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

• trifluoromethanesulfonate (TMSOTf) and 1.5 equiv triethylamine (Et3N) in dichloromethane for 4 hours. Then the mixture was cooled down to 0 °C and 1 equiv of p-nitrobenzaldehyde and 0.3 equiv of TiCl4 were added under stirring. Stirring at room temperature was continued for 15 hours. Then the reaction was quenched by the

• yield, while the syn/anti-ratio was not changed (Table 1, entry 2). Elongation of the reaction time resulted in the formation of more side products, drop of aldol products’ yield and selectivity (Table 1, entry 3). A lower amount of TMSOTf (1.2 equiv) led to increased yield but lower selectivity (Table

• with benzaldehyde, p-nitro-, and p-methoxybenzaldehyde as described recently by Ponomarenko and Röschenthaler et al. [34]. Considering our earlier results [31] on TMSOTf-mediated Claisen-type rearrangements of SF5-acetates of allyl alcohols, we favor the initial formation of (Z)-enolates (ketene

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

Beilstein J. Org. Chem. 2018, 14, 25–53, doi:10.3762/bjoc.14.3

• reductive opening of benzylidene acetal using the borane−THF complex in the presence of Bu2BOTf. Regioselective TMSOTf-catalysed glycosylation of the diol 4 by the imidate donor 3 resulted in the formation of a single product, the β(1→6)-linked disaccharide 5. After the 2’-N-Fmoc group in 5 was removed with

• reductive opening of the benzylidene acetal to give the acceptor monosaccharide 63. NIS/TMSOTf-promoted glycosylation of 63 with glycosyl donor 64 furnished desired β(1→6) disaccharide which was subjected to treatment with hydrazine hydrate to remove the phthalimido group. Subsequent acylation of the

Ring-size-selective construction of fluorine-containing carbocycles via intramolecular iodoarylation of 1,1-difluoro-1-alkenes

• Takeshi Fujita,
• Ryo Kinoshita,
• Tsuyoshi Takanohashi,
• Naoto Suzuki and
• Junji Ichikawa

Beilstein J. Org. Chem. 2017, 13, 2682–2689, doi:10.3762/bjoc.13.266

• -difluoroallyl)biphenyl (1a) as a model substrate. To generate a highly reactive, cationic iodine species, several iodine sources were used with acid or metal activators (Table 1, entries 1–3). Upon treatment with N-iodosuccinimide (NIS) and trimethylsilyl trifluoromethanesulfonate (TMSOTf) in a 1:1 mixed

• fluorine substituents in the three-membered iodonium intermediates. Since the combination of NIS and TMSOTf was found to be the best for an iodoarylation of 5, the reactions of a couple of 2-(3,3-difluoroallyl)biaryls 5 were examined under the same conditions (Scheme 4). The iodoarylation of

An efficient synthesis of 1,6-anhydro-N-acetylmuramic acid from N-acetylglucosamine

• Matthew B. Calvert,
• Christoph Mayer and
• Alexander Titz

Beilstein J. Org. Chem. 2017, 13, 2631–2636, doi:10.3762/bjoc.13.261

• -anhydroGlcNAc was carried out according to Tyrtysh et al. [12]. A suspension of 4 (203 mg, 1.0 mmol) in dichloromethane (10 mL) was treated with collidine (264 µL, 2.0 mmol) at room temperature. Trityl triflate (0.3 M in dichloromethane, 5 mL, generated freshly by mixing equimolar quantities of TMSOTf and TrOH

Phosphonic acid: preparation and applications

• Charlotte M. Sevrain,
• Mathieu Berchel,
• Hélène Couthon and
• Paul-Alain Jaffrès

Beilstein J. Org. Chem. 2017, 13, 2186–2213, doi:10.3762/bjoc.13.219

• nucleophilic halide anion is another feature of this reaction. Indeed the treatment of TMSOTf on a phosphonate did not induce the dealkylation likely due to the absence of nucleophilic species [161]. It is worth noticing that the nucleophilic attack of bromide only occurs on alkyl chains as exemplified by a

Preactivation-based chemoselective glycosylations: A powerful strategy for oligosaccharide assembly

• Weizhun Yang,
• Bo Yang,
• Sherif Ramadan and
• Xuefei Huang

Beilstein J. Org. Chem. 2017, 13, 2094–2114, doi:10.3762/bjoc.13.207

• of PhSeBr. PhSeBr could react with the remaining donor 4 for quantitative activation of 4. The addition of the acceptor to the reaction mixture upon donor preactivation afforded orthoester 6. The orthoester 6 was rearranged in situ with trimethylsilyl trifluoromethanesulfonate (TMSOTf) to

• disaccharide 7, which could be subjected to bromine-promoted glycosylation for further chain elongation. As an example, preactivation of a monosaccharide 8 with bromine was followed by the addition of a bifunctional disaccharide building block 10 and subsequent TMSOTf-promoted orthoester rearrangement

• /AgOTf [18], N-iodosuccinimide (NIS)/TMSOTf [18], dimethyl(methylthio)sulfonium triflate (DMTST) [18], 1-(benzenesulfinyl)piperidine (BSP)/Tf2O [18][19][49], S-(4-methoxyphenyl)benzene-thiosulfinate (MBPT)/Tf2O [50], Ph2SO/Tf2O [36][51], O,O-dimethylthiophosphonosulfenyl bromide (DMTPSB)/AgOTf [52], and

Intramolecular glycosylation

• Xiao G. Jia and
• Alexei V. Demchenko

Beilstein J. Org. Chem. 2017, 13, 2028–2048, doi:10.3762/bjoc.13.201

• intramolecular glycosylation, probably due to steric interactions. A glycine residue spacer was found necessary to separate the two rigid Hyp bound counterparts. Thus, glycosylation of conjugate 38 in the presence of NIS and TMSOTf resulted in the formation of the (1→4)-linked disaccharide 40 in 80% yield with

• obtained (Scheme 12). Following the NIS/TMSOTf-promoted glycosylation, macrocycle 50 was formed in 55% yield with exclusive α-stereoselectivity. Interestingly, when a similar template was attached to the O-2 position followed by glycosylation with the 3-hydroxy group, the reaction proceeded with high β

1,3-Dibromo-5,5-dimethylhydantoin as promoter for glycosylations using thioglycosides

• Fei-Fei Xu,
• Claney L. Pereira and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2017, 13, 1994–1998, doi:10.3762/bjoc.13.195

• trimethylsilyl trifluoromethanesulfonate (TMSOTf) were employed as co-promoters in solution or automated glycan assembly on solid phase. Keywords: automated glycan assembly; 1,3-dibromo-5,5-dimethylhydantoin; glycosylation; promoter; thioglycosides; Introduction Thioglycosides are versatile glycosylating

• modest yield (43%). When TfOH or TMSOTf (10 mol %) were added as co-promoter, the yield increased to more than 90% (Table 1, entries 2 and 3). Next, the amount of the reagent required for activation was studied (Table 1, entries 3–5). Substoichiometric amounts of DBDMH (0.7 equiv) in the presence of co

• oligosaccharides [20][47]. Ideally, stable and non-toxic reagents should be used on such instruments. The automated synthesis of disaccharide 16 served to assess the suitability of the DBDMH/TMSOTf activation system using functionalized resin 15 [48] as solid support (Scheme 1). After two coupling cycles with

Strategies toward protecting group-free glycosylation through selective activation of the anomeric center

• A. Michael Downey and
• Michal Hocek

Beilstein J. Org. Chem. 2017, 13, 1239–1279, doi:10.3762/bjoc.13.123

• anomeric center Davis and colleagues [51] developed a unique glycosylation strategy that employs a 4-bromobutanyl group as a self-activating aglycone on a mannose monomer (Scheme 13) which works even in the absence of any activating agent, such as TMSOTf. The synthesis of the self-activating donor proceeds

• very common and well-studied. Typical Lewis acids employed for anomeric activation are TMSOTf and BF3·Et2O (Scheme 14). The reactions proceed through an oxocarbenium ion that was very recently observed by NMR under cryogenic (−40 °C) conditions stabilized by the HF/SbF5 superacid [52]. The highly

• glycosides: A potentially attractive strategy for a 1,2-cis glycosylation has been described by Baker and colleagues [56] and employs the use of a deprotected thiol glycoside in the presence of a large excess of Lewis acid (TMSOTf) and N-iodosuccinimide (NIS). Although the stereoselectivity of the reaction

First total synthesis of kipukasin A

• Chuang Li,
• Haixin Ding,
• Zhizhong Ruan,
• Yirong Zhou and
• Qiang Xiao

Beilstein J. Org. Chem. 2017, 13, 855–862, doi:10.3762/bjoc.13.86

• , 2.2 mmol) in dry MeCN (15 mL) was added BSA (1.36 g, 6.7 mmol). The mixture was heated at 50 °C for 20 min. After cooled to room temperature, a solution of 16 (1.00 g, 1.7 mmol) in dry MeCN (5 mL) along with TMSOTf (1.30 g, 5.9 mmol) were added to the above reaction mixture at 0 °C. The solution was

• conditions: (a) I2, acetone, 0 °C to rt, 88%; (b) K2CO3, MeOH, rt, 93%; (c) 2-iodobenzoyl chloride, pyridine, −10 °C to rt, CH2Cl2, 80%; (d) 1-hexyne, PdCl2(PPh3)3, CuI, Et3N, THF, 50 °C , 78%; (e) 9, DMAP, Et3N, CH2Cl2, 0 °C to rt, 74%; (f) Ac2O, H2SO4, acetic acid, rt, 74%; (g) uracil, BSA, TMSOTf, MeCN

Total synthesis of a Streptococcus pneumoniae serotype 12F CPS repeating unit hexasaccharide

• Peter H. Seeberger,
• Claney L. Pereira and
• Subramanian Govindan

Beilstein J. Org. Chem. 2017, 13, 164–173, doi:10.3762/bjoc.13.19

• + 3] approach (Scheme 1, route A) to the synthesis of the repeating unit hexasaccharide 36 (Scheme 7) was attempted. The union of trisaccharides 2 and 3 using TMSOTf in acetonitrile as the activator did not yield the desired hexasaccharide 36. Instead, trisaccharide acceptor 3 missing its C6 silyl

• 44. Considering a potential “mismatch” [38] between the thioglycoside glycosylating agent and the acceptor [39][40] we explored whether the glucosyl trichloroacetimidate donor 6 (Scheme 1) would be more suitable. Indeed, glycosylation of disaccharide 42 with building block 6 using TMSOTf as the

• basic conditions using methyl iodide in 32% yield over three steps [41]. Next, TMSOTf activation of fucosyl trichloroacetimidate 8 (Scheme 1) catalyzed the glycosylation of methyl uronate 48 to afford pentasaccharide 49 exclusively as the α-isomer by virtue of remote participation of the 3-O-acetate

Silyl-protective groups influencing the reactivity and selectivity in glycosylations

• Mikael Bols and
• Christian Marcus Pedersen

Beilstein J. Org. Chem. 2017, 13, 93–105, doi:10.3762/bjoc.13.12

• protective groups on the donor a TES-protected trichloroacetimidate of fucose, 4, was employed by Myers et al. [7] in order to have protective groups compatible with their synthesis of neocarzinostatin. It was found that optimal glycosylation was performed with TMSOTf as a catalyst at low temperature and

Synthesis of the C8’-epimeric thymine pyranosyl amino acid core of amipurimycin

• Pramod R. Markad,
• Navanath Kumbhar and
• Dilip D. Dhavale

Beilstein J. Org. Chem. 2016, 12, 1765–1771, doi:10.3762/bjoc.12.165

• (1.5:1) in good yield (Scheme 6). Glycosylation of 21 with bis-silylated 2-(N-acetylamino)-6-chloropurine under a variety of reaction conditions was found to be unsuccessful. However, glycosylation of 21 with bis(trimethylsilyl)thymine in the presence of TMSOTf in dichloromethane led to the

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

Automated glycan assembly of a S. pneumoniae serotype 3 CPS antigen

• Markus W. Weishaupt,
• Stefan Matthies,
• Mattan Hurevich,
• Claney L. Pereira,
• Heung Sik Hahm and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2016, 12, 1440–1446, doi:10.3762/bjoc.12.139

• ensure complete glycosylation of the nucleophile (Scheme 1). The glycosyl phosphate building blocks 1 and 2 were activated by stoichiometric amounts of TMSOTf (trimethylsilyl trifluoromethanesulfonate) at −30 °C and reacted at this temperature for 30 min. Then the temperature was raised to −15 °C and

• deletion sequences (7 and 8) were also detected. Glycosylations mediated by the strongly acidic activator TMSOTf were found to be neutral when exiting the reaction vessel. An incomplete removal of the strongly basic deprotection solutions would result in quenching of the next glycosylations. Indeed, test

• ), 254 nm. Attempted assembly of SP3 trisaccharide 5 using glycosyl phosphate building blocks 1 and 2. Reagents and conditions: a) 2 (3 equiv), TMSOTf, CH2Cl2, −30 °C (30 min) to −15 °C (30 min), n = 3; b) Et3N in DMF (10% v/v), 25 °C (15 min), n = 3; c) 1 (3 equiv), TMSOTf, CH2Cl2, −30 °C (30 min) to

Synthesis of highly functionalized 2,2'-bipyridines by cyclocondensation of β-ketoenamides – scope and limitations

• Paul Hommes and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2016, 12, 1170–1177, doi:10.3762/bjoc.12.112

• corresponding β-ketoenamines 2a–e were converted into different β-ketoenamides 3a–g by N-acylation with 2-pyridinecarboxylic acid derivatives. These β-ketoenamides were treated with a mixture of TMSOTf and Hünig’s base to promote the cyclocondensation to 4-hydroxypyridine derivatives. Their immediate O

• compounds that are not accessible by alternative methods. Synthesis of highly functionalized 2,2'-bipyridines 4a and 5b from symmetrical 1,3-diketones 1a and 1b; TMSOTf = trimethylsilyl trifluoromethanesulfonate; DIPEA = N,N-diisopropylethylamine; NfF = nonafluorobutanesulfonyl fluoride. Synthesis of β

• the corresponding N-oxide 8. Suzuki-couplings of 2,2'-bipyrid-4-yl nonaflates 5a and 5b to compounds 9 and 10. Palladium-catalyzed couplings of chloro-substituted 2,2'-bipyrid-4-yl nonaflate 5g leading to compounds 11, 12 and 13. Attempted TMSOTf/DIPEA-promoted cyclocondensations of β-ketoenamides 3a

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

• by the electron-withdrawing acetoxy group. On the contrary, the TMSOTf-promoted glycosylation [39] (method E) of coniferyl alcohol 12 with trichloroacetimidate 14 at low temperature was found to be more efficient and glycoside 23 was obtained in high yield with full β-selectivity as proved by NMR

Synthesis of D-fructose-derived spirocyclic 2-substituted-2-oxazoline ribosides

• Madhuri Vangala and
• Ganesh P. Shinde

Beilstein J. Org. Chem. 2015, 11, 2289–2296, doi:10.3762/bjoc.11.249

• Madhuri Vangala Ganesh P. Shinde Department of Chemistry, Indian Institute of Science Education and Research, Pune 411 008, India 10.3762/bjoc.11.249 Abstract The TMSOTf-mediated synthesis of β-configured spirocyclic 2-substituted-2-oxazoline ribosides was achieved using a “Ritter-like” reaction

• acetonitrile was shown, illustrating the instability of spirooxazolines in comparison with fused oxazolines [37]. In our work, the activation of the β-D-psicofuranose derivative 5a with TMSOTf in acetonitrile exclusively resulted in the formation of spirooxazoline 6a. The stability of this compound inspired us

• compounds 3a and 5a were utilized to check the substrate feasibility in the formation of spirooxazolines. In our first experiment, compound 5a was reacted with acetonitrile as a nucleophilic participating solvent using TMSOTf at 0 °C, then the reaction was left at room temperature for 1 h. To our delight

Synthesis, antimicrobial and cytotoxicity evaluation of new cholesterol congeners

• Mohamed Ramadan El Sayed Aly,
• Hosam Ali Saad and
• Shams Hashim Abdel-Hafez

Beilstein J. Org. Chem. 2015, 11, 1922–1932, doi:10.3762/bjoc.11.208

• ] was coupled with cholest-5-en-3β-ol (1) as glycosyl acceptor in the presence of catalytic TMSOTf as promoter to afford 15 in 74% yield. The large anomeric coupling constant (J1,2 = 8.4 Hz) of the pyranoside moiety at δ = 5.30 ppm ensured the β-configuration of this glycoside. Deacetylation of

• , 100 °C (9b, 47%); (b) CuSO4·5H2O, L-AsAc, THF/H2O [11a, n = 4 (90%); 11b, n = 9 (67%)]; (c) CBr4, PPh3, DCM (59%). Reagents and conditions: CuSO4·5H2O, L-AsAc, THF/H2O (96%). Reagents and conditions: (a) 1, TMSOTF, CH3CN, rt (74%); (b) NaOMe, MeOH (84%); (c) NaOH; HCl (pH 5); Ac2O/Pyr; NaOMe/MeOH (37

• %); (d) 9a, TMSOTf, DCM (71%); (e) 10, CuSO4·5H2O, L-AsAc, THF/H2O (67%); (f) NaOMe, MeOH (75%). Reagents and conditions: (a) 9a, TMSOTF, DCM, rt (19%); (b) 10, CuSO4·5H2O, L-AsAc, THF/H2O (62%); (c) NaOMe/MeOH (78%). A: Ring A of the maltose moiety, B: Ring B of the maltose moiety. Reagents & conditions

Towards inhibitors of glycosyltransferases: A novel approach to the synthesis of 3-acetamido-3-deoxy-D-psicofuranose derivatives

• Maroš Bella,
• Miroslav Koóš and
• Chun-Hung Lin

Beilstein J. Org. Chem. 2015, 11, 1547–1552, doi:10.3762/bjoc.11.170

• in traces as a mixture with the corresponding α-anomer 16 (Scheme 3). Further attempts to achieve the thioglycosylation of D-psicofuranose derivative 11 under various conditions, including EtSH/TMSOTf/CH2Cl2, EtSH/TMSOTf and EtSH/CSA/CH2Cl2 did not improve the yield of the required 2-thio-β-D

Automated solid-phase synthesis of oligosaccharides containing sialic acids

• Chian-Hui Lai,
• Heung Sik Hahm,
• Chien-Fu Liang and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2015, 11, 617–621, doi:10.3762/bjoc.11.69

• cycles were initiated following programmed maneuvers. Each cycle starts with a TMSOTf acidic wash at −20 °C to ensure that no base from previous deprotection reactions remains and quenches the subsequent coupling. This problem had been observed earlier (data not shown) and can be overcome by this extra

• washing step. In addition, TMSOTf eliminates any moisture that may have resided on the resin or in the reaction vessel. Glycosylations were carried out using the optimized temperatures for each building block using twice five equivalents of building block and activator. Removal of the Fmoc protecting

• linkages. Glycosylations: a) 2 × 5 equiv TMSOTf, ACN/DCM (1:1), −50 °C (5 min), −30 °C (10 min), −20 °C (80 min), −10 °C (10 min), 0 °C (10 min) for 4 and 5. b) 2 × 5 equiv TfOH, NIS, DCM, −40 °C (5 min), −20 °C (30 min) for 6 and 7. c) 2 × 5 equiv TMSOTf, DCM/dioxane (3:2), 20 °C (90 min), for 8. d) 2 × 5

Synthesis of a hexasaccharide partial sequence of hyaluronan for click chemistry and more

• Marina Bantzi,
• Stephan Rigol and
• Athanassios Giannis

Beilstein J. Org. Chem. 2015, 11, 604–607, doi:10.3762/bjoc.11.67

• ][23] was linked with glycosyl acceptor 2 [24][25] using TMSOTf as promoter to obtain disaccharide 4 in 90% yield. Likewise, reaction of glycosyl donor 1 with monosaccharide 3 [26] and subsequent O-TBS group cleavage with Olah's reagent [27], afforded disaccharide 5 in 86% yield. Thence, both

Articulated rods – a novel class of molecular rods based on oligospiroketals (OSK)

• Pablo Wessig,
• Roswitha Merkel and
• Peter Müller

Beilstein J. Org. Chem. 2015, 11, 74–84, doi:10.3762/bjoc.11.11

• –Martin-periodinane. iii: pentaerythritol, pTsOH (cat.). iv: 2-(4-methoxybenzyloxy)acetic acid, DCC, HOBt. v: (COCl)2/DMSO. vi: NaH, TMSCl, TMSOTf, vii DDQ, DCM, buffer pH 7). Synthesis of articulated rod 11 (i: CBr4, PPh3, NaN3. ii: K2CO3/MeOH. iii: Cu/C DCM/MeOH 1:1, cat. Et3N). Sequential deprotection

• of 11 and synthesis of triple articulated rod 14 (i: K2CO3/MeOH. ii: CBr4/PPh3/NaN3.iii: Cu/C, Et3N. iv: CBr4/PPh3/NaN3.). Synthesis of articulated rods 23–25 with increased solubility (i: 4-hydroxypiperidine, DCC, HOBt. ii: (COCl)2/DMSO. iii: 6, NaH, TMSCl, TMSOTf. iv: DDQ. v: K2CO3/MeOH. vi: CBr4

• /MeOH). Synthesis of articulated rods 32a–c (i: NaH, TMSCl, TMSOTf. ii: Cu/C, Et3N). Synthesis of articulated rods 33, 34 and 36. Synthesis of articulated rod 39 (i: cinnamoyl chloride, DMAP, pyridine. ii: DMF 120 °C). Synthesis of functionalized articulated rod 43 (i: PYBOP, Et3N. ii: KOH, H2O. iii

Synthesis of the pentasaccharide repeating unit of the O-antigen of E. coli O117:K98:H4

• Pintu Kumar Mandal

Beilstein J. Org. Chem. 2014, 10, 2724–2728, doi:10.3762/bjoc.10.287

• following the reaction pathway depicted in Scheme 2. Glycosylation of 3-azidopropyl 2,3,6-tri-O-benzyl-β-D-galactopyranoside (2) with the thioglycoside donor 3 in the presence of N-iodosuccinimide (NIS) and trimethylsilyl trifluoromethanesulfonate (TMSOTf) [26][27] gave disaccharide derivative 8 in 72

• . Reagents: (a) N-iodosuccinimide (NIS), TMSOTf, CH2Cl2, MS 4 Å, −30 °C, 1 h, 72%; (b) HClO4/SiO2, CH3CN, rt, 20 min, 85%; (c) benzoyl cyanide, DCM/pyridine, rt, 2 h, 80%; (d) N-iodosuccinimide (NIS), TfOH, CH2Cl2, MS 4 Å, −30 °C, 1 h, then 0 °C, 1 h, 77%; (e) NOBF4, Et2O/CH2Cl2 (3:1), −15 °C, 1 h, 75%; (f

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

• , India 10.3762/bjoc.10.277 Abstract A novel metal-free strategy for a rapid and α-selctive C-alkynylation of glycals was developed. The reaction utilizes TMSOTf as a promoter to generate in situ trimethylsilylacetylene for C-alkynylation. Thanks to this methodology, we can access C-glycosides in a

• single step from a variety of acetylenes , i.e., arylacetylenes and most importantly aliphatic alkynes. Keywords: α-selective; C-alkynylation; glycal; metal free; TMSOTf; Introduction C-Glycosides represent an important class of carbohydrate mimics, owing to their presence in a large number 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