Total synthesis of the O-antigen repeating unit of Providencia stuartii O49 serotype through linear and one-pot assemblies

• Tanmoy Halder and
• Somnath Yadav

Beilstein J. Org. Chem. 2021, 17, 2915–2921, doi:10.3762/bjoc.17.199

• described in Scheme 2. With the monosaccharide building blocks in hand, the galactosamine donor 6 was coupled with galactose acceptor 7 by activation of the thioglycoside using N-iodosuccinimide (NIS) in the presence of TMSOTf to afford the desired disaccharide β-ᴅ-GalpNHTroc-(1→4)-α-ᴅ-Galp (4) in 85% yield

• , as a single isomer (Scheme 3). Then, the chloroacetyl group was selectively removed using thiourea and 2,4,6-collidine [47] to afford the 3’-OH acceptor 5 in 87% yield. Finally, NIS/TMSOTf-promoted coupling of donor 3 with disaccharide acceptor 5 provided the desired β-linked trisaccharide 2 in 89

• acceptor 9 in the presence of TMSOTf as promoter (Scheme 5). After 1 h of reaction, TLC monitoring indicated the full consumption of the starting materials. Analysis of a small aliquot of the reaction mixture by HRMS confirmed the formation of the desired disaccharide. Then, to the same pot, the second

Synthetic strategies toward 1,3-oxathiolane nucleoside analogues

• Umesh P. Aher,
• Dhananjai Srivastava,
• Girij P. Singh and
• Jayashree B. S

Beilstein J. Org. Chem. 2021, 17, 2680–2715, doi:10.3762/bjoc.17.182

• isolated oxathiolane precursor 41, as discussed earlier, by enzymatic resolution of an acetoxy sulfide by a Pseudomonas fluorescens lipase. Using this pure precursor 41, the synthesis of 3TC (1) was accomplished by N-glycosylation with silylated base using trimethylsilyl trifluoromethanesulfonate (TMSOTf

• . [40] described coupling of crude 1,3-oxathiolane precursor 20 with silylated acetylcytosine utilizing TMSOTf as a Lewis acid, which gave a mixture of α- and β-anomers (1:2 ratio) of 81 (Scheme 30). The mixture of anomers was further separated by silica gel column chromatography. (+)-BCH-189 (1a) and

• synthetic procedure to access (−)-BCH-189 (1). Compound 20a was synthesized from ʟ-gulose derivative 3f (Scheme 6). The glycosylation reaction of oxathiolane intermediate 20a with silylated N4-acetylcytosine in dichloroethane using TMSOTf as a catalyst gave 81a as a β/α 2:1 mixture (Scheme 31). Separation

Synthesis of new bile acid-fused tetrazoles using the Schmidt reaction

• Dušan Đ. Škorić,
• Olivera R. Klisurić,
• Dimitar S. Jakimov,
• Marija N. Sakač and
• János J. Csanádi

Beilstein J. Org. Chem. 2021, 17, 2611–2620, doi:10.3762/bjoc.17.174

• trifluoromethanesulfonate (TMSOTf) is superior to BF3⋅OEt2 as a catalyst in both dichloromethane (DCM) and acetonitrile (ACN), while ACN appears to be the better choice as solvent. A particularly good yield was obtained with TMSOTf in ACN. Also, it is evident that an increase in the amount of TMSN3 and Lewis acid did not

• provide any significant change in yield. Myers and co-workers described BF2OTf⋅OEt2 as a powerful Lewis acid formed in situ from BF3⋅OEt2 and TMSOTf, which was especially efficient in ACN [45]. This prompted us to investigate the application of BF2OTf⋅OEt2 in our synthesis (Table 1, entries 9–11). As we

• expected, the reaction in ACN was the most efficient, while in DCM, there were no significant differences between BF2OTf⋅OEt2 and TMSOTf. Lowering reaction temperature in ACN (Table 1, entry 10) increased the yield of the tetrazole 13. Again, an increased amount of TMSN3 and catalyst did not provide any

Progress and challenges in the synthesis of sequence controlled polysaccharides

• Giulio Fittolani,
• Theodore Tyrikos-Ergas,
• Denisa Vargová,
• Manishkumar A. Chaube and
• Martina Delbianco

Beilstein J. Org. Chem. 2021, 17, 1981–2025, doi:10.3762/bjoc.17.129

• (1–3)-Xyl hexamer, an analogue of xylans found in algae cell-walls [206]. TMSOTf promoted the glycosylation of the Bz-protected disaccharide acceptor with the Bz-protected tetrasaccharide trichloroacetimidate donor. Although not yet reported, the authors suggested that this method can be extended to

N-tert-Butanesulfinyl imines in the asymmetric synthesis of nitrogen-containing heterocycles

• Joseane A. Mendes,
• Paulo R. R. Costa,
• Miguel Yus,
• Francisco Foubelo and
• Camilla D. Buarque

Beilstein J. Org. Chem. 2021, 17, 1096–1140, doi:10.3762/bjoc.17.86

• ), which has been shown to display memory-enhancing properties and was also effective for the treatment of cognitive disorders. The reaction of the N-tert-butanesulfinyl imine (SS)-119 with trimethylsilyl enol ether derived from acetophenone 123 in the presence of TMSOTf at low temperature, produced β

Synthetic accesses to biguanide compounds

• Oleksandr Grytsai,
• Cyril Ronco and
• Rachid Benhida

Beilstein J. Org. Chem. 2021, 17, 1001–1040, doi:10.3762/bjoc.17.82

• yields (1–72%) (Scheme 8B) [26]. Another variant using trimethylsilyl trifluoromethanesulfonate (TMSOTf) under classical heating conditions in 1,2-dichloroethane has been recently described by Kim et al. [27] to produce phenformin analogs with variable, but generally fairly good yields (4–100%) (Scheme 9

• alkylcyanoguanidines by TMSOTf was also tested by Kim et al. (Scheme 18) [27]. This method proved highly efficient to produce diversely substituted N1,N5-alkylbiguanides as phenformin derivatives, with yields generally excellent (≥94%). Interestingly, the addition of acetyl hydrazide was also tried and delivered the

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• Sakurai macrocyclization/dimerization strategy to produce 150 in the presence of TMSOTf, as shown in Scheme 35 [70]. Hoye and Hu utilized camphor sulfonic acid (CSA) to construct a cis-2,6-disubstituted tetrahydropyran 153 via an intramolecular Sakurai cyclization reaction between the enal 151 and an

• and trans-2,6-DHP, respectively, was reported by a [4 + 2]-annulation strategy. The authors utilized crotylsilanes syn-170 and anti-170, respectively, with an aldehyde 171 in the presence of TMSOTf to deliver different DHPs 172 (Scheme 41) [76]. For syn-170, the reaction went via the favored boat-like

• hydroxyallylsilane 186 with excellent enantioselectivity (Scheme 45) [83][84][85]. This, upon further reaction with another aldehyde in the presence of TMSOTf, gave 2,6-disubstituted 4-methylenetetrahydropyran 187. This strategy was utilized for the synthesis of bryostatin and (+)-dactyloide analogs [86][87][88

Access to highly substituted oxazoles by the reaction of α-azidochalcone with potassium thiocyanate

• Mysore Bhyrappa Harisha,
• Pandi Dhanalakshmi,
• Rajendran Suresh,
• Raju Ranjith Kumar and
• Shanmugam Muthusubramanian

Beilstein J. Org. Chem. 2020, 16, 2108–2118, doi:10.3762/bjoc.16.178

• have reported the TMSOTf-catalyzed synthesis of highly substituted imidazoles from α-azidochalcones under mild conditions [65]. As a sequel, the synthesis of oxazoles with an arylimino substituent has been accomplished in this work. The biologically important arylimino group [66][67][68][69] integrated

Synthesis of monophosphorylated lipid A precursors using 2-naphthylmethyl ether as a protecting group

• Jundi Xue,
• Ziyi Han,
• Gen Li,
• Khalisha A. Emmanuel,
• Cynthia L. McManus,
• Qiang Sui,
• Dongmian Ge,
• Qi Gao and
• Li Cai

Beilstein J. Org. Chem. 2020, 16, 1955–1962, doi:10.3762/bjoc.16.162

• ). The 3-hydroxy group in 5 was then protected as a Nap ether through a TMSOTf-catalyzed one-pot reductive naphthylmethylation process [17][18], by which free hydroxy groups were first trimethylsilylated in situ with hexamethyldisiloxane ((TMS)2O) before being naphthylmethylated by treatment with 2

• -naphthaldehyde, trimethylsilyl trifluoromethanesulfonate (TMSOTf), and triethylsilane (Et3SiH) [17][19]. On a 10 g scale, the protected methyl ester 6 could be purified by recrystallization followed by filtration to remove the major byproduct 2-methylnaphthalene. Subsequent saponification of the methyl ester 6

• -protected (R)-3-hydroxytetradecanoic acid (7). Conditions: (a) Meldrum's acid, pyridine, CH2Cl2, 0 °C; (b) CH3OH, reflux, 77% over two steps; (c) (R)-Ru(OAc)2(BINAP), H2, CH3OH, 65 °C, 98%; (d) NapCHO, TMSOTf, (TMS)2O, Et3SiH, THF, 0 °C; (e) LiOH, THF, H2O, 65 °C, 78% (over two steps). Synthesis of

Synthesis of 3-substituted isoxazolidin-4-ols using hydroboration–oxidation reactions of 4,5-unsubstituted 2,3-dihydroisoxazoles

• Lívia Dikošová,
• Júlia Laceková,
• Ondrej Záborský and
• Róbert Fischer

Beilstein J. Org. Chem. 2020, 16, 1313–1319, doi:10.3762/bjoc.16.112

• the C-3 carbon atom. The obtained products were benzoylated with benzoyl chloride/pyridine in the presence of DMAP to give the fully benzoylated isoxazolidine-4,5-diols 6a and 6b, which were subsequently treated with Et3SiH (3 equiv) and TMSOTf (2 equiv) in anhydrous CH2Cl2 at room temperature for 2 h

Copper-catalysed alkylation of heterocyclic acceptors with organometallic reagents

• Yafei Guo and
• Syuzanna R. Harutyunyan

Beilstein J. Org. Chem. 2020, 16, 1006–1021, doi:10.3762/bjoc.16.90

• research. In an attempt to overcome this reactivity issue, the same authors decided to use the trimethylsilyl-based Lewis acid TMSOTf in order to allow the covalent activation of the alkenylpyridine via pyridinium formation. This strategy turned out successful, and optimisation studies identified reaction

• conditions that allowed highly enantioselective ACAs of Grignard reagents to alkenylpyridines (Scheme 15) [46]. Using the optimised conditions (Cu/L7/TMSOTf), a large variety of pyridine-based chiral compounds was synthesized. Apart from allowing the introduction of different linear, branched, cyclic, and

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

• 8 only affording an unidentifiable mixture of compounds. Similarly, the 2,7-anhydro backbone of 11 was not cleaved under the above conditions and results in either recovered starting material or unidentifiable mixtures. Differently, ring-opening reactions of 6 with BF3⋅OEt2, TMSOTf, and Sc(OTf)3 in

Regioselectivity of glycosylation reactions of galactose acceptors: an experimental and theoretical study

• Enrique A. Del Vigo,
• Carlos A. Stortz and
• Carla Marino

Beilstein J. Org. Chem. 2019, 15, 2982–2989, doi:10.3762/bjoc.15.294

• described. Glycosylations were performed in CH2Cl2 and TMSOTf catalysis (Scheme 2). Galactofuranosyl iodide 5 was obtained by the treatment of per-O-TBS-β-ᴅ-Galf with a stoichiometric amount of TMSI, and glycosylated in situ by adding the acceptor in the presence of EtN(iPr)2 as acid scavenger (Scheme 3

A review of asymmetric synthetic organic electrochemistry and electrocatalysis: concepts, applications, recent developments and future directions

• Munmun Ghosh,
• Valmik S. Shinde and
• Magnus Rueping

Beilstein J. Org. Chem. 2019, 15, 2710–2746, doi:10.3762/bjoc.15.264

• mepivacaine (197a) [107]. The key steps in the synthesis involved the initial anodic oxidation of cyclic N-carbamate 194 bearing an 8-phenylmenthyl group as a chiral auxiliary which generates in situ N-acyliminium ion 195 and this 195 upon reaction with nucleophilic CN− in presence of catalytic TMSOTf and β

Chemical synthesis of the pentasaccharide repeating unit of the O-specific polysaccharide from Escherichia coli O132 in the form of its 2-aminoethyl glycoside

• Debasish Pal and
• Balaram Mukhopadhyay

Beilstein J. Org. Chem. 2019, 15, 2563–2568, doi:10.3762/bjoc.15.249

• ). Glycosylation of the known GlcNPhth acceptor 2 [12] and the rhamnosyl donor 3 [13] through the activation of thioglycoside using N-iodosuccinimide (NIS) in the presence of TMSOTf gave the Rha-(1→3)-GlcNPhth disaccharide 4 in 84% yield. The presence of a participating acetate group at the 2-position of the

• using NIS and TMSOTf afforded the trisaccharide 10 in 78% yield. The newly formed 1,2-cis glycosidic linkage was confirmed by the peaks at 4.27 ppm (d, J1′′,2′′ = 1.5 Hz, 1H, H-1′′) in the 1H NMR and at 93.8 ppm (C-1′′) in the 13C NMR spectra. The presence of the participating O-benzoyl group at the 6-O

• thioglycoside using NIS in the presence of TMSOTf at low temperature gave the disaccharide 16a (α) [1H NMR: 5.37 ppm (bs, 1H, H-1′), 13C NMR: 108.2 ppm (C-1′)] and 16b (β) [1H NMR: 5.36 ppm (d, J1′,2′ = 4.0 Hz, 1H, H-1′), 13C NMR: 95.6 ppm (C-1′)] in 89% yield (α:β = 2:1) (Scheme 3). Although the acceptor is

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• trimethylsilyl trifluoromethanesulfonate (TMSOTf) in a diastereoselective and stepwise manner. This novel methodology provides a shorter access to the intermediate 97, which is a key intermediate for the synthesis of triptolide. Recently, photoredox catalysis has emerged as a powerful and high-yielding method

Solid-phase synthesis of biaryl bicyclic peptides containing a 3-aryltyrosine or a 4-arylphenylalanine moiety

• Iteng Ng-Choi,
• Àngel Oliveras,
• Lidia Feliu and
• Marta Planas

Beilstein J. Org. Chem. 2019, 15, 761–768, doi:10.3762/bjoc.15.72

• spectrometry analysis showed that the pNB group was removed under the Suzuki–Miyaura reaction conditions. To obtain the biaryl bicyclic peptide 1, the Boc group of cyclic peptidyl resin 5 was then removed under mild conditions using trimethylsilyl triflate (TMSOTf) in presence of 2,6-lutidine in CH2Cl2 (Scheme

• -Leu-OH, DIPCDI, Oxyma, DMF. (vi) Fmoc-Ala-OH, DIPCDI, Oxyma, DMF. (vii) Boc-Phe(4-BPin)-OH, DIPCDI, Oxyma, DMF, 3 h. (viii) Pd2(dba)3, P(o-tolyl)3, KF, DME/EtOH/H2O (9:9:2), MW, 120 °C, 30 min. (ix) TFA/H2O/TIS (95:2.5:2.5), 2 h. (x) TMSOTf, 2,6-lutidine, CH2Cl2. (xi) PyOxim, Oxyma, DIPEA, NMP, 24 h

• . (vi) Fmoc-Ala-OH, DIPCDI, Oxyma, DMF. (vii) Boc-Tyr(3-B(OH)2,Me)-OH, DIPCDI, Oxyma, DMF, 3 h. (viii) Pd2(dba)3, SPhos, KF, DME/EtOH/H2O (9:9:2), MW, 120 °C, 30 min. (ix) TFA/H2O/TIS (95:2.5:2.5), 2 h. (x) TMSOTf, 2,6-lutidine, CH2Cl2. (xi) PyOxim, Oxyma, DIPEA, NMP, 24 h. Synthesis of the biaryl

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

• with trimethylsilyl trifluoromethanesulfonate (TMSOTf) and a tertiary amine as base a broad range of pyridine derivatives was accessible (Scheme 3). According to its discoverer, we named this reaction Flögel pyridine synthesis [21]. The reaction is very flexible with respect to the employed

Design and synthesis of multivalent α-1,2-trimannose-linked bioerodible microparticles for applications in immune response studies of Leishmania major infection

• Chelsea L. Rintelmann,
• Tara Grinnage-Pulley,
• Kathleen Ross,
• Daniel E. K. Kabotso,
• Angela Toepp,
• Anne Cowell,
• Christine Petersen,
• Balaji Narasimhan and
• Nicola Pohl

Beilstein J. Org. Chem. 2019, 15, 623–632, doi:10.3762/bjoc.15.58

• allow for purification by FSPE of the mannosyl intermediates and to facilitate future automated syntheses to produce α-1,2-trimannose in appreciable quantities similar to previous efforts (Scheme 1) [11][47][51]. To synthesize the oligosaccharide, activation of TCA donor 3 with TMSOTf and glycosylation

Low-budget 3D-printed equipment for continuous flow reactions

• Jochen M. Neumaier,
• Amiera Madani,
• Thomas Klein and
• Thomas Ziegler

Beilstein J. Org. Chem. 2019, 15, 558–566, doi:10.3762/bjoc.15.50

• step reaction arrangement starting from pyranose 4 was set up. Scheme 4 shows this setup of a suitable cascade reaction in which DBU, trichloroacetonitrile and pyranose 4 were pumped through the first flow reactor (R1) followed by the addition of the alcohol and TMSOTf through the second reactor. Table

Convergent synthesis of the pentasaccharide repeating unit of the biofilms produced by Klebsiella pneumoniae

• Arin Gucchait,
• Angana Ghosh and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2019, 15, 431–436, doi:10.3762/bjoc.15.37

• -benzylidene-β-D-glucopyranoside (11) in 70% yield. Stereoselective glycosylation of compound 11 with D-mannose-derived ethyl 2-O-acetyl-3,4,6-tri-O-benzyl-1-thio-α-D-mannopyranoside (3) [14] in the presence of a combination of N-iodosuccinimide (NIS) and trimethylsilyl trifluoromethanesulfonate (TMSOTf) [22

• couple with the D-mannose-derived thioglycoside acceptor 6 in the presence of TMSOTf [35] to furnish phenyl (4,6-O-benzylidene-2,3-di-O-benzyl-β-D-mannopyranosyl)-(1→4)-(6-O-benzoyl-2,3-di-O-benzyl-α-D-glucopyranosyl)-(1→3)-4,6-O-benzylidene-2-O-benzyl-1-thio-α-D-mannopyranoside (19) in 45% yield. The

• trisaccharide thioglycoside 19 can now act as a glycosyl donor fulfilling the orthogonal glycosylation principle [36]. Stereoselective glycosylation of disaccharide acceptor 13 with the trisaccharide donor 19 in the presence of a combination of NIS and TMSOTf [22][23] resulted in the formation of

Syntheses and chemical properties of β-nicotinamide riboside and its analogues and derivatives

• Mikhail V. Makarov and
• Marie E. Migaud

Beilstein J. Org. Chem. 2019, 15, 401–430, doi:10.3762/bjoc.15.36

• mixtures [24]. In the Vorbrüggen version of the silyl Hilbert–Johnson method, trimethylsilyl trifluoromethanesulfonate (TMSOTf) is used as a Friedel–Crafts catalyst. The TMSOTf-mediated glycosylation of Nam (1a) with tetra-O-acetyl-β-D-ribofuranose was first proposed by Tanimori et al. in 2002 [29] (Scheme

• glycosylation (Figure 3). This intermediate is subsequently approached by Nam from the less hindered side. Subsequently, Franchetti et al. [30] modified the above TMSOTf-protocol by introducing the preliminary silylation of the amide group of Nam, a procedure based on the chemistry developed by Vorbrüggen [24

• -O-acetyl-β-D-ribofuranose (2a) or 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D-ribofuranose (2b) in the presence of TMSOTf in 1,2-dichloroethane solution to give protected NR+ derivatives as triflates 9a,b. Critically, a larger excess of TMSCl decreases reaction rates and lowers yields, as the silylation of

Unexpected loss of stereoselectivity in glycosylation reactions during the synthesis of chondroitin sulfate oligosaccharides

• Teresa Mena-Barragán,
• José L. de Paz and
• Pedro M. Nieto

Beilstein J. Org. Chem. 2019, 15, 137–144, doi:10.3762/bjoc.15.14

• DBU. The glycosylation reaction with 2-propanol using TMSOTf as Lewis acid at 0 ºC cleanly provided the β-isopropyl glycoside 13 in 65% yield. Interestingly, no α-anomer was detected in the reaction mixture. Finally, cleavage of the levulinyl group using hydrazine monohydrate in pyridine/acetic acid

• buffer afforded compound 2. With the required disaccharide building blocks in hand, the synthesis of tetrasaccharide 14β was attempted using catalytic TMSOTf in CH2Cl2 at 0 ºC (Scheme 4). After F-SPE, two spots were detected in the TLC analysis of the fluorous containing fraction, in addition to

• % of TMSOTf with respect to the donor, 0 ºC, CH2Cl2 as solvent). As mentioned before, it has been reported that cyclic protecting groups like 4,6-O-benzylidene acetals in GalNAc trichloroacetimidates lead to the formation of α/β mixtures in glycosylations involving GlcA acceptors [43][47]. However

6’-Fluoro[4.3.0]bicyclo nucleic acid: synthesis, biophysical properties and molecular dynamics simulations

• Sibylle Frei,
• Andrei Istrate and
• Christian J. Leumann

Beilstein J. Org. Chem. 2018, 14, 3088–3097, doi:10.3762/bjoc.14.288

• tricyclic sugars 3α/β were individually reacted with trimethylsilyl trifluoromethanesulfonate (TMSOTf) in order to produce the corresponding glycal 4. Surprisingly, apart from the desired glycal 4 its hydrolysis products 5α/β were produced as main side products. In the case of the α-tricyclic sugar 3α the

• ) TMSCF3, NaI, THF, 70 °C, 2 h, 71%; d) TMSCF3, NaI, THF, 70 °C, 4 h, 75%; e) TMSOTf, 2,6-lutidine, DCM, 0 °C to rt, 2 h, 41% (4), 39% (5α/β); f) TMSOTf, 2,6-lutidine, DCM, 0 °C to rt, 7 h, 58% (4), 29% (5α/β). Synthesis of the thymidine phosphoramidite building block 10. Reagents and conditions: a) i

• building block 16. Reagents and conditions: a) Ac2O, pyridine, 0 °C to rt, 17 h, 87%; b) N-benzoylcytosine, BSA, TMSOTf, ACN, 0 °C to rt, 3.5 h, 41%; c) HF-pyridine, DCM/pyridine 5:1, 0 °C, 15 min, 91%; d) i) CeCl3·7H2O, NaBH4, MeOH, −78 °C, 20 min; ii) Bz2O, DMF, rt, 7 h, 94%; e) DMTr-OTf, DCM/pyridine 1

Synthesis of α-D-GalpN₃-(1-3)-D-GalpN₃: α- and 3-O-selectivity using 3,4-diol acceptors

• Emil Glibstrup and
• Christian Marcus Pedersen

Beilstein J. Org. Chem. 2018, 14, 2805–2811, doi:10.3762/bjoc.14.258

• precious” and recoverable acceptor 9, which, however, would result in lower yields when compared to glycosylations using excess of donor. In the initial experiment, using TMSOTf as the catalyst in CH2Cl2 at 0 °C, a pleasingly 8:1 3/4-O ratio and a 10:1 α/β-selectivity with a 57% isolated yield of the