityl carbocation that has a chiral weakly coordinating Fe(III)-based phosphate anion for the effective asymmetric catalysis in the Diels–Alder reaction of anthracenes. Results and Discussion In our previous work, we

• phosphate anion (Scheme 2). Upon in situ mixing the chiral trityl phosphate (TP, 0.05 mM) and different Lewis acids (0.05 mM), such as InCl3, InBr3, InI3, In(OTf)3, Sc(OTf)3, Hf(OTf)3, GaCl3, and FeBr3, the originally colorless solution of the chiral trityl phosphate TP turned orange, suggesting the

• formation of tritylium ions (Scheme 2a). The stimulated trityl cation generation was probed by UV–vis spectroscopy. As shown in Figure 1a, when treated with different Lewis acids, trityl phosphate TP showed a variable tendency to dissociate into the free tritylium ion pair with InBr3 as the most active

Synthesis of non-racemic 4-nitro-2-sulfonylbutan-1-ones via Ni(II)-catalyzed asymmetric Michael reaction of β-ketosulfones

• Alexander N. Reznikov,
• Anastasiya E. Sibiryakova,
• Marat R. Baimuratov,
• Eugene V. Golovin,
• Victor B. Rybakov and
• Yuri N. Klimochkin

Beilstein J. Org. Chem. 2019, 15, 1289–1297, doi:10.3762/bjoc.15.127

• , which allows to obtain chiral cyclic sulfones with high enantioselectivity [10][11][12]. Also non-racemic cyclic sulfones can be obtained by the Diels–Alder reaction, catalyzed by chiral Lewis acids or organocatalysts. Rh- and Cu-catalyzed CH-insertion reactions occurring at moderate or high

• ketosulfones with nitroalkenes in the presence of organocatalysts shows high enantioselectivity, however, leads to a mixture of diastereomers. For the catalytic activation of β-ketosulfones by metal complexes chiral Lewis acids may be considered as an alternative way to carry out the asymmetric Michael

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

• ]. The Ferrier rearrangement is one of the most useful processes to synthesize pseudo-glycosides in a direct and stereoselective fashion. Several classes of catalysts have been successfully applied in the Ferrier rearrangement including Brønsted acids [7][8][9][10][11][12][13], Lewis acids [14][15][16

Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids

• Herman O. Sintim,
• Hamad H. Al Mamari,
• Hasanain A. A. Almohseni,
• Younes Fegheh-Hassanpour and
• David M. Hodgson

Beilstein J. Org. Chem. 2019, 15, 1194–1202, doi:10.3762/bjoc.15.116

• desilylation. Initial Lewis acids screened either failed to react (PdCl2(MeCN)2), or led to complex mixtures (BF3, YbOTf, TBSOTf). More encouragingly, both AlCl3 and FeCl3 were found to cleave the acetonide 19a at rt, with the TBDPS group only being partially lost (≈15%) in both cases. AlCl3 was observed to

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

• . Herein, we present the preliminary results of these studies. Results and Discussion Urea 4a (prepared by reacting propargylamine with 4-(trifluoromethoxy)benzyl isocyanate) was reacted with an equivalent amount of benzylamine in refluxing toluene in the presence of various Lewis acids. To our delight

The LANCA three-component reaction to highly substituted β-ketoenamides – versatile intermediates for the synthesis of functionalized pyridine, pyrimidine, oxazole and quinoxaline derivatives

• Tilman Lechel,
• Roopender Kumar,
• Mrinal K. Bera,
• Reinhold Zimmer and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2019, 15, 655–678, doi:10.3762/bjoc.15.61

• remarkable [41]. For subsequent reactions, alkoxy groups other than the methoxy group were desirable because the latter substituent can only be converted into free hydroxy groups by treatment with strong (Lewis) acids. We therefore examined benzyloxyallene as starting material in the three-component reaction

Tandem copper and photoredox catalysis in photocatalytic alkene difunctionalization reactions

• Nicholas L. Reed,
• Madeline I. Herman,
• Vladimir P. Miltchev and
• Tehshik P. Yoon

Beilstein J. Org. Chem. 2019, 15, 351–356, doi:10.3762/bjoc.15.30

• transition metals, Lewis acids, and organocatalysts has been productively utilized in asymmetric transformations [7][8][9], cross-couplings [10][11][12], and oxidative decarboxylation reactions [13][14], among others. The use of a cocatalyst to control these photochemical transformations enables reactions

Oxidative radical ring-opening/cyclization of cyclopropane derivatives

• Yu Liu,
• Qiao-Lin Wang,
• Zan Chen,
• Cong-Shan Zhou,
• Bi-Quan Xiong,
• Pan-Liang Zhang,
• Chang-An Yang and
• Quan Zhou

Beilstein J. Org. Chem. 2019, 15, 256–278, doi:10.3762/bjoc.15.23

• and aldehydes 48 to provide 2-acyl-3,4-dihydronaphthalenes 49 in moderate to excellent yields via a series of radical addition, ring-opening and cyclization in the presence of DTBP (di-tert-butyl peroxide) and Lewis acids (Scheme 12) [73]. Moreover, the experimental results showed MCPs 1 with electron

Generation of 1,2-oxathiolium ions from (arysulfonyl)- and (arylsulfinyl)allenes in Brønsted acids. NMR and DFT study of these cations and their reactions

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

Beilstein J. Org. Chem. 2018, 14, 2897–2906, doi:10.3762/bjoc.14.268

• work on transformations of phosphonoallenes under the action of strong Brønsted or Lewis acids [29][30][31][32], we undertook a special study on reactions of (arylsulfonyl)allenes 2a–j and (arylsulfinyl)allenes 1a,b (Scheme 1). The reaction between proparylic alcohols and arylsulfanyl chlorides

• from that, Lewis acids of various strength (AlCl3, AlBr3, FeCl3, CeCl3, BF3-Et2O, In(OTf)3) were found to be ineffective for this transformation, no reactions of allenes 2 occurred with them. Taking into account the data on the formation of cations B (Table 1), their electronic characteristics (Table 2

• to alcohols 7a,b. Conclusion Transformations of (arylsulfonyl)- and (arylsulfinyl)allenes under the action of the Brønsted superacid TfOH, or strong Lewis acids AlX3 (X = Cl, Br) have been studied. Under electrophilic conditions, these allenes form the corresponding 1,2-oxathiolium ions, which have

Synthesis of dihydroquinazolines from 2-aminobenzylamine: N³-aryl derivatives with electron-withdrawing groups

• Nadia Gruber,
• Jimena E. Díaz and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2018, 14, 2510–2519, doi:10.3762/bjoc.14.227

• , which are able at the same time, to activate nitrogen and oxygen functionalities towards nucleophilic attack. This dual behavior makes them valuable reagents, capable of promoting certain cyclodehydrations that cannot be achieved by using classical Lewis acids [84][85]. Additional advantages of PPA

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

• yield and high regioselectivity. As an alternative to Lewis acids, Cossy and co-workers reported the use of LiNTf2 promoter for the thiolysis of epoxides [29]. The reaction provided better yields under solvent-free conditions than using dichloromethane as a solvent. Although a wide variety of epoxides

• , the added advantage of the protocol is that when LiNTf2 is used instead of Lewis acids, the work-up is easier as no vexatious emulsion was formed. However, the need for 0.5 equiv of the promoter and the sluggishness (20 h) of the reaction make the method less favorable when compared to other Lewis

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

• construction of oligosaccharides is the combination of Lewis acids and iodine or its chemical equivalents. Fukase and co-workers reported a glycosylation reaction with thioglycoside using hypervalent iodine reagents in the 1990s [78][79]. The outline and postulated mechanism of the reaction are shown in Figure

•  7. The reaction of iodosylbenzene and electrophiles, e.g., triflic anhydride or Lewis acids, should generate a potent thiophile 143 that reacts with thioglycoside 144 to form an oxocarbenium ion 145. The resulting oxocarbenium ion 145 should in turn react with a sugar acceptor to give the

• glycosylated product 147 (Figure 7). By this reaction, Fukase et al. reported the glycosylation of methyl thioglycoside 148 as a sugar donor to give disaccharides 150 and 152 in high chemical yields as depicted in Scheme 19. As mentioned above, not only triflic anhydride, but various Lewis acids (TMSOTf, Sn

[3 + 2]-Cycloaddition reaction of sydnones with alkynes

• Veronika Hladíková,
• Jiří Váňa and
• Jiří Hanusek

Beilstein J. Org. Chem. 2018, 14, 1317–1348, doi:10.3762/bjoc.14.113

• the catalytic efficiency. Gomez-Bengoa and Harrity et al. [92] also inspected the role of Cu(I)/Cu(II) salts as well as other Lewis acids which could strengthen the electrophilicity of the starting sydnone under thermal reaction conditions. They found two competitive catalytic routes leading to

• different cycloaddition products. According to their original presumption some Lewis acids (TMSOTf < Zn(OAc)2 < MgBr2 < Cu(OTf)2) catalyzed the thermal reaction of phenylsydnone with phenylacetylene to give the expected 1,3-diphenylpyrazole in a ratio >10:1 over the 1,4-diphenyl isomer. Quantum calculations

• ). A completely different ratio of both isomers was observed when Cu(II) carboxylates and acetylacetonates were employed instead of Cu(OTf)2. This was explained by different operating mechanisms. While Cu(OTf)2, Cu(TFA)2 and Cu(BF4)2 behave mainly as Lewis acids, other Cu(II) salts/complexes

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