Acyclic cucurbit[n]uril bearing alkyl sulfate ionic groups

• Christian Akakpo,
• Peter Y. Zavalij and
• Lyle Isaacs

Beilstein J. Org. Chem. 2025, 21, 717–726, doi:10.3762/bjoc.21.55

• temperature overnight. Afterwards, the mixture was centrifuged (4400 rpm, 10 min) to pellet excess insoluble C1. An aliquot of the supernatant and a solution of dimethyl malonic acid as a non-binding internal standard of known concentration were transferred to an NMR tube followed by collection of a 1H NMR

• spectrum using a delay time between pulses of 20 seconds to ensure accurate integration. The inherent aqueous solubility of C1 was determined to be 3.97 mM by comparison of the integrals for Ha of C1 with that of the CH3-resonance for dimethyl malonic acid (Figure S5 in Supporting Information File 1

Origami with small molecules: exploiting the C–F bond as a conformational tool

• Patrick Ryan,
• Ramsha Iftikhar and
• Luke Hunter

Beilstein J. Org. Chem. 2025, 21, 680–716, doi:10.3762/bjoc.21.54

• compared to the non-fluorinated stearic acid 12 (Figure 3) [26]. If two fluorines are introduced into the middle of an alkyl chain in a 1,2-pattern, several competing factors arise that can influence the molecular conformation [27]. One factor is hyperconjugation: conformations in which the σ*C–F orbitals

• (III, Figure 11) [149]. These effects have been exploited to control the conformations of simple bioactive amines such as γ-aminobutyric acid (GABA, 86, Figure 11) [150][151][152][153][154][155]. GABA is a neurotransmitter that binds to a variety of different GABA receptors, and information about the

• protonated amine. These conformational changes alter the DNA-binding mode, such that the pyrrolidine NH groups of 95 now interact with the DNA phosphates rather than the bases or the sugars [164]. Progressing now to a six-membered ring system, consider the scaffold, pipecolic acid (96, Figure 11) [165][166

Asymmetric synthesis of fluorinated derivatives of aromatic and γ-branched amino acids via a chiral Ni(II) complex

• Maurizio Iannuzzi,
• Thomas Hohmann,
• Michael Dyrks,
• Kilian Haoues,
• Katarzyna Salamon-Krokosz and
• Beate Koksch

Beilstein J. Org. Chem. 2025, 21, 659–669, doi:10.3762/bjoc.21.52

• diastereomerically pure γ‑branched fluorinated amino acids. This work further underlines the importance of chiral Ni(II) complexes in the synthesis of fluorinated amino acids. Keywords: chiral nickel complexes; fluorinated amino acids; gram-scale amino acid synthesis; stereoselective synthesis; Introduction Non

• -natural amino acids are pivotal in protein engineering and drug development. Over 30% of approved small‑molecule drugs today contain non‑canonical amino acid building blocks [1][2]. In peptide and protein engineering, non‑natural amino acids significantly increase the respective range of tools used to

• hectogram range, is a major strength of this method. In this context, Han et al. could show that the trifluorinated variant of α-aminobutyric acid, trifluoroethylglycine (TfeGly), can be synthesized on a 100 g scale with great enantiomeric purity [8]. The critical step here is the alkylation of the Ni(II

Recent advances in allylation of chiral secondary alkylcopper species

• Minjae Kim,
• Gwanggyun Kim,
• Doyoon Kim,
• Jun Hee Lee and
• Seung Hwan Cho

Beilstein J. Org. Chem. 2025, 21, 639–658, doi:10.3762/bjoc.21.51

• field was achieved in 2016 by Yun and co-workers, who developed a copper-catalyzed regio- and enantioselective hydroallylation of vinylboronic acid pinacol esters (Bpin) and 1,8-diaminonaphthalene boramides (Bdan) 33 (Scheme 12) [53]. Subsequently, Hoveyda and co-workers introduced a complementary

Entry to 2-aminoprolines via electrochemical decarboxylative amidation of N‑acetylamino malonic acid monoesters

• Olesja Koleda,
• Janis Sadauskis,
• Darja Antonenko,
• Edvards Janis Treijs,
• Raivis Davis Steberis and
• Edgars Suna

Beilstein J. Org. Chem. 2025, 21, 630–638, doi:10.3762/bjoc.21.50

• 10.3762/bjoc.21.50 Abstract The electrochemical synthesis of 2-aminoprolines based on anodic decarboxylation–intramolecular amidation of readily available N-acetylamino malonic acid monoesters is reported. The decarboxylative amidation under Hofer–Moest reaction conditions proceeds in an undivided cell

• -disubstituted piperidine-containing amino acid subunits. Likewise, a cyano-substituted cyclic aminal is a core structural unit of the fibroblast activation protein inhibitor 5 [3] (Figure 1). The widespread use of non-proteinogenic cyclic amino acids in drug discovery justifies both the design of new analogs

• and the development of efficient synthetic methods to access these medicinally relevant structural motifs. Herein, we report an electrochemical synthesis of 2-aminoproline and 2-aminopipecolic acid derivatives 6 (Figure 1). Recently, we disclosed an electrochemical approach to tetrahydrofuran and

Photocatalyzed elaboration of antibody-based bioconjugates

• Marine Le Stum,
• Eugénie Romero and
• Gary A. Molander

Beilstein J. Org. Chem. 2025, 21, 616–629, doi:10.3762/bjoc.21.49

• different molecules, such as a drug and a targeting moiety. This technique has been shown to be useful in applications such as cell labeling, protein–protein interactions, and photoradiosynthesis of bioconjugates, but the most important challenge remains the lack of specificity to target one amino acid, and

• structures [38][39]. In 2021, Bottecchia and Noël reported the utility of photoredox catalysis for the functionalization of amino acid side chains, paving the way for tailored modifications in biotherapeutics [40]. More recently, Sato et al. have reviewed photochemical strategies enabled by a range of

• selectivity and the preservation of sensitive biological structures when appropriate redox potentials of photocatalysts are applied to the targeted amino acid. Additional advantages of photoinduced reactions include the ability to perform the reactions rapidly (typically <15 minutes). It was only in the late

Semisynthetic derivatives of massarilactone D with cytotoxic and nematicidal activities

• Rémy B. Teponno,
• Sara R. Noumeur and
• Marc Stadler

Beilstein J. Org. Chem. 2025, 21, 607–615, doi:10.3762/bjoc.21.48

• -UV system [column 2.1 × 50 mm, 1.7 μm, C18 Acquity UPLC BEH (Waters), solvent A: H2O + 0.1% formic acid; solvent B: ACN + 0.1% formic acid, gradient: 5% B for 0.5 min, increasing to 100% B in 19.5 min, maintaining 100% B for 5 min, RF = 0.6 mL/min, UV–vis detection 200–600 nm]. NMR spectra were

• ), solvent A: H2O + 0.1% formic acid; solvent B: acetonitrile (ACN) + 0.1% formic acid, gradient: 5% B for 0.5 min, increasing to 100% B in 20 min, maintaining isocratic conditions at 100% B for 10 min, flow = 0.6 mL/min, UV–vis detection 190–600 nm]. Preparative HPLC was achieved at room temperature on an

• Agilent 1100 series preparative HPLC system [ChemStation software (Rev. B.04.03 SP1); binary pump system; column: Kinetex 5u RP C18, dimensions 250 × 21.20 mm; mobile phase: ACN + 0.05% trifluoroacetic acid (TFA) and water + 0.05% TFA; flow rate: 20 mL/min; diode array UV detector; 226 fraction collector

Total synthesis of (±)-simonsol C using dearomatization as key reaction under acidic conditions

• Xiao-Yang Bi,
• Xiao-Shuai Yang,
• Shan-Shan Chen,
• Jia-Jun Sui,
• Zhao-Nan Cai,
• Yong-Ming Chuan and
• Hong-Bo Qin

Beilstein J. Org. Chem. 2025, 21, 601–606, doi:10.3762/bjoc.21.47

• dearomatization offers considerable versatility. Not only can it be employed under basic dearomatization conditions, but it is also effective under Lewis acid conditions. Combined with a reductive elimination using Zn/AcOH, the benzofuran skeleton can be easily synthesized. This dual applicability of the new

• 14 was performed next and the desired iodide was isolated and, to our delight, the cleavage of the MOM group occurred concomitantly, affording compound 15 in 75% yield. This reaction is likely triggered by the in situ-generated acid. As in our previously reported synthesis, a Zn/AcOH reductive

Sequential two-step, one-pot microwave-assisted Urech synthesis of 5-monosubstituted hydantoins from L-amino acids in water

• Wei-Jin Chang,
• Sook Yee Liew,
• Thomas Kurz and
• Siow-Ping Tan

Beilstein J. Org. Chem. 2025, 21, 596–600, doi:10.3762/bjoc.21.46

• Discussion As the first step of Urech hydantoin synthesis involved the N-carbamylation of amino acids, we carried out the microwave-assisted synthesis of urea derivatives in water, utilizing ʟ-phenylaniline as the representative amino acid. The optimal conditions for the N-carbamylation of ʟ-phenylaniline

• second step was attempted as part of a one-pot synthesis of hydantoins by the addition of concentrated hydrochloric acid followed by microwave irradiation of the reaction mixture at 80 °C for 15 min (Scheme 2). Gratifyingly, the acid-induced intra-cyclization of the urea derivative H1a proceeded smoothly

• amino acid. The hydantoins were found to be optically active (except for H2d), suggesting that enantiomeric information was preserved during the reaction (see Supporting Information File 1). Hydantoin yields (34–89%) are generally comparable to previously reported methods [7][8][9][10][11][12][13][14

Formaldehyde surrogates in multicomponent reactions

• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Bernhard Westermann

Beilstein J. Org. Chem. 2025, 21, 564–595, doi:10.3762/bjoc.21.45

• , several efforts have been made to improve the chemoselectivity of the oxidation step. Among the most relevant examples, o-iodoxybenzoic acid (IBX) has been used in Ugi and Passerini reactions to oxidize the suitable alcohol to the desired aldehyde [13]. Alternatively, catalytic amounts of a ternary system

• consequently, different catalytic strategies to afford the electrophilic addition on the final cyclization step. Finally, other examples show the synthesis of 3-aryl and alkyl quinoline-3-carboxylate derivatives under acid catalysis for the activation of DMSO via the Pummerer reaction (Scheme 10). In these

• was carried out via copper catalysis or iodine–acid catalysis. Interestingly, when aliphatic amines are employed (R3 = n-Pr, n-Bu, product 8) only the N atoms are incorporated in the structure of the final product, probably because the high temperature favors the elimination of the alkyl group. The

Study of the interaction of 2H-furo[3,2-b]pyran-2-ones with nitrogen-containing nucleophiles

• Constantine V. Milyutin,
• Andrey N. Komogortsev and
• Boris V. Lichitsky

Beilstein J. Org. Chem. 2025, 21, 556–563, doi:10.3762/bjoc.21.44

• target product was not obtained (Table 1, entries 3–5). Apparently, the presence of acid reagent is necessary for implementation of considered recyclization. In this regard we tried to perform the process under study using phenylhydrazine in salt form. Indeed, reflux of furanone 1a with the corresponding

• elaborated above for the preparation of enamines 4. Interaction of starting compound 1a with hydrazine was performed using acetic acid as a solvent at reflux for 8 h. As a result, the appropriate pyrazolone 10a, unsubstituted at both nitrogen atoms, was obtained with 73% yield (Scheme 5b). Based on the

• established by X-ray analysis. The proposed mechanism of the considered processes is outlined at Scheme 8. Initially, the free nitrogen nucleophile is reversibly generated from the corresponding hydrochloride or acetate. Next, acid-catalyzed addition of the amine component to the carbon atom of the aroyl

Binding of tryptophan and tryptophan-containing peptides in water by a glucose naphtho crown ether

• Gianpaolo Gallo and
• Bartosz Lewandowski

Beilstein J. Org. Chem. 2025, 21, 541–546, doi:10.3762/bjoc.21.42

• peptides [4][5]. Tryptophan also serves as a substrate to produce hormones such as serotonin or melatonin [6][7]. Due to the biological relevance of tryptophan synthetic receptors for this amino acid are highly sought after [8]. From a biological perspective it is especially desirable to achieve selective

• binding of tryptophan in water [9]. However, the development of selective amino acid receptors in aqueous environments is challenging since it requires a combination of hydrophobic and polar interactions for binding [10][11][12]. As a result, the number of reported selective receptors for tryptophan in

• aqueous media is limited (Figure 1a–c) [13][14][15][16][17][18]. In particular, receptors which bind tryptophan residues in peptides are rare [19][20]. Recently, we developed a glucose-based naphtho crown ether 1 (Figure 1d) which binds amino acid methyl esters with aromatic side chains chemoselectively

Vinylogous functionalization of 4-alkylidene-5-aminopyrazoles with methyl trifluoropyruvates

• Judit Hostalet-Romero,
• Laura Carceller-Ferrer,
• Gonzalo Blay,
• Amparo Sanz-Marco,
• José R. Pedro and
• Carlos Vila

Beilstein J. Org. Chem. 2025, 21, 533–540, doi:10.3762/bjoc.21.41

• starting materials to study the vinylogous functionalization with alkyl trifluoropyruvates. The synthesis of compounds 3 was accomplished by the reaction of cyclic ketones 1 and 5-aminopyrazoles 2 in the presence of acetic acid (Scheme 1) [30][31]. Cyclohexenones 1a–c provided the corresponding products

Cryptophycin unit B analogues

• Thomas Schachtsiek,
• Jona Voss,
• Maren Hamsen,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2025, 21, 526–532, doi:10.3762/bjoc.21.40

• ] to obtain free acid 11. Exchange of the Boc protecting group of dimethylaniline 8 to an acryloyl substituent and subsequent saponification furnished dimethylamine building block 13. For the macrocycle assembly, especially the ring closure, we decided on two different routes. While the cryptophycin

• macrolactamisation [21]. The syntheses of required unit A [28], C [29][30], and D [31] building blocks were accomplished as described previously. tert-Butyl-protected leucic acid 14 and Fmoc-β-aminopivalic acid (15) were connected by Steglich esterification (Scheme 2) and after cleavage of the tert-butyl ester group

• , HOAt, N,N-dimethylformamide 0 °C for 2 h and at rt for 20 min, 11%; f) Grubbs II catalyst, CH2Cl2, reflux, 3 h, 84%; g) TFA, H2O, CH2Cl2, 0 °C to rt, 5 h, 91%. EDC·HCl = 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride; DMAP = 4-(dimethylamino)pyridine; TFA = trifluoroacetic acid; HOAt = 1

Deep-blue emitting 9,10-bis(perfluorobenzyl)anthracene

• Long K. San,
• Sebastian Balser,
• Brian J. Reeves,
• Tyler T. Clikeman,
• Yu-Sheng Chen,
• Steven H. Strauss and
• Olga V. Boltalina

Beilstein J. Org. Chem. 2025, 21, 515–525, doi:10.3762/bjoc.21.39

• , dried over 4 Å molecular sieves); quinine hemisulfate salt monohydrate (Fluka); sulfuric acid (EMD Chemicals); diethyl ether anhydrous (EMD Chemicals, ACS grade); chloroform-d (CDCl3, Cambridge Isotope Labs, 99.8%); hexafluorobenzene (C6F6, Oakwood Products); deionized distilled water (purified with a

Synthesis of the aggregation pheromone of Tribolium castaneum

• Biyu An,
• Xueyang Wang,
• Ao Jiao,
• Qinghua Bian and
• Jiangchun Zhong

Beilstein J. Org. Chem. 2025, 21, 510–514, doi:10.3762/bjoc.21.38

• (R)-citronellic acid [18], methyl (S)-3-hydroxy-2-methylpropanoate, (S)-2-methyl-1-butanol [19], (R)-2,3-O-isopropylideneglyceraldehyde [20], (R)- and (S)-citronellol [21], (R)-4-methyl-δ-valerolactone [22], porcine pancreatic lipase (PPL)-catalyzed acetylation of racemic citronellol [23], and Evan′s

• enolate of diethyl malonate yielded (S)-2-(hex-5-en-2-yl)malonate ((S)-6), and realized a stereospecific inversion of chiral secondary tosylate (R)-5 [30][31]. The geminal ester (S)-6 was next treated with NaOH in methanol to afford (S)-2-(hex-5-en-2-yl)malonic acid ((S)-7) in 96% yield [32]. Then

• , geminal acid (S)-7 was decarboxylated with DMSO to yield chiral acid (S)-8 [33], followed by TiCl4-catalyzed reduction with ammonia-borane to obtain the chiral alkenyl alcohol (S)-9 [34]. The final tosylation with p-tosyl chloride provided (S)-3-methylhept-6-en-1-yl 4-methylbenzenesulfonate ((S)-10) [29

Unprecedented visible light-initiated topochemical [2 + 2] cycloaddition in a functionalized bimane dye

• Metodej Dvoracek,
• Brendan Twamley,
• Mathias O. Senge and
• Mikhail A. Filatov

Beilstein J. Org. Chem. 2025, 21, 500–509, doi:10.3762/bjoc.21.37

• the chlorination reactions on the synthetic path to Cl2B and Me2B, chlorine gas was generated by reacting MnO₂ with HCl and then passed through a stirred suspension of the pyrazolinone. In the case of Me4B, trichloroisocyanuric acid (TCICA) was used as the chlorinating agent as a safer alternative to

Synthesis of N-acetyl diazocine derivatives via cross-coupling reaction

• Thomas Brandt,
• Pascal Lentes,
• Jeremy Rudtke,
• Michael Hösgen,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2025, 21, 490–499, doi:10.3762/bjoc.21.36

• benzylboronic acid gave the corresponding N-acetyl diazocine 17 (45%, Table 4). Interestingly, this reaction only took place if brominated N-acetyl diazocine 2 was used as starting material although iodoaryl compounds are in general more reactive [25]. The reaction of halogenated N-acetyl diazocines 2 and 3

• with bis(pinacolato)diboron did not lead to the formation of the pinacolborane-substituted N-acetyl diazocine 18. Accordingly, the Suzuki–Miyaura reaction with inversed roles between N-acetyl diazocine boronic acid pinacol ester and aryl or alkyl halides could not be investigated. The Buchwald–Hartwig

• . Using diphenylamine as a more electron-rich amine resulted in the formation of diphenylamino-substituted N-acetyl diazocine 20 in a significantly lower yield of 25% starting from the bromide 2 and 47% starting from the iodo precursor 3 (Table 5). Deprotection of carbamate 19 with trifluoroacetic acid

Synthesis of electrophile-tethered preQ₁ analogs for covalent attachment to preQ₁ RNA

• Laurin Flemmich and
• Ronald Micura

Beilstein J. Org. Chem. 2025, 21, 483–489, doi:10.3762/bjoc.21.35

• mild reduction with methanolic sodium borohydride. Upon purification by reversed-phase chromatography using aqueous hydrobromic acid as eluent (0.5% in H2O), a considerable fraction of the alcohols was already converted to the desired bromides 4c,d. Only in the case of 4b, no deoxygenative bromination

• was observed, and the alcohol intermediate was isolated in pure form. In both cases, quantitative bromination was achieved by heating the compounds in concentrated aqueous hydrobromic acid, which after evaporation afforded the pure compounds 4b–d. To generate iodide 4e, alcohol 11 was isolated and

• by displacement of the mesyl group to give a six-membered cyclic carbamate, a reactivity that has been described earlier [34]. Thus, care was taken to quickly isolate compound 14 and use it immediately in the next step. Deblocking of the secondary amine by treatment with trifluoroacetic acid afforded

Organocatalytic kinetic resolution of 1,5-dicarbonyl compounds through a retro-Michael reaction

• James Guevara-Pulido,
• Fernando González-Pérez,
• José M. Andrés and
• Rafael Pedrosa

Beilstein J. Org. Chem. 2025, 21, 473–482, doi:10.3762/bjoc.21.34

• ] using 20 mol % of catalyst A and 20 mol % of p-nitrobenzoic acid (PNBA) as co-catalyst in different solvents at room temperature. The results obtained are summarized in Scheme 3 and Table 1. The progress of the reaction was monitored using thin-layer chromatography (TLC) and 1H NMR analysis of the

• entry 2 versus entry 6 in Table 2). Furthermore, we studied the effect of using an organic acid as the co-catalyst for forming the enamine intermediate from 1 and for the retro-Michael reaction. We observed that benzoic acid (BA) as a co-catalyst provides a lower er than that achieved with PNBA as a co

• a one dm path length, and concentration was given in grams per 100 mL. TLC analysis was performed on glass-backed plates coated with silica gel 60 and an F254 indicator and visualized by either UV irradiation or staining with phosphomolybdic acid solution. Flash chromatography uses silica gel (230

Electrochemical synthesis of cyclic biaryl λ³-bromanes from 2,2’-dibromobiphenyls

• Andrejs Savkins and
• Igors Sokolovs

Beilstein J. Org. Chem. 2025, 21, 451–457, doi:10.3762/bjoc.21.32

• -[1,1'-biphenyl]-2-amines 3 with sodium nitrite and an acid under aqueous conditions. Recently, Wencel-Delord and co-workers disclosed an improved protocol toward diazonium intermediates 2 under non-aqueous conditions (t-BuONO and MsOH in acetonitrile) [4]. Nevertheless, the improved method still

New tandem Ugi/intramolecular Diels–Alder reaction based on vinylfuran and 1,3-butadienylfuran derivatives

• Yuriy I. Horak,
• Roman Z. Lytvyn,
• Andrii R. Vakhula,
• Yuriy V. Homza,
• Nazariy T. Pokhodylo and
• Mykola D. Obushak

Beilstein J. Org. Chem. 2025, 21, 444–450, doi:10.3762/bjoc.21.31

• insufficiently studied furo[2,3-f]isoindole derivatives. Ugi adducts formed from (E)-3-(furan-2-yl)acrylaldehyde, maleic acid monoanilide, isonitrile, and an amine spontaneously underwent the IMDAV reaction with a high level of stereoselectivity, leading to single pairs of enantiomers of 4,4a,5,6,7,7a-hexahydro

• construction [27][28]. For instance, the intramolecular Diels–Alder reactions of vinylarenes (IMDAV) strategy [29][30] has been used to synthesize annulated isoindoles, including thieno[2,3-f]isoindoles [31][32] and furo[2,3-f]isoindoles [33][34], from thienyl- or furylallylamines and unsaturated acid

• the Ugi reaction with a maleic acid to form adducts containing both, diene and dienophilic fragments. It was found that aldehyde 1a reacted with amines 2, isonitriles 3, and maleic acid monoanilide (4a) to form an adduct that spontaneously underwent a [4 + 2] cycloaddition giving furoisoindoles 5a–h

Beyond symmetric self-assembly and effective molarity: unlocking functional enzyme mimics with robust organic cages

• Keith G. Andrews

Beilstein J. Org. Chem. 2025, 21, 421–443, doi:10.3762/bjoc.21.30

• typically not possible for imine [314] or metal-coordination cages [156][202][365]. Further, the robust amide cages could withstand harsh conditions such as ester hydrolysis, allowing access to the key acid-functionalized cages [38] that mimic aspartyl proteases and glycoside hydrolases. Otte has employed

• there to be wide-ranging potential across low-symmetry cavity research [205][208][309][366][370][371][372][373][374] if new and more explicit emergent geometric rules can be codified and exploited [39]. We were also able to statistically access a cage with a single internal carboxylic acid group and

• more than 104 compared to the background rate (298 K, CDCl3) (Figure 9B) [41]. Here, the strongly preorganized pair of carboxylic acids split duties: one covalently activates an acyl group while the other provides bifunctional acid/base activation. Together, they bind the transition state

Identification and removal of a cryptic impurity in pomalidomide-PEG based PROTAC

• Bingnan Wang,
• Yong Lu and
• Chuo Chen

Beilstein J. Org. Chem. 2025, 21, 407–411, doi:10.3762/bjoc.21.28

• product on HPLC even for the reaction of diethylene glycolamine and 1. Capping the free hydroxy group with a methyl group improved the separation on HPLC marginally. However, incorporating a clickable propargyl group greatly benefited separation. Similar to the alcohol, amino-PEG5-acid also reacted with 1

The effect of neighbouring group participation and possible long range remote group participation in O-glycosylation

• Rituparna Das and
• Balaram Mukhopadhyay

Beilstein J. Org. Chem. 2025, 21, 369–406, doi:10.3762/bjoc.21.27

• . performed glycosylations under solvent-free conditions with poorly reactive disarmed per-O-acetylated (15) and per-O-benzoylated (18) glycosyl donors on being activated in air aided by catalytic amounts of a mild promoter, methanesulphonic acid (Scheme 3) [92]. The ester group was capable of conjugating

• . Levulinoyl protection: Levulinic acid (Lev, 27) as protecting group which can be cleaved using hydrazine hydrate in AcOH, also yields highly selective 1,2-trans glycosides [95][96] and was implemented as a substitute for acetyl or benzoyl protection [97][98]. van Boom et al. also showed the use of a masked

• demonstrated that the use of triflimide (Tf2NH) in solvents like CH2Cl2, acetonitrile or toluene at −78 °C yielded exclusively the 1,2-trans stereoselective glycoside product 105 (protocol A, Scheme 18), while the use of triflic acid (TfOH) in ether as the solvent at ambient temperature conditions (protocol B