Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6

• formed as the major reaction products depending on the nature of the substituents and the Lewis acid (Scheme 27, Table 9) [257]. The reaction of trialkylsilylperoxyacetals with alkenes in the presence of Lewis acids also proceeds through the formation of peroxycarbenium ions. For example, the reaction of

An efficient method for the construction of polysubstituted 4-pyridones via self-condensation of β-keto amides mediated by P₂O₅ and catalyzed by zinc bromide

• Liquan Tan,
• Peng Zhou,
• Cui Chen and
• Weibing Liu

Beilstein J. Org. Chem. 2013, 9, 2681–2687, doi:10.3762/bjoc.9.304

• conditions (Scheme 5). We were astonished to find that the results only included the self-condensation products (2a, 2l, 2j) and achieved not the cross-condensation products. It is well known that Lewis acids can activate β-keto amides [32]. Under mild conditions, phosphorus pentoxide (P2O5) is often used as

Garner’s aldehyde as a versatile intermediate in the synthesis of enantiopure natural products

• Mikko Passiniemi and
• Ari M.P. Koskinen

Beilstein J. Org. Chem. 2013, 9, 2641–2659, doi:10.3762/bjoc.9.300

• in the presence of 100 mol % of TiCl4 in THF gave a 5:1 (anti/syn) mixture of adducts 20 and 21. Tetrahydrofuran coordinates quite strongly to Lewis acids, which increases the electron density at the metal atom. This lowers the metal atom’s ability to coordinate to other Lewis bases, such as the

• that of Al, the low reactivity of organylzirconocene chlorides towards carbonyl compounds is puzzling. It is likely that the presence of two sterically demanding cyclopentadienyl (Cp) groups is at least partially responsible for their low reactivity. Suzuki noticed that Lewis acids promote C–C-bond

• enough to inverse the selectivity (Table 1, entries 10, 11, 16 and 17). Less coordinating solvents, such as toluene or CH2Cl2 can also affect the selectivity. A greater effect on the selectivity can be reached by the addition of Lewis acids. Usually Zn(II)-salts give fair to good syn-selectivities (Table

New developments in gold-catalyzed manipulation of inactivated alkenes

• Michel Chiarucci and
• Marco Bandini

Beilstein J. Org. Chem. 2013, 9, 2586–2614, doi:10.3762/bjoc.9.294

• deuterated compounds 14a,b permitted to confirm the anti-diastereoselective hydroamination of the double bond. (Scheme 5b). Interestingly, although 14 represents a likely intermediate of the reaction course, when it was treated with various Brønsted and Lewis acids, the expected product 16 was not observed

Ambient gold-catalyzed O-vinylation of cyclic 1,3-diketone: A vinyl ether synthesis

• Yumeng Xi,
• Boliang Dong and
• Xiaodong Shi

Beilstein J. Org. Chem. 2013, 9, 2537–2543, doi:10.3762/bjoc.9.288

• selectivity for the diketone addition over hydration was maintained as shown in Table 1. Solvent screening shown in Scheme 2 proved that the trace amount of acid from chloroform decomposition was crucial for the optimal performance, which likely helped the protodeauration. Other Lewis acids have also been

Synthetic scope and DFT analysis of the chiral binap–gold(I) complex-catalyzed 1,3-dipolar cycloaddition of azlactones with alkenes

• María Martín-Rodríguez,
• Luis M. Castelló,
• Carmen Nájera,
• José M. Sansano,
• Olatz Larrañaga,
• Abel de Cózar and
• Fernando P. Cossío

Beilstein J. Org. Chem. 2013, 9, 2422–2433, doi:10.3762/bjoc.9.280

• oxazolone 5aa and NPM catalyzed by [(Sa)-Binap-AuTFA]2. In previous works, we have demonstrated that the stereoselectivity of the 1,3-DC employing chiral metallic Lewis acids arises from the blockage of one of the prochiral faces [34]. Starting from this selected conformation of the catalyst, our results

Synthesis of mucin-type O-glycan probes as aminopropyl glycosides

• David Benito-Alifonso,
• Rachel A. Jones,
• Anh-Tuan Tran,
• Hannah Woodward,
• Nichola Smith and
• M. Carmen Galan

Beilstein J. Org. Chem. 2013, 9, 1867–1872, doi:10.3762/bjoc.9.218

• and acceptors that both have a free hydroxy group [27]. In this report, we employed the difference in reactivity of trichloroacetimidates and thioglycoside donors. In general, trichloroacetimidates are activated by strong Lewis acids such as TMSOTf [28], while the more stable thioglycosides require

Gold(I)-catalyzed formation of furans from γ-acyloxyalkynyl ketones

• Marie Hoffmann,
• Solène Miaskiewicz,
• Jean-Marc Weibel,
• Patrick Pale and
• Aurélien Blanc

Beilstein J. Org. Chem. 2013, 9, 1774–1780, doi:10.3762/bjoc.9.206

• ability of gold cations to act as π or σ Lewis acids (Scheme 3) [21][55][56]. Intramolecular [1,4]-addition of the acyloxy function by oxophilic activation of γ-acyloxyalkynyl ketones could lead to the formation of gold allenolate A, which is in equilibrium with both Z or E vinylgold B and C [57

Zinc–gold cooperative catalysis for the direct alkynylation of benzofurans

• Yifan Li and
• Jérôme Waser

Beilstein J. Org. Chem. 2013, 9, 1763–1767, doi:10.3762/bjoc.9.204

• (OTf)2 in catalytic amount led to a lower yield (Table 1, entry 9), and a larger excess resulted in decomposition of the starting material only (Table 1, entry 10). Although other Lewis acids could also be used (Table 1, entries 11 and 12) [29], no better results than with Zn(OTf)2 were obtained (Table

Synthesis of the reported structure of piperazirum using a nitro-Mannich reaction as the key stereochemical determining step

• James C. Anderson,
• Andreas S. Kalogirou,
• Michael J. Porter and
• Graham J. Tizzard

Beilstein J. Org. Chem. 2013, 9, 1737–1744, doi:10.3762/bjoc.9.200

• . Enantioselective reactions have been controlled by asymmetric metal-centred Lewis acids; chiral hydrogen bond donors, in particular by the use of asymmetric thiourea organocatalysts, chiral Brønsted acids, phase-transfer catalysts and Brønsted base catalysts [3][15][25][26][27][28][29][30][31][32][33][34][35][36

Gallium-containing polymer brush film as efficient supported Lewis acid catalyst in a glass microreactor

• Rajesh Munirathinam,
• Roberto Ricciardi,
• Richard J. M. Egberink,
• Jurriaan Huskens,
• Michael Holtkamp,
• Herbert Wormeester,
• Uwe Karst and
• Willem Verboom

Beilstein J. Org. Chem. 2013, 9, 1698–1704, doi:10.3762/bjoc.9.194

• sulfonate groups of the PSS polymer brushes was incorporated. Upon slow deactivation the catalytic activity of the microreactor can be easily reactivated to its initial value by flowing through a solution of GaCl3. We believe that this approach has a wider scope and can be used to anchor other Lewis acids

Organocatalyzed enantioselective desymmetrization of aziridines and epoxides

• Ping-An Wang

Beilstein J. Org. Chem. 2013, 9, 1677–1695, doi:10.3762/bjoc.9.192

• -aziridines and meso-epoxides by metal-based Lewis acids cooperating with chiral ligands has been well established [16][17][18][19][20][21][22][23][24][25][26][27][28]. However, the enantioselective desymmetrization of meso-aziridines and meso-epoxides catalyzed by small chiral organic molecules has only

A Lewis acid-promoted Pinner reaction

• Dominik Pfaff,
• Gregor Nemecek and
• Joachim Podlech

Beilstein J. Org. Chem. 2013, 9, 1572–1577, doi:10.3762/bjoc.9.179

• esters; Lewis acids; Pinner reaction; Ritter reaction; Introduction In 1877 Pinner and Klein discovered the proton-induced imidate syntheses [1][2]. They passed anhydrous gaseous hydrogen chloride through a mixture of isobutyl alcohol and benzonitrile. A crystalline product precipitated, which they

•  1, entries 2 and 3). The 3% yield in acetonitrile/water (10:1) suggests that water is detrimental in the Pinner reaction. Among various tested Lewis acids, the best results were obtained with aluminium tribromide at 50 °C (65%, Table 1, entry 5) and with trimethylsilyl triflate at room temperature

True and masked three-coordinate T-shaped platinum(II) intermediates

• Manuel A. Ortuño,
• Salvador Conejero and
• Agustí Lledós

Beilstein J. Org. Chem. 2013, 9, 1352–1382, doi:10.3762/bjoc.9.153

• * and IMes hampering the approach of the CH bond to the metal center. Once again, Lewis acids as acetonitrile can access the empty site, which means that a potential reactant molecule can coordinate to the metal for further reactions. Masked T-shaped via agostic interaction The agostic interaction [29

• generated [41] by methide abstraction from the neutral derivative cis-[Pt(Me)2(PiPr3)2] by using highly electrophilic Lewis acids such as B(C6F5)3 or [CPh3][1-H-closo-CB11Me11] (with the concomitant formation of MeB(C6F5)3− or MeCPh3, respectively). This synthetic route uses the same procedure described by

Mild and efficient cyanuric chloride catalyzed Pictet–Spengler reaction

• Ashish Sharma,
• Mrityunjay Singh,
• Nitya Nand Rai and
• Devesh Sawant

Beilstein J. Org. Chem. 2013, 9, 1235–1242, doi:10.3762/bjoc.9.140

• Brønsted acids. However, recently several other aprotic or Lewis acids, such as Yb(OTf)3 [23][24][25], AuCl3/AgOTf [26], Me3SiCl [27][28], BF3·Et2O [29], iodine [30], zeolite [31] and enzymes [32][33][34], have been used for carrying out the Pictet–Spengler reaction. Though the Pictet–Spengler reaction has

Conformational analysis and intramolecular interactions in monosubstituted phenylboranes and phenylboronic acids

• Josué M. Silla,
• Rodrigo A. Cormanich,
• Roberto Rittner and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2013, 9, 1127–1134, doi:10.3762/bjoc.9.125

• , in addition to typical intramolecular hydrogen bonds [7]. Niedenzu [8] presented studies in organic synthesis with evidence of intramolecular interactions between boron and electronegative atoms such as F, Cl, O, N and S. Indeed, boron-containing compounds are Lewis acids, because of the empty p

Reductions of aldehydes and ketones with a readily available N-heterocyclic carbene borane and acetic acid

• Vladimir Lamm,
• Xiangcheng Pan,
• Tsuyoshi Taniguchi and
• Dennis P. Curran

Beilstein J. Org. Chem. 2013, 9, 675–680, doi:10.3762/bjoc.9.76

• easily to release reactive borane (BH3) to solution under typical thermal reaction conditions. Perhaps because of their stability, the potential use of carbene-boranes as hydride sources has been largely overlooked. Lindsay and McArthur reported that strong Lewis acids such as BF3 and Sc(OTf)3 activate

Asymmetric synthesis of a highly functionalized bicyclo[3.2.2]nonene derivative

• Toshiki Tabuchi,
• Daisuke Urabe and
• Masayuki Inoue

Beilstein J. Org. Chem. 2013, 9, 655–663, doi:10.3762/bjoc.9.74

• selective activation of acrolein in the presence of the Lewis-basic allylic oxygen was a prerequisite to the successful formation of 8. We anticipated that bulky trialkylsilyl triflates would function as such chemoselective Lewis acids, because the activation of the TBS-connected oxygen of 7 by the silyl

A new intermediate in the Prins reaction

• Shinichi Yamabe,
• Takeshi Fukuda and
• Shoko Yamazaki

Beilstein J. Org. Chem. 2013, 9, 476–485, doi:10.3762/bjoc.9.51

• Lewis acids are employed to catalyze the reaction, and Prins-type reactions have found numerous synthetic applications [6][19][20][21][22][23][24][25]. In spite of the extensive experimental studies, there have been no computational studies of the classic Prins reaction. The reaction is also important

Metal-mediated aminocatalysis provides mild conditions: Enantioselective Michael addition mediated by primary amino catalysts and alkali-metal ions

• Matthias Leven,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2013, 9, 155–165, doi:10.3762/bjoc.9.18

• catalysis provides an effective alternative to conventional primary amino catalysis were strong acid additives are essential components. Keywords: alkali metals; aminocatalysis; DFT-calculations; Lewis acids; Michael addition; Introduction Organocatalysis based on primary or secondary amines enables a

• ][13]. In most cases, transition or rare-earth metals are employed as Lewis acids in order to activate electrophilic compounds to react with substrates that are directly bonded to an organic catalyst [9][10][11][12][13]. An example is the enamine–metal Lewis acid bifunctional catalysis for asymmetric

• -hydroxycoumarin (1) to prochiral α,β-unsaturated ketones. Instead of acid additives, which sometimes lead to decomposition of sensitive components [18], alkali-metal ions are employed as very mild Lewis acids (Scheme 1). The activation of Michael acceptors by iminium ions enables asymmetric additions of 4

Removal of benzylidene acetal and benzyl ether in carbohydrate derivatives using triethylsilane and Pd/C

• Abhishek Santra,
• Tamashree Ghosh and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2013, 9, 74–78, doi:10.3762/bjoc.9.9

• reported for the removal of benzylidene acetals by using strong protic and Lewis acids [10][11][15] as well as some heterogeneous acidic catalysts [16][17]. Removal of benzylidene acetal under nonacidic conditions includes hydrogenolysis using hydrogen gas over Pd/C [18], or treatment with hydrazine [19

A new approach toward the total synthesis of (+)-batzellaside B

• Jolanta Wierzejska,
• Shin-ichi Motogoe,
• Yuto Makino,
• Tetsuya Sengoku,
• Masaki Takahashi and
• Hidemi Yoda

Beilstein J. Org. Chem. 2012, 8, 1831–1838, doi:10.3762/bjoc.8.210

• exemplified by performing the procedures with AllylTMS and two types of Lewis acids, which allows for simpler synthetic operation due to the ease of purification of the products. The present study clearly demonstrates that L-pyroglutamic acid can be used as a versatile chiral source for synthesizing this

Asymmetric Brønsted acid-catalyzed aza-Diels–Alder reaction of cyclic C-acylimines with cyclopentadiene

• Magnus Rueping and
• Sadiya Raja

Beilstein J. Org. Chem. 2012, 8, 1819–1824, doi:10.3762/bjoc.8.208

• chiral Lewis acids [5][6][7][8][9][10][11][12][13][14][15][16]. Recently, chiral Brønsted acids have attracted interest as effective catalysts for a variety of asymmetric transformations involving imine electrophiles [17][18][19][20][21][22][23]. Among others, the aza-Diels–Alder reaction of imino

Imidazolinium and amidinium salts as Lewis acid organocatalysts

• Oksana Sereda,
• Nicole Clemens,
• Tatjana Heckel and
• René Wilhelm

Beilstein J. Org. Chem. 2012, 8, 1798–1803, doi:10.3762/bjoc.8.205

• desulfurization of the products containing a thiol or thiocarbonyl group. Keywords: Diels–Alder; ionic liquids; organocatalysis; soft Lewis acids; thiiranes; thioesters; Introduction Salts with melting points below 100 °C are known as ionic liquids and are often used as novel solvents for reactions and

• hydrogen-bond activation catalysts [18]. The utilization of the soft Lewis basic sulfur groups in this reaction is rare. Often mercury Lewis acids are applied [19][20][21][22] to activate the sulfur group and there is also the risk of desulfurization [23]. The only known asymmetric Diels–Alder reaction

• ) was performed in different solvents, at varied temperatures, by using a broad range of catalysts, which are summarized in Table 1. First a few metal-based Lewis acids were applied in the reaction. BF3•Et2O is known to activate also sulfur carbonyl groups [24] and gave the product in 90% yield, while

Metal–ligand multiple bonds as frustrated Lewis pairs for C–H functionalization

• Matthew T. Whited

Beilstein J. Org. Chem. 2012, 8, 1554–1563, doi:10.3762/bjoc.8.177

• number of unsaturated main-group compounds can exhibit electronic properties and reactivity reminiscent of transition metals [3]. A different approach was pioneered by Stephan, who demonstrated that appropriately encumbered (i.e., "frustrated") Lewis acids and bases could achieve synergistic heterolytic

• have extended the approach to include transition metals as Lewis acids and bases [7][8]. In this review, we show that the FLP concept may be extended to encompass certain metal–ligand multiply bonded species, provided that the metal retains an open coordination site to facilitate cooperative reactivity

• analogues of the recently developed frustrated Lewis pairs involving main-group Lewis acids and bases. Although the manner in which "frustration" occurs is somewhat different (i.e., it is primarily electronic and not steric in origin), the types of reactivity observed are remarkably similar. One example in