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

Reactions of N,3-diarylpropiolamides with arenes under superelectrophilic activation: synthesis of 4,4-diaryl-3,4-dihydroquinolin-2(1H)-ones and their derivatives

• Larisa Yu. Gurskaya,
• Diana S. Belyanskaya,
• Dmitry S. Ryabukhin,
• Denis I. Nilov,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2016, 12, 950–956, doi:10.3762/bjoc.12.93

• )-ones [12][13]. The main goal of this work was a systematic study on reactions of 3-aryl-N-(aryl)propiolamides with arenes under the action of the Brønsted superacid TfOH (CF3SO3H, triflic acid), strong Lewis acids AlX3 (X = Cl, Br), or the conjugate Brønsted–Lewis superacid TfOH–SbF5. Results and

• Discussion The protonation of alkynamides 1 on both the oxygen atom of the amide group and a carbon atom of the acetylene bond in superacids or coordination of these basic centers with strong Lewis acids leads to the formation of dications A that are considered as superelectrophiles [15] (Scheme 1). These

A practical way to synthesize chiral fluoro-containing polyhydro-2H-chromenes from monoterpenoids

• Oksana S. Mikhalchenko,
• Dina V. Korchagina,
• Konstantin P. Volcho and
• Nariman F. Salakhutdinov

Beilstein J. Org. Chem. 2016, 12, 648–653, doi:10.3762/bjoc.12.64

• appropriate halogen-containing Lewis acids or ionic liquids are usually used (Scheme 2) [10][11][12][13][14][15][16]. However, only a few examples of reactions for introducing a fluorine atom via the halo-Prins cyclization have been reported to date [15][16][17][18][19][20][21]. In these reactions, BF3·Et2O

Copper-mediated arylation with arylboronic acids: Facile and modular synthesis of triarylmethanes

• H. Surya Prakash Rao and
• A. Veera Bhadra Rao

Beilstein J. Org. Chem. 2016, 12, 496–504, doi:10.3762/bjoc.12.49

• ) delivered the desired triphenylmethane (11a) in good yield (78%) after chromatographic purification. We screened other borderline Lewis acids such as Sc(OTf)3, Yb(OTf)3, Zn(OTf)2 and Fe(OTf)3, but the reaction did not afford triphenylmethane (11a) at all, which indicated that Cu(II) and not TfOH is

Diastereoselective Ugi reaction of chiral 1,3-aminoalcohols derived from an organocatalytic Mannich reaction

• Samantha Caputo,
• Andrea Basso,
• Lisa Moni,
• Renata Riva,
• Valeria Rocca and
• Luca Banfi

Beilstein J. Org. Chem. 2016, 12, 139–143, doi:10.3762/bjoc.12.15

• moderate diastereoselectivity was achieved (Table 1, entry 1), which could be increased by changing the solvent to trifluoroethanol, especially effective at 0 °C. Considering the recent work by Nenajdenko et al. [17], we explored the usage of Lewis acids in an aprotic solvent in order to further improve

• . Other zinc-based catalysts were less efficient, whereas most of the other tested Lewis acids failed to promote the reaction at all. The use of Lewis acids in methanol or trifluoroethanol afforded lower yields with no improvement of diastereoselection. It is worth noting that a 10:1 diastereoselectivity

Beyond catalyst deactivation: cross-metathesis involving olefins containing N-heteroaromatics

• Kevin Lafaye,
• Cyril Bosset,
• Lionel Nicolas,
• Amandine Guérinot and
• Janine Cossy

Beilstein J. Org. Chem. 2015, 11, 2223–2241, doi:10.3762/bjoc.11.241

• that can be formed from the corresponding amines either in a preliminary step or in situ, in the presence of an acidic additive [30][31][32][33][34][35]. In addition, Lewis acids in catalytic amounts were shown to enhance the reactivity of amino compounds in metathesis reactions [36][37]. Involvement

Synthesis of constrained analogues of tryptophan

• Elisabetta Rossi,
• Valentina Pirovano,
• Marco Negrato,
• Giorgio Abbiati and
• Monica Dell’Acqua

Beilstein J. Org. Chem. 2015, 11, 1997–2006, doi:10.3762/bjoc.11.216

• results are summarized in Table 1. The reaction was ineffective under thermal conditions (Table 1, entry 1). As a consequence we tested simple Lewis acids as potential promoters for the transformation. Magnesium perchlorate, scandium and copper triflate and boron trifluoride failed to give the desired

• Lewis acid, only EtAlCl2 is able to trigger the reaction toward the formation of the desired cycloadducts 3/3'. Similarly, Piersanti and co-workers reported the unique capability of EtAlCl2, with respect to related hard Lewis acids, to activate 2 toward the nucleophilic addition of indoles [29]. They

Aerobic addition of secondary phosphine oxides to vinyl sulfides: a shortcut to 1-hydroxy-2-(organosulfanyl)ethyl(diorganyl)phosphine oxides

• Svetlana F. Malysheva,
• Alexander V. Artem’ev,
• Nina K. Gusarova,
• Nataliya A. Belogorlova,
• Alexander I. Albanov,
• C. W. Liu and
• Boris A. Trofimov

Beilstein J. Org. Chem. 2015, 11, 1985–1990, doi:10.3762/bjoc.11.214

• approaches to construct new C–P bonds, that provide straightforward access to tertiary phosphines and their chalcogenides [8][9][10][11][12]. Conventionally, the activation of the P–H bonds in this reaction is achieved by using radical initiators [13][14][15], Brønsted/Lewis acids [16][17] and bases [18][19

Lewis acid-promoted hydrofluorination of alkynyl sulfides to generate α-fluorovinyl thioethers

• Davide Bello and
• David O'Hagan

Beilstein J. Org. Chem. 2015, 11, 1902–1909, doi:10.3762/bjoc.11.205

• thioester enols and enolates, important intermediates in enzymatic C–C bond forming reactions. The method opens access to appropriate analogues for investigations in this direction. Keywords: alkynyl sulfides; α-fluorovinyl thioethers; hydrofluorination; Lewis acids; organofluorine; Introduction

• obtained as a 4:1 mixture of Z/E-isomers, and they could only be isolated in a modest yield (35%) as shown in Scheme 2 and Table 1 (entry 7). Encouraged by this result, a number of Lewis acids were tested, including SnCl2, ZnCl2, Sc(OTf)3, AuCl·SMe2 and B(C6F5)3 (Table 1). The Lewis acids (1.5 equivalents

• group, possibly with its participation in the reaction process. 19F NMR was used to probe changes in the Lewis acids in the reaction. Ratios of 1:2 Lewis acid:3HF·Et3N mixtures in CD2Cl2 were stirred at room temperature for 2 hours, and the aliquots (0.7 mL) were assayed in Teflon NMR tubes. 19F NMR

Tandem cross enyne metathesis (CEYM)–intramolecular Diels–Alder reaction (IMDAR). An easy entry to linear bicyclic scaffolds

• Javier Miró,
• María Sánchez-Roselló,
• Álvaro Sanz,
• Fernando Rabasa,
• Carlos del Pozo and
• Santos Fustero

Beilstein J. Org. Chem. 2015, 11, 1486–1493, doi:10.3762/bjoc.11.161

• tandem process (Table 1, entries 9 and 10). The use of Lewis acids as co-catalysts was also tested although the efficiency of the process did not improve neither with Ti(OiPr)4 nor with BF3·OEt2 (Table 1, entries 11 and 12). Alternatively, thiourea derivatives have proven to be very effective hydrogen

Diastereoselective and enantioselective conjugate addition reactions utilizing α,β-unsaturated amides and lactams

• Katherine M. Byrd

Beilstein J. Org. Chem. 2015, 11, 530–562, doi:10.3762/bjoc.11.60

• This section will focus on Lewis acid-catalyzed ECA reactions, which employ stabilized nucleophiles such as silyl enol ethers and amines. Chiral Lewis acids play a dual role in these reactions. They activate the Michael acceptors by coordinating with the carbonyl oxygen and they provide a chiral

Selective methylation of kaempferol via benzylation and deacetylation of kaempferol acetates

• Qinggang Mei,
• Chun Wang,
• Weicheng Yuan and
• Guolin Zhang

Beilstein J. Org. Chem. 2015, 11, 288–293, doi:10.3762/bjoc.11.33

• and then hydrolysis in 1 M HCl (aq) at room temperature was an excellent method for selective removal of the 3- and 5-O-acetyl groups from triacetylated kaempferol (2). No side products were detected by TLC analysis. With other Lewis acids such as ZnCl2, the result was very different. The desired

Cross-dehydrogenative coupling for the intermolecular C–O bond formation

• Igor B. Krylov,
• Vera A. Vil’ and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2015, 11, 92–146, doi:10.3762/bjoc.11.13

• in a basic medium [173]. The oxidative esterification of aldehydes was performed using peroxides in the presence of Lewis acids or in the absence of the latter; for example, using oxone in the presence of In(OTf)3 [174][175], oxone [174][176], Caro’s acid [177], H2O2aq (30%) in the presence of CaCl2

Efficient deprotection of F-BODIPY derivatives: removal of BF₂ using Brønsted acids

• Mingfeng Yu,
• Joseph K.-H. Wong,
• Cyril Tang,
• Peter Turner,
• Matthew H. Todd and
• Peter J. Rutledge

Beilstein J. Org. Chem. 2015, 11, 37–41, doi:10.3762/bjoc.11.6

• recent reports have deployed Lewis acids to achieve this transformation: Thompson and co-workers used boron trihalides in dichloromethane under anhydrous conditions, followed by treatment with acetone/water (10:1) to achieve quantitative removal of the BF2 moiety [18]; Ravikanth and co-workers screened a

• range of metal-based Lewis acids (ZrCl4, TiCl4, AlCl3, Sc(OTf)3, SnCl4) and reported yields up to 96% using ZrCl4 in refluxing methanol/acetonitrile [19]. Related efforts have wrought substitution at boron in F-BODIPY analogues without removing it from the dipyrrin. For example, Lundrigan et al. have

• organic acid TFA or the inorganic acid HCl. These conditions are complementary to those previously reported for converting F-BODIPYs to the parent dipyrrins using either strong bases or Lewis acids. Compared to existing methods, the Brønsted acid conditions are relatively mild and operationally simple

Lewis acid-catalyzed redox-neutral amination of 2-(3-pyrroline-1-yl)benzaldehydes via intramolecular [1,5]-hydride shift/isomerization reaction

• Chun-Huan Jiang,
• Xiantao Lei,
• Le Zhen,
• Hong-Jin Du,
• Xiaoan Wen,
• Qing-Long Xu and
• Hongbin Sun

Beilstein J. Org. Chem. 2014, 10, 2892–2896, doi:10.3762/bjoc.10.306

• for 24 h gave the trisubstituted amine 3a in 50% yield (entry 1, Table 1). Encouraged by this result, we screened readily available Brønsted and Lewis acids (Table 1). Except the Lewis acid AlCl3, other strong Brønsted acids and common Lewis acids could be used as the catalyst in this reaction

A general metal-free approach for the stereoselective synthesis of C-glycals from unactivated alkynes

• Shekaraiah Devari,
• Manjeet Kumar,
• Ramesh Deshidi,
• Masood Rizvi and
• Bhahwal Ali Shah

Beilstein J. Org. Chem. 2014, 10, 2649–2653, doi:10.3762/bjoc.10.277

• these methods use priorly activated terminal alkynes, e.g., silylacetylene, activated with various Lewis acids such as SnCl4, BF3·OEt2, TiCl4, I2, InBr3, and ZrCl4 [24][25][26][27][28][29][30], followed by a Ferrier type rearrangement [31][32][33][34] (Scheme 1). A consequence of the prior activation of

• challenge. We reasoned that the development of a strategy which in situ activates the terminal alkyne and further catalyzes the reaction without the aid of other Lewis acids might be a solution to this problem. Thus, in continuation of our efforts [36][37][38], we describe a highly stereoselective TMSOTf