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

• yield with excellent stereoselectivity. The noteworthy features of the synthetic strategy are (a) incorporation of a β-D-mannosidic linkage and (b) late stage TEMPO-mediated oxidation of the primary hydroxy group into a carboxylic group after completion of glycosylations. The starting compound 2

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

• applicability, while most interesting developments in terms of synthetic efficiency, improved stereoselectivity and overall yields relate to the first approach. This approach, the synthetic glycosylation conditions depend on the nature of the sugar component. These conditions differ whether 1-halo-2,3,5-tri-O

• temperature. Because only the β-form of NR+ is of biochemical and medicinal relevance, any valuable method of synthesis of NR+ should offer a high level of β-stereoselectivity. Approaches based on the glycosylation of Nam will be discussed first and will be followed by a review of the NR+ syntheses

• riboside anomers were synthesized, with the best β/α-anomer stereoselectivity obtained when the chloride form of the sugars were used as precursors. Thus, the reaction between Nam (1a) and 2,3,5-tri-O-acetyl-D-ribofuranosyl chloride (3a) in acetonitrile at 0 °C yielded the triacetylated product 4a mainly

Reusable and highly enantioselective water-soluble Ru(II)-Amm-Pheox catalyst for intramolecular cyclopropanation of diazo compounds

• Hamada S. A. Mandour,
• Yoko Nakagawa,
• Masaya Tone,
• Hayato Inoue,
• Nansalmaa Otog,
• Ikuhide Fujisawa,
• Soda Chanthamath and
• Seiji Iwasa

Beilstein J. Org. Chem. 2019, 15, 357–363, doi:10.3762/bjoc.15.31

• determined to be (1S,5R,6R) by single-crystal X-ray diffraction analysis (Supporting Information File 1) [51]. Since the stereoselectivity of products depends on the cis/trans geometry of the reactants, other stereoisomers such as the (1S,5R,6S) product was not formed in this catalytic cyclopropanation

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• rearrangement of cyclopropenylcarbinyl acetates, the observed stereoselectivity was explained by invoking a chair-like transition state model TS4 in which the aryl group preferentially occupies a pseudo-equatorial orientation (Scheme 11) [48]. Although the presence of a halogen atom was tolerated, as

Application of olefin metathesis in the synthesis of functionalized polyhedral oligomeric silsesquioxanes (POSS) and POSS-containing polymeric materials

• Patrycja Żak and
• Cezary Pietraszuk

Beilstein J. Org. Chem. 2019, 15, 310–332, doi:10.3762/bjoc.15.28

• involves CM of OVS with carboranylstyrene compounds with different substituents (Ph, Me, or H, Scheme 6) [16]. The reactions catalyzed by Ru-1, occurred with quantitative conversion and excellent regio- and stereoselectivity leading to exclusive formation of E-isomers. However, CM was accompanied by a

• of the type of olefin used, under optimized conditions all reactions proceeded with high yields and stereoselectivity, leading to exclusive formation of the E,E-isomer. Marciniec reported the synthesis of divinylgermasilsesquioxane (DDSQ-2GeVi) and proved effective functionalization of such compounds

• via cross metathesis; b) synthesis of POSS-containing polymers via acyclic diene metathesis; c) synthesis of POSS-containing copolymers via ROMP. Cross metathesis of OVS with terminal olefins (stereoselectivity as discussed in the text). Cross metathesis of OVS with substituted styrenes. Modification

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

• stereoselectivity of the cyclocondensation step is best explained by the attack on a re-face of the C=O group due to chelation of Zn2+ to the carbonyl oxygen and amide nitrogen/oxygen atoms [49]. A better approach in terms of carbon atom economy relied on the addition of allylmagnesium chloride to the aldehyde (R

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

• and D-glucuronic acid (GlcA) acceptors. These results, together with those obtained from experiments employing model monosaccharide building blocks, highlight the impact of the glycosyl acceptor structure on the stereoselectivity of glycosylation reactions. Our study provides useful data about the

• substitution pattern of GlcA units for the efficient synthesis of CS oligomers. Keywords: carbohydrate chemistry; chondroitin sulfate; glycosylation; oligosaccharide synthesis; stereoselectivity; Introduction Chondroitin sulfate (CS) is a highly heterogeneous polysaccharide, constituted by the repetition of

• -trifluroacetyl participating group at position 2. Our results provide data for the correct design of CS building blocks and highlight the influence of glycosyl acceptor reactivity on the stereoselectivity of glycosylation reactions even in the presence of 2-participating groups [33]. Results and Discussion We

Systematic synthetic study of four diastereomerically distinct limonene-1,2-diols and their corresponding cyclic carbonates

• Hiroshi Morikawa,
• Jun-ichi Yamaguchi,
• Shun-ichi Sugimura,
• Masato Minamoto,
• Yuuta Gorou,
• Hisatoyo Morinaga and
• Suguru Motokucho

Beilstein J. Org. Chem. 2019, 15, 130–136, doi:10.3762/bjoc.15.13

• oxide) and conditions, the desired diastereomers were synthesised in moderate to high yields with, in most cases, high stereoselectivity. Comparison of the NMR data of the obtained diols and carbonates revealed that the four different diastereomers of each compound could be distinguished by reference to

• conditions with high diastereomeric stereoselectivity and, in most cases, moderate to high yields. To compare the four LMdiols and the four LM5CCs, a set of the characteristic analytical data such as melting points, optical rotation values and Kovats retention index values in gas chromatography was listed in

Asymmetric synthesis of a high added value chiral amine using immobilized ω-transaminases

• Antonella Petri,
• Valeria Colonna and
• Oreste Piccolo

Beilstein J. Org. Chem. 2019, 15, 60–66, doi:10.3762/bjoc.15.6

• point to evaluate the reactivity and stereoselectivity of the enzymes in the transamination reaction of substrate 1 and the results are reported in Table 1. As can be seen in Table 1, ATA-025-IMB was the most efficient among the (R)-selective enzymes since it led to high conversion and enantiomeric

Selective ring-opening metathesis polymerization (ROMP) of cyclobutenes. Unsymmetrical ladderphane containing polycyclobutene and polynorbornene strands

• Yuan-Zhen Ke,
• Shou-Ling Huang,
• Guoqiao Lai and
• Tien-Yau Luh

Beilstein J. Org. Chem. 2019, 15, 44–51, doi:10.3762/bjoc.15.4

• backbone in 14 may influence the stereoselectivity of the polynorbornene strand in 7 during the course of ROMP. Conclusion In summary, we have demonstrated useful ROMP conditions to selectively transform cyclobutene derivatives into the corresponding polycyclobutenes in THF at 0 °C, whereas the

Stereodivergent approach in the protected glycal synthesis of L-vancosamine, L-saccharosamine, L-daunosamine and L-ristosamine involving a ring-closing metathesis step

• Pierre-Antoine Nocquet,
• Aurélie Macé,
• Frédéric Legros,
• Jacques Lebreton,
• Gilles Dujardin,
• Sylvain Collet,
• Arnaud Martel,
• Bertrand Carboni and
• François Carreaux

Beilstein J. Org. Chem. 2018, 14, 2949–2955, doi:10.3762/bjoc.14.274

• the syn diastereomer 18 in high stereoselectivity (93:7). After silylation of the free hydroxy group, the cleavage of the PMB ether with DDQ led to alcohol 20 in 77% yield for the two steps. Ring-closing metathesis of diene 21, obtained by O-vinylation of 20, gave the dihydropyran 22 in 53% overall

Generation of 1,2-oxathiolium ions from (arysulfonyl)- and (arylsulfinyl)allenes in Brønsted acids. NMR and DFT study of these cations and their reactions

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov,
• Olesya V. Khoroshilova and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2018, 14, 2897–2906, doi:10.3762/bjoc.14.268

• halogenohydroxylation (Hal = I, Br) or addition–elemination of bromine (forming bromobutadienes) with high stereoselectivity [25][26]. Apart from that, reactions of sulfur containing allenes were studied in acidic media [27][28]. Despite promising results, there was no further research in this area. Based on our recent

Olefin metathesis catalysts embedded in β-barrel proteins: creating artificial metalloproteins for olefin metathesis

• Daniel F. Sauer,
• Johannes Schiffels,
• Takashi Hayashi,
• Ulrich Schwaneberg and
• Jun Okuda

Beilstein J. Org. Chem. 2018, 14, 2861–2871, doi:10.3762/bjoc.14.265

• the catalyst Ru-4 with the short linker, the activity of Ru-4@NB4exp dropped to TON = 3,000, even though the conjugation was almost quantitative [62]. However, this “influence” on the activity could not be transferred to the regio- and stereoselectivity of the polymer microstructure. Apart from ROMP

Synthesis of cis-hydrindan-2,4-diones bearing an all-carbon quaternary center by a Danheiser annulation

• Gisela V. Saborit,
• Carlos Cativiela,
• Ana I. Jiménez,
• Josep Bonjoch and
• Ben Bradshaw

Beilstein J. Org. Chem. 2018, 14, 2597–2601, doi:10.3762/bjoc.14.237

• stereoselectivity of the ring-formation step can be explained by the suprafacial addition of the allene to the double bond of the α,β-unsaturated compound 4, the diastereoselectivity being sterically controlled by the methyl group on the β-face. The transformation of the vinylsilane moiety in 5 into the

Some mechanistic aspects regarding the Suzuki–Miyaura reaction between selected ortho-substituted phenylboronic acids and 3,4,5-tribromo-2,6-dimethylpyridine

• Piotr Pomarański,
• Piotr Roszkowski,
• Jan K. Maurin,
• Armand Budzianowski and
• Zbigniew Czarnocki

Beilstein J. Org. Chem. 2018, 14, 2384–2393, doi:10.3762/bjoc.14.214

• transformation [22]. In such cases the stereoselectivity may depend on additional chelation effects [28][29][30][31][32][33][34]. Buchwald and co-workers reported an efficient stereoselective synthesis of axially chiral biarylamides by Pd–O bond formation during the oxidative addition step [28][29]. Also other

Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• and co-workers developed a cobalt-catalyzed hydroarylation of 2-vinyloxiranes with indoles 7 to form C2-allylated products 46, albeit in low stereoselectivity (Scheme 29b) [83]. Similarly, Cheng et al. reported a hydroarylation reaction of arenes 7 with a bicyclic alkene to form ring-opening products

Asymmetric Michael addition reactions catalyzed by calix[4]thiourea cyclohexanediamine derivatives

• Zheng-Yi Li,
• Hong-Xiao Tong,
• Yuan Chen,
• Hong-Kui Su,
• Tangxin Xiao,
• Xiao-Qiang Sun and
• Leyong Wang

Beilstein J. Org. Chem. 2018, 14, 1901–1907, doi:10.3762/bjoc.14.164

• convenience and good stereoselectivity [5][6]. Accordingly, different versions of this reaction have been extensively studied. Notably, the Michael addition reaction of 1,3-dicarbonyl compounds to conjugated nitroalkenes is very important for the synthesis of chiral nitro carbonyl compounds, such as bioactive

Recent advances in hypervalent iodine(III)-catalyzed functionalization of alkenes

• Xiang Li,
• Pinhong Chen and
• Guosheng Liu

Beilstein J. Org. Chem. 2018, 14, 1813–1825, doi:10.3762/bjoc.14.154

• applied in this reaction. A C(sp3)–I(III) intermediate 34, which was trapped by vicinal nitrogen nucleophiles to form the chiral syn-β-fluoroaziridine 33, was proposed. Both fluoroaziridines 33 and β-fluoropyrrolidines 36 were obtained in good yields and high anti-stereoselectivity. However, the reaction

• , the cinnamamide 41i could be transformed to the corresponding difluorination product 42i with excellent enantioselectivity and high stereoselectivity, albeit in moderate yields (Scheme 14, top) [64]. Inspired by the propensity for such anchimeric assistance in these reactions, an enantio- and

DFT calculations on the mechanism of copper-catalysed tandem arylation–cyclisation reactions of alkynes and diaryliodonium salts

• Tamás Károly Stenczel,
• Ádám Sinai,
• Zoltán Novák and
• András Stirling

Beilstein J. Org. Chem. 2018, 14, 1743–1749, doi:10.3762/bjoc.14.148

• the basis of the mechanism the origin of the stereoselectivity is ascribed to the interaction of the Cu ion with the oxazoline oxygen driving the ring-closure step selectively. Keywords: catalysis; DFT calculation; iodonium salts; reaction mechanism; tandem arylation–cyclisation; Introduction

• (Scheme 2, step 1). In the next step we compared the energetics of two different paths (paths A and B), to get insight into the order of the arylation and cyclisation steps. Additionally, the relevance of vinyl cation formation and the stereoselectivity were examined. The energy profiles start with the

• stereoselectivity of the reaction and it also excludes the formation of vinyl-cation intermediates. The obtained results could serve as a useful and more general description of the mechanism of the carboarylation–ring closure strategy based on the utilisation of alkynes and diaryliodonium salts, beyond the selected

β-Hydroxy sulfides and their syntheses

• Mokgethwa B. Marakalala,
• Edwin M. Mmutlane and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1668–1692, doi:10.3762/bjoc.14.143

• various aldehydes as shown in Scheme 21 [56]. It involved the reaction of a pre-prepared enantiopure toluene 70 with aromatic as well as aliphatic aldehydes in the presence of LDA. The stereoselectivity was in favor of the anti-diastereoisomer and was found to be dependent on the size of the aldehyde. It

• Fujisawa and co-workers in 1984 as depicted in Scheme 22 [57]. Coincidentally, the presence of the sulfenyl group at the α-position of the carbonyl center was found to be crucial for the stereoselectivity. Despite the sharp advancement in the field of biotechnology in the last decade, the application of

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

• this is important to explain and predict the stereoselectivity of anomeric modifications under Mitsunobu conditions. Though the Mitsunobu reaction is often not the first choice for the anomeric modification of carbohydrates, this review shows the high value of the reaction in many different

• circumstances. Keywords: anomeric stereoselectivity; carbohydrates; glycoside synthesis; Mitsunobu reaction; Introduction Fifty years ago, Oyo Mitsunobu reported a preparation of esters from alcohols and carboxylic acids supported by two auxiliary reagents, diethyl azodicarboxylate (DEAD) and

• dimethylformamide, has been shown to be influential in terms of efficacy and stereoselectivity [19]. Since its infancy, the Mitsunobu reaction has found applications in carbohydrate chemistry, as its broad scope and mild conditions are ideal for the formation of conjugates with sensitive natural products. Standard

Glycosylation reactions mediated by hypervalent iodine: application to the synthesis of nucleosides and carbohydrates

• Yuichi Yoshimura,
• Hideaki Wakamatsu,
• Yoshihiro Natori,
• Yukako Saito and
• Noriaki Minakawa

Beilstein J. Org. Chem. 2018, 14, 1595–1618, doi:10.3762/bjoc.14.137

• (OTf)2, Yb(OTf)3) and a Brønsted acid (TfOH) were proven useful as activators, by which the reaction finished in a short time and gave the products with high stereoselectivity [79]. Recently, the reaction was revisited by Kajimoto et al., who sought a glycosylation reaction that could be applied to

• /acetonitrile/isobutyronitrile/pivalonitrile greatly improved both the chemical yields and stereoselectivity, as shown in Scheme 21. The results suggested that both the solvent system and iodonium salt promoter are required for selectivity. Even though glycals have a π-electron-rich enol ether unit, reports

Enantioselective phase-transfer catalyzed alkylation of 1-methyl-7-methoxy-2-tetralone: an effective route to dezocine

• Ruipeng Li,
• Zhenren Liu,
• Liang Chen,
• Jing Pan and
• Weicheng Zhou

Beilstein J. Org. Chem. 2018, 14, 1421–1427, doi:10.3762/bjoc.14.119

• in C7 was crucial to guarantee the stereoselectivity. Meanwhile, the good catalysis was maintained with both dihydrocinchonidine-derived C14 and dehydro compound C15. Finally, the quaternary ammonium group from quinine was examined (Table 1, entries 16 and 17), and C16 and C17 gave the result

• stereoselectivity. For the screening of the base, the reduction of volume or concentration of 50% aq NaOH resulted in a decreased yield (Table 2, entries 11 and 12). If NaOH was replaced by K2CO3, no reaction took place (Table 2, entry 13). As far as the reaction temperature was concerned (Table 2, entry 7, 14 and

Recent applications of chiral calixarenes in asymmetric catalysis

• Mustafa Durmaz,
• Erkan Halay and
• Selahattin Bozkurt

Beilstein J. Org. Chem. 2018, 14, 1389–1412, doi:10.3762/bjoc.14.117

• corresponding (S,S)-40 as obtained without further separation of conformational isomers. Both the catalytic activity and the stereoselectivity were changed to different extents depending to the substituents on the calixarene skeleton. Best efficiencies and enantioselectivities were obtained when

• to 90%) but moderate diastereoselectivities (up to 65:35) were obtained (Scheme 26). A general organocatalyzed aldol reaction mechanism in water was suggested by the authors. Accordingly, the observed catalytic activity and stereoselectivity was explained by the formation of a hydrophobic and

• activity and stereoselectivity of catalyst 99. As shown in Figure 11, this catalytic system renders to use the calixarene cavity and in consequence of this both the high diastereoselectivity and enantioselectivity can be explained. Furthermore, when 99 used in 2 mol % can be recycled easily and re-used six

Synthesis of chiral 3-substituted 3-amino-2-oxindoles through enantioselective catalytic nucleophilic additions to isatin imines

• Hélène Pellissier

Beilstein J. Org. Chem. 2018, 14, 1349–1369, doi:10.3762/bjoc.14.114

• -isocupreine as organocatalyst instead of 15 mol % of β-isocupreidine (Scheme 11) in this reaction resulted in the formation of the corresponding (R)-configured products ent-36 with good to high enantioselectivities (83–95% ee) and moderate to good yields (37–79%), as shown in Scheme 12. The stereoselectivity