The McKenna reaction – avoiding side reactions in phosphonate deprotection

• Katarzyna Justyna,
• Joanna Małolepsza,
• Damian Kusy,
• Waldemar Maniukiewicz and
• Katarzyna M. Błażewska

Beilstein J. Org. Chem. 2020, 16, 1436–1446, doi:10.3762/bjoc.16.119

• . Since the known procedures for the syntheses of oxazoles are rather harsh and usually involve higher temperature [Pd(OAc)2, toluene, AcOH, 100 °C, 24 h [41] and/or the presence of Lewis acids (FeCl3, ACN (24 h, 80 °C) or 1,2-DCE (2 h, 80 °C), DCM (24 h, 45 °C) [40]], we envisioned that the present

Copper-catalyzed enantioselective conjugate addition of organometallic reagents to challenging Michael acceptors

• Delphine Pichon,
• Jennifer Morvan,
• Christophe Crévisy and
• Marc Mauduit

Beilstein J. Org. Chem. 2020, 16, 212–232, doi:10.3762/bjoc.16.24

• acylimidazole Michael acceptors, the first use of α,β-unsaturated N-acyloxazolidinones was also described in asymmetric Friedel–Crafts 1,4-additions catalyzed by chiral copper/bisoxazolidine Lewis acids [42][43][44][45][46]. Thanks to the easy post-transformation of the oxazolidine moiety, the resulting

Efficient method for propargylation of aldehydes promoted by allenylboron compounds under microwave irradiation

• Jucleiton J. R. Freitas,
• Queila P. S. B. Freitas,
• Silvia R. C. P. Andrade,
• Juliano C. R. Freitas,
• Roberta A. Oliveira and
• Paulo H. Menezes

Beilstein J. Org. Chem. 2020, 16, 168–174, doi:10.3762/bjoc.16.19

• ] or boron [26][27][28] to perform propargylation reactions typically requires catalysis by Lewis acids or bases and although the utility of allenylstannanes is further indicated by the commercial availability of some of them, the toxicity of these compounds makes them inappropriate for the use in

[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

• control experiments and DFT calculations. Keywords: Brønsted and Lewis acids; DFT; mechanistic studies; rearrangement; stereochemistry; sulfur atom migration; Introduction Among all organic reactions, rearrangements are an exciting class of transformations where unusual or even unexpected products can

• -hydroxyalkylphosphine sulfides, and therefore, an alternative methodology had to be developed for the synthesis of chiral organophosphorus compounds possessing either phosphaindane or benzophosphorinane skeletons. As such, it was decided to test the ability of Lewis acids to catalyze the cyclization of β

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

• in the presence of acetic anhydride. Among the various Lewis acids tested, the desired acetolysis products were obtained in moderate yields under tin(IV) chloride catalysis. Our methodology could be extended to regioselective protecting group installations and manipulations towards a number of

• backbone of Neu5Ac. Thus, the aim of this study was to cleave the ring of the 2,7-anhydro derivatives with a choice of suitable Lewis acids as catalysts in order to utilize the acetolysis products as building blocks for the chemical synthesis of Neu5Ac-containing glycans. Results and Discussion It is known

• crystallography, compounds 2 and 3 were acetylated with Ac2O in the presence of a catalytic amount of 4-(dimethylamino)pyridine (DMAP) in pyridine to give 5 [6] and 6 in 75 and 77% yield, respectively (Scheme 1), and the compatibility of acetyl protecting groups with the Lewis acids during acetolysis reactions

Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?

• Dominika Krištofíková,
• Juraj Filo,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290

• as trialkylsilyl triflates [18][19]. The rearrangement of ester enolates generated by LDA with metal ions bearing bulky cyclopentadienyl ligands proceeded well with yields of up to 90%, and diastereomeric ratios strongly depended on the ligands used [20]. The presence of catalytic amounts of Lewis

• acids improved the diastereoselectivity and the reaction rate of silyl ketene acetals of (E)-allylic esters [21]. Chiral bromoboranes were used to form boranyl ketene acetals from ester enolates generated from allyl esters with tertiary amines. The geometry of the enolates depended strongly on the

Synthetic terpenoids in the world of fragrances: Iso E Super^® is the showcase

• Alexey Stepanyuk and
• Andreas Kirschning

Beilstein J. Org. Chem. 2019, 15, 2590–2602, doi:10.3762/bjoc.15.252

• . investigated the influence of Brønstedt and Lewis acids on the formation of Georgywood® (35). It was found that Lewis acids such as AlCl3 shift the equilibrium towards Georgywood® (35) type products especially when employed in over-stoichiometric amounts. Using different Brønstedt acids, the ratios between the

Reactions of 2-carbonyl- and 2-hydroxy(or methoxy)alkyl-substituted benzimidazoles with arenes in the superacid CF₃SO₃H. NMR and DFT studies of dicationic electrophilic species

• Dmitry S. Ryabukhin,
• Alexey N. Turdakov,
• Natalia S. Soldatova,
• Mikhail O. Kompanets,
• Alexander Yu. Ivanov,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1962–1973, doi:10.3762/bjoc.15.191

• (Figure 3) with arenes under the action of Brønsted (super)acids CF3SO3H (TfOH, triflic acid), H2SO4 and strong Lewis acids AlX3 (X = Cl, Br). One would expect the electrophilic activation of carbonyl or 2-hydroxyalkyl groups of these benzimidazoles in hydroxyalkylation and alkylation of arenes. Results

• –8 with arenes under the action of Brønsted acids (H2SO4, TfOH) or Lewis acids (AlX3, X = Cl, Br). Reactions of 2-formyl-1-methylbenzimidazole (1) with various arenes (benzene, and its methyl, methoxy or chloro-substituted derivatives) are given in Table 3. These reactions proceed on the formyl group

• reaction products 12a–h, 13, and 14 was achieved. No reactions took place at lower temperature or under the action of Lewis acids AlX3 (X = Cl, Br). For these 2-hydroxyalkylbenzimidazoles 3a–c, 4, 7, and 8, we were able to receive compounds 12–14 only in reactions with benzene, 1,2-dichlorobenzene and 1,3

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

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

• (Scheme 30) [118]. Reaction optimization has shown Cu(OAc)2 to be suitable for this transformation whereas other Lewis acids like CuI, Cu(OTf)2 and FeCl3 gave lower yields, whereas Zn(OAc)2 did not result in any product. The strategy has well tolerated different substituents on pyridine and benzylamine as

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

• facilitating this reaction has been extended to include other Brønsted and Lewis acids, such as phosphomolybdic acid (PMA) [24], Ca(NTf2)2 [25], In(OTf)3 [26], La(OTf)3 [27], and BF3·OEt2 [28], as well as other nucleophiles [29][30][31]. In all cases examined, the products of the aza-Piancatelli reaction have

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