Inherent atomic mobility changes in carbocation intermediates during the sesterterpene cyclization cascade

• Hajime Sato,
• Takaaki Mitsuhashi,
• Mami Yamazaki,
• Ikuro Abe and
• Masanobu Uchiyama

Beilstein J. Org. Chem. 2019, 15, 1890–1897, doi:10.3762/bjoc.15.184

• 351-0198, Japan Graduate School of Pharmaceutical Sciences, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan 10.3762/bjoc.15.184 Abstract We previously showed that the regio- and stereoselectivity in terpene-forming reactions are determined by the conformations of the carbocation

• means high mobility, yellow means moderate mobility, and blue means static. TS: transition state. The regio- and stereoselectivity in quiannulatene and sesterfisherol biosynthesis are determined by the initial conformation of GFPP. Reaction mechanism of quiannulatene biosynthesis. GFPP: geranylfarnesyl

Application of chiral 2-isoxazoline for the synthesis of syn-1,3-diol analogs

• Juanjuan Feng,
• Tianyu Li,
• Jiaxin Zhang and
• Peng Jiao

Beilstein J. Org. Chem. 2019, 15, 1840–1847, doi:10.3762/bjoc.15.179

• subjected to silica gel chromatography. Compound 4 was used to determine the stereoselectivity of the cycloaddition step as well as for oxidation. Oxidation of the 2-isoxazoline 4 with Jones’ reagent gave a complicated mixture, in which the desired carboxylic acid was not observed (Scheme 2). The stepwise

Synthesis of a [6]rotaxane with singly threaded γ-cyclodextrins as a single stereoisomer

• Jason Yin Hei Man and
• Ho Yu Au-Yeung

Beilstein J. Org. Chem. 2019, 15, 1829–1837, doi:10.3762/bjoc.15.177

• elucidating the origin of the stereoselectivity in the synthesis of 6R. The 1H spectrum of 4R is generally similar to that of 6R and strong NOE cross peaks between the triazole and CB[6], and also Ha of the anthracene and CB[6] protons were observed (Figure S10 in Supporting Information File 1), confirming

N-(1-Phenylethyl)aziridine-2-carboxylate esters in the synthesis of biologically relevant compounds

• Iwona E. Głowacka,
• Aleksandra Trocha,
• Andrzej E. Wróblewski and
• Dorota G. Piotrowska

Beilstein J. Org. Chem. 2019, 15, 1722–1757, doi:10.3762/bjoc.15.168

• of chemical and configurational stability was achieved by introducing N,N-dibenzylserinals 4 [10]. Another important strategy of asymmetric synthesis relies on chiral auxiliaries, i.e., a specially selected homochiral part of a starting material governing the stereoselectivity of subsequent reactions

Synthesis of pyrrolo[1,2-a]quinolines by formal 1,3-dipolar cycloaddition reactions of quinolinium salts

• Anthony Choi,
• Rebecca M. Morley and
• Iain Coldham

Beilstein J. Org. Chem. 2019, 15, 1480–1484, doi:10.3762/bjoc.15.149

• types of products. Conclusion In conclusion, we have found that carboxylic ester and amide-stabilised anions derived from quinolinium salts react with arylidenemalononitriles and N-methylmaleimide to give adducts in good yields and with very high stereoselectivity (single isomer products were isolated

Fluorine-containing substituents: metabolism of the α,α-difluoroethyl thioether motif

• Andrea Rodil,
• Alexandra M. Z. Slawin,
• Nawaf Al-Maharik,
• Ren Tomita and
• David O’Hagan

Beilstein J. Org. Chem. 2019, 15, 1441–1447, doi:10.3762/bjoc.15.144

• with very similar outcomes. In order to explore the stereoselectivity of this sulfoxidation, sulfoxide 11 isolated from the C. elegans incubation was analysed by chiral HPLC (IC column, solvent: 5% isopropanol in hexane; 1 mL/min). This was compared to a racemic reference sample of 11 prepared by

Borylation and rearrangement of alkynyloxiranes: a stereospecific route to substituted α-enynes

• Ruben Pomar Fuentespina,
• José Angel Garcia de la Cruz,
• Gabriel Durin,
• Victor Mamane,
• Jean-Marc Weibel and
• Patrick Pale

Beilstein J. Org. Chem. 2019, 15, 1416–1424, doi:10.3762/bjoc.15.141

• the reaction. Indeed, the bulkier the boron substituent is, the more efficient is the process. Therefore, the substitution at the boron plays a key role, most probably at the boron rearrangement step (see below). Stereoselectivity, scope and limitations Next, the stereoselectivity of this

• existence of at least one concerted step during the reaction mechanism. This step most probably corresponds to the group transfer in organoboron derivatives, as the stereoselectivity of such transfer has been demonstrated [32][33]. Regarding the oxiranyllithium stereochemical integrity and stability, it has

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

• stereoselectivity in the hydroboration reaction we hypothesized the transition states bearing to the two epimers. We assumed that borane would react firstly with the free hydroxy group generating an intermediate alkoxyborane, and that the hydroboration reaction occurs intramolecularly on such intermediate. Based on

Enantioselective Diels–Alder reaction of anthracene by chiral tritylium catalysis

• Qichao Zhang,
• Jian Lv and
• Sanzhong Luo

Beilstein J. Org. Chem. 2019, 15, 1304–1312, doi:10.3762/bjoc.15.129

• the observed stereoselectivity are provided in Supporting Information File 1, Figure S3. Conclusion In summary, we have introduced a new motif of chiral weakly coordinating Fe(III)-based bisphosphate anion for high performance asymmetric carbocation Lewis acid catalysis. The introduction of a metal

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

• intermediate was far away from the chiral steroidal nucleus. A better stereoselectivity was reported by Bruttomesso et al. in their work on the Ugi four-component reaction (Ugi-4CR) with a steroidal aldehyde, in which the carbonyl group was directly linked at the steroidal framework [16]. As shown in Scheme 2

• to be conducted at reflux to obtain a good yield of Ugi-derived steroids, albeit the procedure generated a pair of diastereomers (epimeric at C-5) in almost equal amount. The stereoselectivity of the intramolecular MCR increased when a bulky isonitrile was used, e.g., diethyl phosphonate isocyanide

Ugi reaction-derived prolyl peptide catalysts grafted on the renewable polymer polyfurfuryl alcohol for applications in heterogeneous enamine catalysis

• Alexander F. de la Torre,
• Gabriel S. Scatena,
• Oscar Valdés,
• Daniel G. Rivera and
• Márcio W. Paixão

Beilstein J. Org. Chem. 2019, 15, 1210–1216, doi:10.3762/bjoc.15.118

• produced by means of an initial Ugi reaction followed by an acid-catalyzed polymerization. They catalytic polymers were screened in the heterogeneous catalytic Michael addition in batch, proving that catalyst 3 is more effective and provides better stereoselectivity. A continuous-flow organocatalytic

Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids

• Herman O. Sintim,
• Hamad H. Al Mamari,
• Hasanain A. A. Almohseni,
• Younes Fegheh-Hassanpour and
• David M. Hodgson

Beilstein J. Org. Chem. 2019, 15, 1194–1202, doi:10.3762/bjoc.15.116

• by slow warming to ≈−10 °C before work-up. Finally, the reaction displayed remarkable stereoselectivity, in that the electrophile was introduced on ostensibly the more hindered face of the enolate (that is, cis (“contrasteric”) [24] to the unenolised ester group). The former observation was

• rationalisation of stereoselectivity [17][18][19]. Tartrate alkylation with a non-activated alkyl iodide. Alkylated tartrate to diazoester sequence. TES protection approach to the squalestatin core. Tartrate acetonide methylation. Tartrate alkylation with various alkyl halides. Rationalisation of dialkylation

Stereo- and regioselective hydroboration of 1-exo-methylene pyranoses: discovery of aryltriazolylmethyl C-galactopyranosides as selective galectin-1 inhibitors

• Alexander Dahlqvist,
• Axel Furevi,
• Niklas Warlin,
• Hakon Leffler and
• Ulf J. Nilsson

Beilstein J. Org. Chem. 2019, 15, 1046–1060, doi:10.3762/bjoc.15.102

• -terminal CRD), -7, -8C, -8N, -9C, and -9N. Results and Discussion Chemistry The synthesis starts from the known enol ethers 2, 4, and 6 prepared using published methods [25][26]. Hydroborations of enol ethers have been known to give good to excellent regio- and stereoselectivity and are thus a possible

• analog 6 to β-7 in high yield and with excellent stereoselectivity [31]. In none of the reaction conditions 1-methyl glycopyranoside side products were formed (Scheme 1). Continuing the synthesis towards (aryltriazolyl)methyl galactopyranosyl derivatives, the 2-deoxygalactoheptulose 3 was mesylated with

A diastereoselective approach to axially chiral biaryls via electrochemically enabled cyclization cascade

• Hong Yan,
• Zhong-Yi Mao,
• Zhong-Wei Hou,
• Jinshuai Song and
• Hai-Chao Xu

Beilstein J. Org. Chem. 2019, 15, 795–800, doi:10.3762/bjoc.15.76

• stereoselectivity of the reaction was not controlled by relative thermodynamic stability of the diastereomers. The major isomer of 3c, which contained a sterically less demanding Ph group at the R1 position (cf. Table 1), did not isomerize at room temperature for 1 year. However, heating a solution of this compound

• in MeCN at 80 °C for 4 h resulted in a mixture of diastereomers in a ratio of 3:1. These results suggest that the sterically demanding substituents at R1 and R2 positions (cf. Table 1) are critical to ensure good stereoselectivity during the product formation and to prevent isomerization after the

Diastereo- and enantioselective preparation of cyclopropanol derivatives

• Marwan Simaan and
• Ilan Marek

Beilstein J. Org. Chem. 2019, 15, 752–760, doi:10.3762/bjoc.15.71

• (or amination) sequence on achiral nonfunctionalized cyclopropenes provided the desired cyclopropanol (and cyclopropylamine) derivatives in excellent diastereo- and enantiomeric excesses. Keywords: carbocupration; cyclopropanol; cyclopropene; regioselectivity; stereoselectivity; Introduction The

• usually proceeds through single-electron transfer to dioxygen, leading to either a loss of stereoselectivity, degradation of the organocopper or to the formation of dimer as major products [71]. Therefore, it was clear that a different approach for the oxidation process was needed. Oxenoid, possessing the

Influence of per-O-sulfation upon the conformational behaviour of common furanosides

• Alexey G. Gerbst,
• Vadim B. Krylov,
• Dmitry A. Argunov,
• Maksim I. Petruk,
• Arsenii S. Solovev,
• Andrey S. Dmitrenok and
• Nikolay E. Nifantiev

Beilstein J. Org. Chem. 2019, 15, 685–694, doi:10.3762/bjoc.15.63

• pyranosides [10][11] and thus the effects of substitution in them are more complex. The conformational effects underlay the striking stereoselectivity in the glycosylation reaction by furanosyl donors [12]. Conformational analysis of furanosides includes both conformation of the furanoside ring and

Selectivity in multiple multicomponent reactions: types and synthetic applications

• Ouldouz Ghashghaei,
• Francesca Seghetti and
• Rodolfo Lavilla

Beilstein J. Org. Chem. 2019, 15, 521–534, doi:10.3762/bjoc.15.46

• , symmetrical adducts or polymers; ii) structurally preorganized systems allowing the generation of macrocycles and iii) selective processes in which a determined combination arises in a sequential manner, either directly or indirectly, through functional group deprotection/generation. Stereoselectivity (where

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