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

• catalytic (R)-3,3’-dibromo-BINOL (16) and stoichiometric SnCl4 [19] (Scheme 4). The authors proposed that complex 18 acted as a chiral proton source to protonate a tin-enolate intermediate based upon related complexes that the Yamamoto group had previously used for the enantioselective protonation of silyl

• enol ethers [20][21]. Electron-rich and neutral indoles were efficient substrates for the reaction; however, electron-poor indoles showed attenuated reactivity even when 1.6 equivalents of SnCl4 were employed (60–63% yield, 96:4 to 96.5:3.5 er). Indoles lacking substitution at the 2-position (R1 = H

A selective and mild glycosylation method of natural phenolic alcohols

• Mária Mastihubová and
• Monika Poláková

Beilstein J. Org. Chem. 2016, 12, 524–530, doi:10.3762/bjoc.12.51

• promoted by a Lewis acid (SnCl4) in DCM failed. The deacetylated aglycone – vanillyl alcohol along with some amounts of 2,3,4,6-tetra-O-acetyl-D-glucopyranose were isolated. It is evident that these frequently used reaction conditions require more acid-stable derivatives. Therefore, it was reasonable to

Study on the synthesis of the cyclopenta[f]indole core of raputindole A

• Nils Marsch,
• Mario Kock and
• Thomas Lindel

Beilstein J. Org. Chem. 2016, 12, 334–342, doi:10.3762/bjoc.12.36

• were 6-hydroxyallylated indolines which gave good yields of cyclopenta[f]indolines after treatment with SnCl4, as soon as sterically demanding β-cyclocitral adducts were reacted. Most successful were Pt(II) and Au(I)-catalyzed cyclizations of N-TIPS-protected indolin-6-yl-substituted propargylacetates

• of cyclopentene anellation by cyclization of aryl-substituted allyl cations. High yields were reported by Alvarez-Manzaneda et al. in the course of their total synthesis of taiwaniaquinone H. They induced the cyclization by treatment of arylvinylcarbinols with the mild Lewis acid SnCl4, which were

• synthesized by hydroxyalkylation with β-cyclocitral [46]. Hydroxyalkylation of Boc-protected 6-iodoindole (3) with 6-β-cyclocitral (30) was possible after iodine/magnesium exchange, affording adduct 31 (Scheme 5). However, treatment of 31 with SnCl4 in DCM did not afford any defined product. This changed

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

• 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

A carbohydrate approach for the formal total synthesis of (−)-aspergillide C

• Pabbaraja Srihari,
• Namballa Hari Krishna,
• Ydhyam Sridhar and
• Ahmed Kamal

Beilstein J. Org. Chem. 2014, 10, 3122–3126, doi:10.3762/bjoc.10.329

• benzoyl chloride in the presence of pyridine to produce the corresponding benzoyl ester 7 as a side chain fragment to be utilized for a Ferrier-type C-glycosylation reaction with the sugar tri-O-acetyl-D-galactal (6). Compound 6 was treated with silylated alkyne 7 in the presence of SnCl4 to afford

• . Synthesis of 11. Reaction conditions: (a) n-BuLi, THF/HMPA (5:1), −78 °C to rt, 12 h, 95%; (b) Li, t-BuOK, H2N(CH2)3NH2, rt, 4 h, 92%; (c) i. n-BuLi, TMSCl, THF, −78 °C, 92%. ii. pyridine, C6H5COCl, CH2Cl2, 0 °C to rt, 1 h, 98%; (d) SnCl4, CH2Cl2, 0 °C to rt, 1 h, 85%. Synthesis of 4 and formal total

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

Synthesis of 2-substituted tryptophans via a C3- to C2-alkyl migration

• Michele Mari,
• Simone Lucarini,
• Francesca Bartoccini,
• Giovanni Piersanti and
• Gilberto Spadoni

Beilstein J. Org. Chem. 2014, 10, 1991–1998, doi:10.3762/bjoc.10.207

• such as trifluoroethanol (TFE) did not accelerate the reaction and still gave low yields after 24 h (Table 1, entry 5). Next, we tested the effect of different acids on the reaction. Although some Lewis acids such as TiCl4, SnCl4, and Sc(OTf)3 did not show beneficial effects (Table 1, entries 6–8), a

Structure/affinity studies in the bicyclo-DNA series: Synthesis and properties of oligonucleotides containing bc^en-T and iso-tricyclo-T nucleosides

• Branislav Dugovic,
• Michael Wagner and
• Christian J. Leumann

Beilstein J. Org. Chem. 2014, 10, 1840–1847, doi:10.3762/bjoc.10.194

• , quant.; (e) TBAF, THF, rt, 19 h, 95%; (f) thymine, BSA, SnCl4, CH3CN, 0 °C → rt, 17 h, 56% 7β + 22% (7α/β 2.5:1); (g) Bu4NOH, H2O/dioxane, rt, 16 h, 94%; (h) DMTrCl, pyridine, CH2Cl2, rt, 24 h, 98%; (i) CEP-Cl, DIPEA, THF, rt, 4 h, 89%. Conditions: (a) thymine, BSA, TMSOTf, TMSCl, CH3CN, rt, 2.5 h; (b

Synthesis of rigid p-terphenyl-linked carbohydrate mimetics

• Maja Kandziora and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 1749–1758, doi:10.3762/bjoc.10.182

• and protection of 12a to 1,2-oxazine derivative 13. Conditions: a) 1. SnCl4, CH3CN, 4 h, −30 °C → rt; 2. TBSCl, imidazole, THF, 4 h, rt; b) NaBH4, EtOH, 4 h, −40 °C, 72%, dr 81:19; c) L-selectride, THF, 2 h, −10 °C, 73%, only 12a; d) TBSOTf, 2,6-lutidine, THF, 2 h, 0 °C. Synthesis of bicyclic diols 15

• and of trityl-protected bicyclic 1,2-oxazine 16. Conditions: a) SnCl4, CH3CN, 18 h, −30 °C → rt, b) 1) L-selectride, THF, 4 h, −15 °C, dr 72:28; 2) separation by column chromatography (silica gel, hexanes/EtOAc 1:1 → 1:2); c) TrtCl, DMAP, pyridine, 3 d, rt. Hydrogenolyses of bicyclic 1,2-oxazine

Concise total synthesis of two marine natural nucleosides: trachycladines A and B

• Haixin Ding,
• Wei Li,
• Zhizhong Ruan,
• Ruchun Yang,
• Zhijie Mao,
• Qiang Xiao and
• Jun Wu

Beilstein J. Org. Chem. 2014, 10, 1681–1685, doi:10.3762/bjoc.10.176

• .10.176 Abstract We report the first total synthesis of trachycladines A (10 steps, 34.2% overall yield) and B (11 steps, 35.0% overall yield) by using 5-deoxy-1,2,3-tri-O-acetyl-β-D-ribofuranose as the starting material. The critical step was the SnCl4 assisted regio- and steroselective deprotection of

• available with a cheap market price. In addition, the regioselective cleavage of the 2-O-benzyl protection group of perbenzylated 1-O-methyl ribofuranoside by using SnCl4 has been widely used for the synthesis of 2-O-substituted nucleosides [26][27][28][29][30]. To the best of our knowledge, an application

• it is less irritant than the usually used benzyl bromide. Regioselective cleavage of the 2-O-(2,4-dichlorobenzyl) group was attempted with anhydrous SnCl4 in DCM by the method reported by Brown [31][32] and our group [16]. To our delight, this approach can afford 3-O-(2,4-dichlorobenzyl)-1-O-methyl-α

Clicked and long spaced galactosyl- and lactosylcalix[4]arenes: new multivalent galectin-3 ligands

• Silvia Bernardi,
• Paola Fezzardi,
• Gabriele Rispoli,
• Stefania E. Sestito,
• Francesco Peri,
• Francesco Sansone and
• Alessandro Casnati

Beilstein J. Org. Chem. 2014, 10, 1672–1680, doi:10.3762/bjoc.10.175

• ), which is very difficult to separate by flash chromatographic methods. On the other hand, the recently reported glycosylation reactions of lactose peracetate exploiting SnCl4 and CF3CO2Ag as promoters [46] gave compound 14 mainly as a β-anomer (α/β ratio 1:4) in 74% isolated yield. The subsequent

Expedient synthesis of 1,6-anhydro-α-D-galactofuranose, a useful intermediate for glycobiological tools

• Luciana Baldoni and
• Carla Marino

Beilstein J. Org. Chem. 2014, 10, 1651–1656, doi:10.3762/bjoc.10.172

• from galactose (Scheme 1) [16]. The 1,6-ring closure was produced by the O-debenzylation of the 6-hydroxy group of 4 and the nucleophilic attack of this hydroxy group to C-1, promoted by SnCl4. An optimized synthesis of 2 following this strategy has recently been described with an overall yield of 48

• ’ of 12 [32]. In between these two signals an intense doublet corresponding to equivalent H-6,6´ (3.58 ppm) of 11 was observed, in accordance with the behavior of other free HO-galactofuranosides [38], which supports the intermediate formation of 11. The treatment of 9 with SnCl4 afforded compound 12

cis–trans Isomerization of silybins A and B

• Michaela Novotná,
• Radek Gažák,
• David Biedermann,
• Florent Di Meo,
• Petr Marhol,
• Marek Kuzma,
• Lucie Bednárová,
• Kateřina Fuksová,
• Patrick Trouillas and
• Vladimír Křen

Beilstein J. Org. Chem. 2014, 10, 1047–1063, doi:10.3762/bjoc.10.105

• to be the most suitable Lewis acid for silybin isomerization (Table 1). Other Lewis acids either gave lower isomerization yields (SnCl4), did not work at all, or even caused decomposition. Toluene-4-sulfonic acid, as a representative protic acid, gave no reaction under the same conditions. In this

An oxidative amidation and heterocyclization approach for the synthesis of β-carbolines and dihydroeudistomin Y

• Suresh Babu Meruva,
• Akula Raghunadh,
• Raghavendra Rao Kamaraju,
• U. K. Syam Kumar and
• P. K. Dubey

Beilstein J. Org. Chem. 2014, 10, 471–480, doi:10.3762/bjoc.10.45

• with different Lewis acids such as BF3·Et2O, SnCl4, TiCl4 etc., in mutiple solvents under various reaction conditions. The best conversion was obtained when the reaction was conducted in BF3·Et2O in ether at 25–30 °C and the product dihydro-β-carboline 7 was isolated in 55% of yield. The formation of

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

• -trioxolanes can be trapped with allyltrimethylsilane. For example, the SnCl4-mediated fragmentation of ozonides 84a–l in the presence of allyltrimethylsilane in dichloromethane gives a complex mixture of products 85–94, including dioxolanes 86a–i, 87i, 90j–l, and 91j (Scheme 25, Table 8) [256]. Treatment of

• the bicyclic ozonide 1-methyl-6,7,8-trioxabicyclo[3.2.1]octane 84m, with SnCl4 in the presence of allyltrimethylsilane produces a mixture of two cis diastereomers and two trans diastereomers (in a ratio of 35:35:15:15) of 7-(3-methyl-5-((trimethylsilyl)methyl)-1,2-dioxolan-3-yl)hept-1-en-4-ol 95 in a

• acetate-catalyzed synthesis of cyclic peroxides [336]. 3.10. Acid-mediated cyclizations of peroxides The intramolecular cyclization of unsaturated peroxyacetals 273a–d in the presence of TiCl4 or SnCl4 occurs via formation of peroxycarbenium ions to give methoxy- and chlorine-containing dioxanes 274a–d as

Sequential Diels–Alder/[3,3]-sigmatropic rearrangement reactions of β-nitrostyrene with 3-methyl-1,3-pentadiene

• Peter A. Wade,
• Alma Pipic,
• Matthias Zeller and
• Panagiota Tsetsakos

Beilstein J. Org. Chem. 2013, 9, 2137–2146, doi:10.3762/bjoc.9.251

• solution of 3-methyl-1,3-pentadiene (either 1a or 1b, 2 mmol) in CH2Cl2 (2 mL) was added dropwise (syringe pump) over 1 h to a cold (−78 °C) mixture of SnCl4 (0.5 equiv), β-nitrostyrene (0.5 equiv), and CH2Cl2 (10 mL). The resulting cold solution was stirred for 40 min. Dichloromethane (10 mL) and then

Total synthesis of (−)-epimyrtine by a gold-catalyzed hydroamination approach

• Thi Thanh Huyen Trinh,
• Khanh Hung Nguyen,
• Patricia de Aguiar Amaral and
• Nicolas Gouault

Beilstein J. Org. Chem. 2013, 9, 2042–2047, doi:10.3762/bjoc.9.242

• stereospecifically the corresponding piperidone 4 in 80% yield. Subsequent bromination with CBr4 in the presence of PPh3 (Appel reaction) gave 5 in 84% yield. Finally, deprotection with 1 M SnCl4 in dichloromethane then neutralization by using K2CO3 afforded the final product (−)-epimyritine in a 80% yield. N-Cbz

• , 370.0990. To a solution of 5 (263 mg, 0.75 mmol, 1 equiv) in 5 mL of CH2Cl2 under argon atmosphere was added a solution of 1 M SnCl4 in CH2Cl2 (3.8 mL, 5.0 equiv). The reaction was stirred at room temperature for 3 h. The solvent was removed under reduced pressure. Then 25 mL of THF and 40 mL of an

Diastereoselective synthesis of nitroso acetals from (S,E)-γ-aminated nitroalkenes via multicomponent [4 + 2]/[3 + 2] cycloadditions promoted by LiCl or LiClO₄

• Leandro Lara de Carvalho,
• Robert Alan Burrow and
• Vera Lúcia Patrocinio Pereira

Beilstein J. Org. Chem. 2013, 9, 838–845, doi:10.3762/bjoc.9.96

• addition of a Lewis acid as a promoter reaction; however, a limited number of these species have been employed in these reactions, e.g., SnCl4 or Ti(O-iPr)2Cl2 [1][2][3]. However, LiClO4 or LiCl solutions have not been used in tandem nitroalkene cycloadditions, although they are widely employed as

Iron-containing mesoporous aluminosilicate catalyzed direct alkenylation of phenols: Facile synthesis of 1,1-diarylalkenes

• Satyajit Haldar and
• Subratanath Koner

Beilstein J. Org. Chem. 2013, 9, 49–55, doi:10.3762/bjoc.9.6

• reagents to afford 1,1-disubstituted olefins [27]. Alternatively, Friedel–Crafts-type alkenylation could be a better choice to prepare such regiospecific vinyl aromatic compounds. Yamaguchi et al. reported a direct ortho alkenylation of phenols with 1-alkynes using SnCl4 and Bu3N in acetonitrile under

Facile isomerization of silyl enol ethers catalyzed by triflic imide and its application to one-pot isomerization–(2 + 2) cycloaddition

• Kazato Inanaga,
• Yu Ogawa,
• Yuuki Nagamoto,
• Akihiro Daigaku,
• Hidetoshi Tokuyama,
• Yoshiji Takemoto and
• Kiyosei Takasu

Beilstein J. Org. Chem. 2012, 8, 658–661, doi:10.3762/bjoc.8.73

• triethylammonium chloride promotes the isomerization to give thermodynamically favourable ones in moderate yield [5]. However, harsh conditions (reaction temperature: ca. 100 to 200 °C) were required for the complete equilibration. Yamamoto and co-workers reported that a SnCl4–(BINOL monomethyl ether) complex (5

A concise synthesis of 3-(1-alkenyl)isoindolin-1-ones and 5-(1-alkenyl)pyrrol-2-ones by the intermolecular coupling reactions of N-acyliminium ions with unactivated olefins

• Nianhong Lu,
• Lihong Wang,
• Zhanshan Li and
• Wei Zhang

Beilstein J. Org. Chem. 2012, 8, 192–200, doi:10.3762/bjoc.8.21

• 1-alkenylboronic acid, or esters [23][24] besides allylsilane. For example, Angst reported the coupling of styrylsilanes with N-acyl-2-chloroglycine esters catalyzed by SnCl4 to give the 3-styryl glycine derivatives in 1987 [19]; Wistrand reported the coupling of methyl 1-acyl-5-methoxy-L-proline

• was very efficient for the formation of 3a compared to other catalysts such as CF3SO3H, CH3CO2H, TiCl4, SnCl4 and InCl3. Among various solvents tested, anhydrous dichloromethane (DCM) appeared to be the best choice, providing the desired adduct in the highest yield (>80%). Thus, the reaction employing

Development of the titanium–TADDOLate-catalyzed asymmetric fluorination of β-ketoesters

• Lukas Hintermann,
• Mauro Perseghini and
• Antonio Togni

Beilstein J. Org. Chem. 2011, 7, 1421–1435, doi:10.3762/bjoc.7.166

• significant catalytic activity was observed in this specific model reaction (Scheme 3). The fluorination of cyanoester 3 with F–TEDA was not accelerated by any of the potential catalysts investigated (TiCl4, BF3·Et2O, SnCl4, Sn(OTf)2, AlCl3, Mg(OTf)2, ZnF2 or SbF3). The conversion 3→3-F in a blank reaction

Synthesis, reactivity and biological activity of 5-alkoxymethyluracil analogues

• Lucie Brulikova and
• Jan Hlavac

Beilstein J. Org. Chem. 2011, 7, 678–698, doi:10.3762/bjoc.7.80

• protected by the silylation with hexamethyldisilazane. Subsequently, this modified uracil was reacted with protected 2-deoxyribose in the presence of SnCl4. Finally, protected α- and β-anomers 111 and 109 were treated with methanolic sodium methoxide to afford the nucleosides 112 and 110. Synthesis of

Stereoselective synthesis of four possible isomers of streptopyrrolidine

• Debendra K. Mohapatra,
• Barla Thirupathi,
• Pragna P. Das and
• Jhillu S. Yadav

Beilstein J. Org. Chem. 2011, 7, 34–39, doi:10.3762/bjoc.7.6

• investigated (SnCl4, BF3·OEt2, ZnI2, TiCl4, EtOAc/LDA/ZnBr2) BF3·OEt2 gave excellent selectivity (exclusively 8b) (Table 1). Following a modification of the Mosher method [32][33], the newly created stereogenic center in compound 8b bearing the hydroxyl group was assigned. The syntheses of both the (S)- and (R

• , 0.8 mmol) in CH2Cl2 (5 mL) under a nitrogen atmosphere and cooled to −78 °C, was added 1 M solution of SnCl4 in CH2Cl2 (0.1 mL, 0.81 mmol). After 10 min, (1-ethoxyvinyloxy)trimethylsilane (0.26 g, 1.6 mmol) was added at the same temperature. The reaction mixture was stirred for 1 h at −78 °C. After

• ) SnCl4, (1-ethoxyvinyloxy)trimethylsilane, CH2Cl2, −78 °C, 2 h, 70% (8a:8b = 3:7); (d) LDA, EtOAc, ZnBr2, −78 °C, 1 h, 82%, (8a:8b = 95:5). Reagents and conditions: (a) (1) TFA, CH2Cl2, rt, 4 h; (2) Zr(OtBu)4, HOAt, toluene, 60 °C, 12 h, 82% over two steps. Addition reaction under different conditions to

Aromatic and heterocyclic perfluoroalkyl sulfides. Methods of preparation

• Vladimir N. Boiko

Beilstein J. Org. Chem. 2010, 6, 880–921, doi:10.3762/bjoc.6.88

• -isomers [87]. Unlike pyrroles, furan, thiophene and selenophene react with CF3SCl only in the presence of catalysts. For selenophene [84] and thiophenes [85] SnCl4 is sufficient, whilst furans require more forcing conditions usually involving prolonged heating (20 h at 60 °C) and in pyridine for