Metal-free glycosylation with glycosyl fluorides in liquid SO₂

• Krista Gulbe,
• Jevgeņija Lugiņina,
• Edijs Jansons,
• Artis Kinens and
• Māris Turks

Beilstein J. Org. Chem. 2021, 17, 964–976, doi:10.3762/bjoc.17.78

• mannosyl fluoride α-1a was achieved and the desired O-mannoside 3a was isolated in a high yield and α-selectivity. Hemiacetal α-4 was isolated as the only side-product formed via glycosyl donor hydrolysis with the water present in commercial SO2 [62]. To note, at lower temperatures (Table 1, entry 1) no

• the yield of mannoside 3b formed from a less reactive secondary alcohol 2b, various additives were tested (Table 1, entries 7–9). Presence of basic molecular sieves (4 Å) as a drying agent led to lower yield and did not suppress the formation of hemiacetal α-4 (Table 1, entry 7), while no reaction was

• -phenylethanol (2a) was carried out in pure conventional solvents (MeCN, THF, toluene or DCM) often used for glycosylation, no reaction was observed (Table 2, entries 1, 4, 6 and 9). Only traces of mannoside 3a and/or hemiacetal α-4 were detected by NMR spectroscopy in the presence of H3PO4 as a protic acid

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• hemiacetal 168 was shown to react with benzene in the presence of a Lewis acid or H2SO4 to form compounds 169–172 in various amounts, depending on the acid used (Scheme 41) [103]. It is assumed that an oxygen-stabilized α-(trifluoromethyl)carbenium ion is involved. It was shown that 168 could also react with

• (hetero)arenes [104][105] and alkenes [106] under Lewis acid activation but also with electron-rich arenes under thermal activation [107][108][109]. CF3-substituted hemiacetal 168 can react with amines to furnish the corresponding hemiaminal ethers, which can be further activated by a Lewis acid to

• generate CF3-substituted iminium ions able to promote Friedel–Crafts alkylations [110][111]. Ma et al. exploited this mode of activation in a Brønsted acid-catalyzed three-component asymmetric reaction [112]. Mixing hemiacetal 175, arylaniline 176, and indole derivatives 149 in the presence of a catalytic

Antibacterial scalarane from Doriprismatica stellata nudibranchs (Gastropoda, Nudibranchia), egg ribbons, and their dietary sponge Spongia cf. agaricina (Demospongiae, Dictyoceratida)

• Cora Hertzer,
• Stefan Kehraus,
• Nils Böhringer,
• Fontje Kaligis,
• Robert Bara,
• Dirk Erpenbeck,
• Gert Wörheide,
• Till F. Schäberle,
• Heike Wägele and
• Gabriele M. König

Beilstein J. Org. Chem. 2020, 16, 1596–1605, doi:10.3762/bjoc.16.132

• cyclopropyl ring H2-22 (δ −0.06 brt, J = 4.8 Hz, δ 0.43 dd, J = 3.9, 9.2 Hz). Furthermore, this spectrum proved the presence of the olefinic proton H-16 (δ 5.49 brs), the downfield shifted methine proton H-11 (δ 5.49 brs), and the hemiacetal hydrogen atom H-19 (δ 5.24 d, J = 4.4 Hz). The 1H NMR spectrum also

• -methylenedeoxoscalarin was determined. It needs to be noted that the molecule was unstable over time, especially in ring E, and a variety of degradation products formed by, inter alia, hydrolysis of the hemiacetal and loss of the acetoxy groups. The new scalarane was also detected in Doriprismatica stellata egg ribbons

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• generate an O,S-hemiacetal 72. Under the basic conditions, the hemiacetal 72 converted to the thiolate 74, which underwent an intramolecular substitution to give the final product thietanylbenzimidazolone 75 [46] (Scheme 16). 2.2.2 Synthesis via the stepwise nucleophilic displacements: Besides the double

Synthesis of C-glycosyl phosphonate derivatives of 4-amino-4-deoxy-α-ʟ-arabinose

• Lukáš Kerner and
• Paul Kosma

Beilstein J. Org. Chem. 2020, 16, 9–14, doi:10.3762/bjoc.16.2

• -arabinopyranoside (1), available in multigram amounts, was benzylated in 79% yield using benzyl bromide and sodium hydride in DMF, followed by hydrolysis of the anomeric aglycon of 2 with 5 M HCl and SrCl2 in acetic acid, which afforded the hemiacetal 3 as a 2:3 α/β anomeric mixture in 60% yield (Scheme 1

A green, economical synthesis of β-ketonitriles and trifunctionalized building blocks from esters and lactones

• Daniel P. Pienaar,
• Kamogelo R. Butsi,
• Amanda L. Rousseau and
• Dean Brady

Beilstein J. Org. Chem. 2019, 15, 2930–2935, doi:10.3762/bjoc.15.287

• example, in sugars, hemiacetal pyranoses (due to reduced bond angle strain) are energetically much more favored in solution compared to the corresponding 5-membered furanoses [17]. Significantly, 1H (500 MHz) and 13C NMR (126 MHz) of the purified product 6 (pure by TLC) indicated traces of what appears to

Anomeric sugar boronic acid analogues as potential agents for boron neutron capture therapy

• Daniela Imperio,
• Erika Del Grosso,
• Silvia Fallarini,
• Grazia Lombardi and
• Luigi Panza

Beilstein J. Org. Chem. 2019, 15, 1355–1359, doi:10.3762/bjoc.15.135

• position. The analogues were obtained by hydroboration of proper open-chain terminal alkenes that, after quenching with water, spontaneously afforded cyclic boronic acids with hemiacetal-like structures. Keywords: antitumor agents; boron neutron capture therapy; boronic acid; hydroboration; sugar analogue

Steroid diversification by multicomponent reactions

• Leslie Reguera,
• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Daniel G. Rivera

Beilstein J. Org. Chem. 2019, 15, 1236–1256, doi:10.3762/bjoc.15.121

• ]. In short, the organocatalytic conjugated addition of benzoylacetonitrile to cinnamaldehyde generates the hemiacetal 30, which next initiates the multicomponent sequence upon condensation with the aniline and formation of the imine, eventually occurring as a stable cyclic aminal. The attack of the

Electrophilic oligodeoxynucleotide synthesis using dM-Dmoc for amino protection

• Shahien Shahsavari,
• Dhananjani N. A. M. Eriyagama,
• Bhaskar Halami,
• Vagarshak Begoyan,
• Marina Tanasova,
• Jinsen Chen and
• Shiyue Fang

Beilstein J. Org. Chem. 2019, 15, 1116–1128, doi:10.3762/bjoc.15.108

• protected with the 2-cyanoethyl group. These protecting groups and the linker have to be cleaved under strongly basic and nucleophilic conditions. As a result, many sensitive groups including acetal, hemiacetal, vinyl ethers, enol ethers, aldehydes, esters, activated esters, thioesters, aziridines, epoxides

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

• -glucopyranoside (16) in 65% yield together with some 1,2-trans glycosylated product (≈10%), which was separated by column chromatography. Compound 16 was treated with palladium chloride [21] to give the disaccharide hemiacetal derivative 17 in 75% yield, which on treatment with trichloroacetonitrile in the

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• ) [53]. Starting from O-benzyl-D-serine (2S,3R)-2 was obtained in a similar way. Configurationally stable D-serinal derivative (R)-23 (prepared from D-serine [54]) which primarily exists as hemiacetal was subjected to cis-olefination with Stille's reagent at −30 °C to produce (S)-24 in good yield

Anomeric modification of carbohydrates using the Mitsunobu reaction

• Julia Hain,
• Patrick Rollin,
• Werner Klaffke and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2018, 14, 1619–1636, doi:10.3762/bjoc.14.138

• Mitsunobu reaction can also be profitably utilized for the anomeric modification of carbohydrates. Hence, we have focused this review on the utilization of the Mitsunobu reaction for manipulations of the carbohydrate hemiacetal, where reducing (anomerically unprotected) sugars react as the alcohol component

• hand, the equilibrium between the azodicarboxylate, the phosphine, and the acidic component, Nu-OH, is important (cf. Scheme 2, left dashed box). On the other hand, mutarotation of the sugar hemiacetal has to be discussed to predict the stereochemical outcome of the reaction. Mutarotation results in an

• cannot be regarded as a classical secondary alcohol group but as a hemiacetal OH, it can be successfully involved in Mitsunobu reactions to achieve 1-O-acyl glycoses. Thus, searching for an efficient protocol for the preparation of complex, multifunctional glycosyl esters in the context of the total

Lanyamycin, a macrolide antibiotic from Sorangium cellulosum, strain Soce 481 (Myxobacteria)

• Lucky S. Mulwa,
• Rolf Jansen,
• Dimas F. Praditya,
• Kathrin I. Mohr,
• Patrick W. Okanya,
• Joachim Wink,
• Eike Steinmann and
• Marc Stadler

Beilstein J. Org. Chem. 2018, 14, 1554–1562, doi:10.3762/bjoc.14.132

• (5.6 Hz) and 5.95 ppm (5.4 Hz) and thus fully establishing the hemiacetal amide structural part. The mean value of the coupling constants between H-26 and H-25 remained as 5.7 Hz for 1 and 6.4 Hz for 2 indicating both compounds were epimers at C-26. Accordingly, 13C and 1H shift differences between

A stereoselective and flexible synthesis to access both enantiomers of N-acetylgalactosamine and peracetylated N-acetylidosamine

• Bettina Riedl and
• Walther Schmid

Beilstein J. Org. Chem. 2018, 14, 856–860, doi:10.3762/bjoc.14.71

• cleaved by the use of acidic ion exchange (DOWEX H+). Subsequent ozonolysis caused the formation of the aldehyde by the oxidation of the methylene functionality. Consequently, intramolecular hemiacetal formation resulted immediately in the cyclization of the unprotected azido sugar, which was

Stimuli-responsive oligonucleotides in prodrug-based approaches for gene silencing

• Françoise Debart,
• Christelle Dupouy and
• Jean-Jacques Vasseur

Beilstein J. Org. Chem. 2018, 14, 436–469, doi:10.3762/bjoc.14.32

Gram-scale preparation of negative-type liquid crystals with a CF₂CF₂-carbocycle unit via an improved short-step synthetic protocol

• Tatsuya Kumon,
• Shohei Hashishita,
• Takumi Kida,
• Shigeyuki Yamada,
• Takashi Ishihara and
• Tsutomu Konno

Beilstein J. Org. Chem. 2018, 14, 148–154, doi:10.3762/bjoc.14.10

• addition reaction, a Michael addition reaction, giving rise to the corresponding magnesium enolate Int-L. The subsequent hydrolysis of Int-L then leads to the γ-hydroxyketone 8a', which easily tautomerizes into the more stable 5-membered hemiacetal 8a. From the above insight into the reaction mechanism, if

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

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

• isomerized in the presence of an Ir complex and the resulting prop-1-enyl group was then removed by aqueous iodine to yield hemiacetal 30 which was stereoselectively phosphorylated by reaction with lithium hexamethyldisilazide (LHMDS), and subsequent treatment with tetrabenzyl pyrophosphate. Final

• 62 (Scheme 8) [118]. To this end, GlcN hemiacetal 61 was reduced by treatment with NaBH4, the acetamido group was removed with barium hydroxide, and the resulting amine was transformed into azide 62. The primary alcohol in 62 was regioselectively protected as silyl ether, followed by benzylation and

An efficient synthesis of a C₁₂-higher sugar aminoalditol

• Łukasz Szyszka,
• Anna Osuch-Kwiatkowska,
• Mykhaylo A. Potopnyk and
• Sławomir Jarosz

Beilstein J. Org. Chem. 2017, 13, 2146–2152, doi:10.3762/bjoc.13.213

• was the liberation of the anomeric position (C1), which, as we noticed, can cause problems. We subjected azide 4 to acetolysis and, although this reaction is very capricious in higher sugar chemistry [7][8], succeeded in the preparation of the desired hemiacetal acetate 5 in very good yield (86%) as 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

• ]. The displacement of the anomeric hydroxy group of a glycosyl hemiacetal by an acceptor for dehydrative glycosylation is an interesting alternative as glycosyl hemiacetals are often undesired side products in glycosylation reactions due to the competitive reaction with trace amounts of water present in

• the reaction mixture. The Gin group established a preactivation glycosylation procedure using glycosyl hemiacetals [36]. As an example, the hemiacetal donor 21 was preactivated with Tf2O and diphenyl sulfoxide (Ph2SO) at −40 °C. This was followed by the addition of the acceptor isopropyl alcohol

• to afford the corresponding glycosyl amide 26. Two possible reaction pathways have been proposed for this dehydrative glycosylation (Scheme 7) [37]. Upon mixing diphenyl sulfoxide and triflic anhydride, diphenyl sulfide bis(triflate) (27) is formed in situ (Scheme 7a). In pathway 1, hemiacetal 28

Intramolecular glycosylation

• Xiao G. Jia and
• Alexei V. Demchenko

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

• the hemiacetal product 99. Crossover experiments with 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose acceptor showed only disaccharides resulting from the intramolecular glycosylation. However, when crossover experiments with cyclohexanol were conducted, the intermolecularly formed cyclohexyl glycoside

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

• building block 8 followed by UV-cleavage, disaccharide 16 was obtained in 63% isolated yield. Moreover, DBDMH performs as well as N-iodosuccinimide (NIS) in activating phenyl selenoglycoside 17 in the presence of water to furnish hemiacetal 18 en route to glycosyl imidate 19 (Scheme 2). Conclusion The

Are boat transition states likely to occur in Cope rearrangements? A DFT study of the biogenesis of germacranes

• José Enrique Barquera-Lozada and
• Gabriel Cuevas

Beilstein J. Org. Chem. 2017, 13, 1969–1976, doi:10.3762/bjoc.13.192

• hemiacetal group (TS1b-2). This could be because the hemiacetalization reduces the transannular distance between C10 and C5 (3.20 Å, 2.91 Å, 2.72 Å and 2.66 Å for 1b, 4, 5 and 6, respectively) that facilitates orbital interactions and bond formation. The chair TS (TS6-3) is still more stable, the energy

• 2’ from 1, as in case of 2, is thermodynamically forbidden. Epimer 2’ can also produce a hemiacetal (3’) but this compound has a higher energy than 3 by 4.2 kcal/mol; this is due to the C5 propenyl group in 3’ is axially oriented instead of equatorially as in 3. In contrast to 3, the formation of

• epimer 3’ from 1 is not thermodynamically highly favored. Therefore, the hemiacetal formation with the right orientation is fundamental to produce an elemanolide more stable than the (Z,E)-germacranolide. It has been proposed that the configuration of an elemane depends on the most stable conformation of

The chemistry and biology of mycolactones

• Matthias Gehringer and
• Karl-Heinz Altmann

Beilstein J. Org. Chem. 2017, 13, 1596–1660, doi:10.3762/bjoc.13.159

Sugar-based micro/mesoporous hypercross-linked polymers with in situ embedded silver nanoparticles for catalytic reduction

• Qing Yin,
• Qi Chen,
• Li-Can Lu and
• Bao-Hang Han

Beilstein J. Org. Chem. 2017, 13, 1212–1221, doi:10.3762/bjoc.13.120

• . As the prepared porous polymer SugPOP-1 is based on hemiacetal glucose, Ag nanoparticles (AgNPs) can be successfully incorporated into the polymer by an in situ chemical reduction of freshly prepared Tollens’ reagent. The obtained AgNPs/SugPOP-1 composite demonstrates good catalytic activity in the

• porous polymer SugPOP-1 is based on hemiacetal glucose, it was further postfunctionalized to embed the AgNPs into the material using an in situ chemical reduction of the freshly prepared Tollens’ reagent. The related catalytic reduction by the AgNPs/SugPOP-1 composite was also explored at room

• porous polymers containing a hemiacetal glucose motif (SugPOP-1), AgNPs were smoothly embedded into the material by chemical reduction of freshly prepared Tollens’ reagent, allowing in situ formation of AgNPs in the polymer matrix. With a high porosity and micro-/mesoporous features, the AgNP-loaded

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

• steps from known galactosylazide selenide 23 [29]. Acetylation of the C3 hydroxy group of 23 furnished fully differentially protected selenoglycoside 24 in 82% yield. Hydrolysis of the selenoglycoside using NIS in aqueous THF produced hemiacetal 25 that was silylated prior to selective saponification of

• the C3 O-acetate to yield building block 26 (Scheme 5). Fucosazide building block 8 was derived from diacetyl fucal 27 that in turn was prepared in two steps from L-fucose [30]. Azido-selenation of 27 and hydrolysis of the seleno fucosazide with NIS in aqueos THF [31] provided hemiacetal 28, which was