An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• stereochemistry of the product can be modulated by changing the stereochemical structure of the disulfide catalyst [10]. The simple reaction mechanism is shown in Scheme 4a. Thiyl radicals, which are generated under irradiation, trigger the reaction by adding to the methylenecyclopropane 4, which affords the

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

• isoxazolidines by means of dihydroxylation [9][10] and epoxidation [11][12] reactions. Regarding the stereochemistry, almost all of the realized additions proceed with an excellent trans stereoselectivity relative to the substituent at C-3, giving isoxazolidine-4,5-diols and isoxazolidinyl epoxides with a C-3/4

• lower values (2.08–3.30 ppm), and the signal for the H-5 proton can be found at 5.50 ppm due to the effect of the two oxygen atoms bound to the C5 carbon atom. Regarding the stereochemistry, the borane attack on the C=C double bond of the 2,3-dihydroisoxazole occurs from the sterically less hindered

• stereochemical results are consistent with our previous findings on the direct dihydroxylation and epoxidation reactions of 4,5-unsubstituted 2,3-dihydroisoxazoles [9][10][11][12]. To invert the relative C-3/4-trans stereochemistry, the isoxazolidin-4-ols 5a–c were first oxidized to the corresponding ketones

[3 + 2] Cycloaddition with photogenerated azomethine ylides in β-cyclodextrin

• Margareta Sohora,
• Leo Mandić and
• Nikola Basarić

Beilstein J. Org. Chem. 2020, 16, 1296–1304, doi:10.3762/bjoc.16.110

• the macrocyclic host affected the stereochemistry of the reaction. Moreover, we studied photodecarboxylation reactions initiated by the phthalimide chromophore [17][18][19] and applied them in cyclizations with memory of chirality [20] and diastereoselective peptide cyclizations [21

Palladium-catalyzed regio- and stereoselective synthesis of aryl and 3-indolyl-substituted 4-methylene-3,4-dihydroisoquinolin-1(2H)-ones

• Valeria Nori,
• Antonio Arcadi,
• Armando Carlone,
• Fabio Marinelli and
• Marco Chiarini

Beilstein J. Org. Chem. 2020, 16, 1084–1091, doi:10.3762/bjoc.16.95

• -assisted cyclization and reductive elimination from the resulting σ-indolylpalladium complex C (Scheme 5). The reaction led to the stereoselective formation of indole derivatives 6ba–fc (aryl, heteroaryl and vinyl groups were allowed in substrates 5) in good to high yield. The stereochemistry of compounds

Suzuki–Miyaura cross coupling is not an informative reaction to demonstrate the performance of new solvents

• James Sherwood

Beilstein J. Org. Chem. 2020, 16, 1001–1005, doi:10.3762/bjoc.16.89

• catalysed carbon–carbon bond formation, making it an obvious case study to validate the performance of novel solvents [1][2][3][4][5][6][7]. The polarity of the solvent is known to determine the structure and activity of catalytic intermediates, the rate determining step, and stereochemistry (where

Diversity-oriented synthesis of 17-spirosteroids

• Benjamin Laroche,
• Thomas Bouvarel,
• Martin Louis-Sylvestre and
• Bastien Nay

Beilstein J. Org. Chem. 2020, 16, 880–887, doi:10.3762/bjoc.16.79

• structure and stereochemistry of the products were determined by 2D NMR analysis. Taking 16b as an example, the key NOESY correlations between proton H-4' at 2.79 ppm and steroid protons H-12 at 1.33/1.65 ppm demonstrated that H-4' is on the α-face of the cyclohexene (Figure 3a). The endo character of the

• -ethynyl-17-hydroxysteroids 1–4 (top) and how they could be used to generate diversity (down). Structure of metathesis catalysts. Rationale for the observed stereochemistry: (a) NOESY correlations observed on compound 16b, showing key correlations between protons of the cyclohexene α-face and both protons

Efficient synthesis of dipeptide analogues of α-fluorinated β-aminophosphonates

• Marcin Kaźmierczak and
• Henryk Koroniak

Beilstein J. Org. Chem. 2020, 16, 756–762, doi:10.3762/bjoc.16.69

• Herein, we present an efficient synthesis of dipeptide analogues of α-fluorinated β-aminophosphonates. Each step of the synthesis was optimized to provide excellent yields. Moreover, the absolute configuration of the obtained compounds was determined by X-ray analysis, which proved the stereochemistry

• enzyme binding may depend on the C–F stereochemistry, the synthesis of such compounds with a specific configuration is very important [9][10][11]. α-Fluorinated phosphonates can be prepared by many different protocols [12][13][14][15][16]. Nucleophilic fluorination is one of the fundamental reactions in

• at room temperature. What is more, we attempted to crystallize at least one derivative to confirm the absolute stereochemistry of the obtained compounds. In order to obtain a single crystal suitable for X-ray diffraction studies, various crystallization techniques were tested [37][38

Combining enyne metathesis with long-established organic transformations: a powerful strategy for the sustainable synthesis of bioactive molecules

• Valerian Dragutan,
• Ileana Dragutan,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2020, 16, 738–755, doi:10.3762/bjoc.16.68

• the respective dienic compounds (Scheme 2) [52]. The reaction course is essential for directing the process towards the desired exo or endo isomer, in compliance with the required stereochemistry of the final product. For the intermolecular enyne metathesis reaction, the double bond of the alkene is

• contrast to the majority of steroids that are trans-fused, rhodexin A comprises cis-fused AB and CD rings. By carefully selecting the reaction conditions, they managed to impose this stereochemistry in all synthetic steps participating in the construction of the tetracyclic ring system of rhodexin A

Recent advances in Cu-catalyzed C(sp³)–Si and C(sp³)–B bond formation

• Balaram S. Takale,
• Ruchita R. Thakore,
• Elham Etemadi-Davan and
• Bruce H. Lipshutz

Beilstein J. Org. Chem. 2020, 16, 691–737, doi:10.3762/bjoc.16.67

• to products reflecting a complete inversion of stereochemistry. The screening showed that XPhos-Pd-G2 is the best pre-catalyst for these reactions and it was proposed that the reaction takes place through an SE2 pathway due to coordination of the carbonyl group of the nucleophile to the boronate

Synthesis of organic liquid crystals containing selectively fluorinated cyclopropanes

• Zeguo Fang,
• Nawaf Al-Maharik,
• Peer Kirsch,
• Matthias Bremer,
• Alexandra M. Z. Slawin and
• David O’Hagan

Beilstein J. Org. Chem. 2020, 16, 674–680, doi:10.3762/bjoc.16.65

• isomer 11b for subsequent analysis. Stereoisomer 11a was a crystalline solid and a suitable crystal was subject to X-ray structure analysis and the structure is shown in Scheme 4. In this way the stereochemistry of 11a and 11b could be confirmed unambiguously. Evaluation of liquid crystal candidates 8

• of the parameter was relatively low (Δε = −1.1). Thus the two isomers constitute two different classes of LC materials, entirely as a consequence of stereochemistry. The best compound of this series is 11a and it was of interest to get some insight into its conformational flexibility. Thus, a

• stereochemically clean sample of isomer 11b for experimental evaluation, theory predicts that it will have a modest negative dielectric value, indicating the importance of stereochemistry in dictating the class of LC material. We conclude too that the overall performance of prototype LCs 11a and 11b should not be

Towards the total synthesis of chondrochloren A: synthesis of the (Z)-enamide fragment

• Jan Geldsetzer and
• Markus Kalesse

Beilstein J. Org. Chem. 2020, 16, 670–673, doi:10.3762/bjoc.16.64

• (Cmc5) by the groups of Höfle and Reichenbach in 2003 [12]. This PKS/NRPS-derived natural product shows only weak antibiotic effects in agar diffusion tests against Micrococcus luteus, Schizosaccharomyces pombe, Bacillus subtilis and Staphylococcus aureus [12]. The relative and absolute stereochemistry

Absolute configurations of talaromycones A and B, α-diversonolic ester, and aspergillusone B from endophytic Talaromyces sp. ECN211

• Ken-ichi Nakashima,
• Junko Tomida,
• Takao Hirai,
• Yoshiaki Kawamura and
• Makoto Inoue

Beilstein J. Org. Chem. 2020, 16, 290–296, doi:10.3762/bjoc.16.28

•  4b). This is the first experimental evidence that corroborates the absolute configurations of 3 and 4, compounds that were reported previously without evidence for this stereochemistry. We also obtained single crystals of glauconic acid (5) as prisms by slow evaporation in CH2Cl2/n-hexane at 10 °C. X

Combination of multicomponent KA² and Pauson–Khand reactions: short synthesis of spirocyclic pyrrolocyclopentenones

• Riccardo Innocenti,
• Elena Lenci,
• Gloria Menchi and
• Andrea Trabocchi

Beilstein J. Org. Chem. 2020, 16, 200–211, doi:10.3762/bjoc.16.23

• reduced gauche interactions [55]. Subsequent epoxidation at the double bond directed by the hydroxy group and using m-chloroperbenzoic acid allowed to install two additional stereocenters with complete control of the relative stereochemistry in 68% yield. Such two-step synthesis proved to proceed also in

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

• Katarzyna Włodarczyk,
• Piotr Borowski and
• Marek Stankevič

Beilstein J. Org. Chem. 2020, 16, 88–105, doi:10.3762/bjoc.16.11

• reaction. In the presence of a Brønsted acid, mainly [1,3]-rearrangement is observed, whereas a Lewis acid catalyzes the [1,4]-sulfur migration. To gain insight into the mechanism of these transformations, the stereochemistry of these rearrangements have been tested, along with the conduction of some

• control experiments and DFT calculations. Keywords: Brønsted and Lewis acids; DFT; mechanistic studies; rearrangement; stereochemistry; sulfur atom migration; Introduction Among all organic reactions, rearrangements are an exciting class of transformations where unusual or even unexpected products can

Functionalization of the imidazo[1,2-a]pyridine ring in α-phosphonoacrylates and α-phosphonopropionates via microwave-assisted Mizoroki–Heck reaction

• Damian Kusy,
• Agata Wojciechowska,
• Joanna Małolepsza and
• Katarzyna M. Błażewska

Beilstein J. Org. Chem. 2020, 16, 15–21, doi:10.3762/bjoc.16.3

• of the desired products were formed. The structures of products 3 and 6–22 were confirmed by spectroscopic methods, 1H, 13C, 31P NMR, and MS analysis. The stereochemistry of the newly formed double bond was evaluated by 1H NMR spectroscopy. Next, we determined the influence of the position of a

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

• HMBC analysis, which was particularly useful in the cases in which only one product was detected. For example, for compound 14α, correlations between signals corresponding to H-1' and C-3 and between C-1' and H-3 were observed. The stereochemistry of the newly formed glycosidic linkages was established

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

• Eric J. N. Helfrich,
• Geng-Min Lin,
• Christopher A. Voigt and
• Jon Clardy

Beilstein J. Org. Chem. 2019, 15, 2889–2906, doi:10.3762/bjoc.15.283

• . Using enantiotopically doubly 13C-2H-labeled substrates, it is possible to determine the stereochemistry of a cyclization product by locating the 2H atom and its relative position to other stereocenters [75]. In vitro terpene biosynthesis, however, might not always result in the production of the

• , simply by rationally mutating the active-site residues. The majority of bacterial type II diterpene TCs produce bicyclic labdane, halimadane, or clerodane skeletons with different stereochemistry, levels of unsaturation, and hydroxylation patterns [124], which undergo further conversion with their

1,5-Phosphonium betaines from N-triflylpropiolamides, triphenylphosphane, and active methylene compounds

• Vito A. Fiore,
• Chiara Freisler and
• Gerhard Maas

Beilstein J. Org. Chem. 2019, 15, 2603–2611, doi:10.3762/bjoc.15.253

• XRD analysis (vide supra), the stereochemistry at the P-substituted olefinic bond could be determined in all cases from characteristic chemical shifts of the olefinic proton and from 3J(P,H) and 3J(P,C) coupling constants. The olefinic proton signal of the E-isomers was found in the δ range 6.8–7.7

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

• from E. coli O132 is accomplished in the form of its 2-aminoethyl glycoside. The 2-aminoethyl glycoside is particularly important as it allows further glycoconjugate formation utilizing the terminal amine without affecting the stereochemistry of the reducing end. The target was achieved through a [3

• manipulations on the commercially available monosaccharides and stereoselective chemical glycosylations. The 2-aminoethyl glycoside at the reducing end will facilitate further glycoconjugate formation without hampering the stereochemistry of the anomeric center. We have used similar glycosides in case of other

• Discussion It is important to select a suitable glycoside at the reducing end of the target oligosaccharide keeping in mind that the glycoside should allow further glycoconjugate formation without disturbing the stereochemistry of the anomeric center. Therefore, the 2-aminoethyl glycoside was selected at the

Synthesis of novel sulfide-based cyclic peptidomimetic analogues to solonamides

• José Brango-Vanegas,
• Luan A. Martinho,
• Lucinda J. Bessa,
• Andreanne G. Vasconcelos,
• Alexandra Plácido,
• Alex L. Pereira,
• José R. S. A. Leite and
• Angelo H. L. Machado

Beilstein J. Org. Chem. 2019, 15, 2544–2551, doi:10.3762/bjoc.15.247

• sequence displayed by 9e and 9h, the stereochemistry of the Phe residue is detrimental to the antihemolytic activity; (3) in a similar sense, for 9f and 9g, diastereosiomers on the Ile residue, the L-configuration on this residue is necessary to the observed hemolysis inhibition by S. aureus. Conclusion A

Chiral terpene auxiliaries V: Synthesis of new chiral γ-hydroxyphosphine oxides derived from α-pinene

• Anna Kmieciak and
• Marek P. Krzemiński

Beilstein J. Org. Chem. 2019, 15, 2493–2499, doi:10.3762/bjoc.15.242

• hydrolyzed with a 5% aqueous solution of NaOH. GC analysis of the isolated alcohol confirmed the presence of (1R,4S,5R)-apopinenol (18) and (1R,4R,5R)-16 in a ratio of 79.5:20.5. The structures and stereochemistry of both diastereomeric alcohols 16 and 18 were confirmed by 2D NMR spectra. All protons in 16

Self-assembled coordination thioether silver(I) macrocyclic complexes for homogeneous catalysis

• Zhen Cao,
• Aline Lacoudre,
• Cybille Rossy and
• Brigitte Bibal

Beilstein J. Org. Chem. 2019, 15, 2465–2472, doi:10.3762/bjoc.15.239

• diastereoisomers by coordination which had different geometries. Thereafter, the silver(I) complexes are discussed with the proposed stoichiometry from X-ray and NMR data, without accounting for stereochemistry: M2L2 for AgOTf and AgOTFA complexes (1a,b), M6L4 for AgNO3 one (1c) and M2L complex with PPh3AgOTf (1d

Indium-mediated C-allylation of melibiose

• Christian Denner,
• Manuel Gintner,
• Hanspeter Kählig and
• Walther Schmid

Beilstein J. Org. Chem. 2019, 15, 2458–2464, doi:10.3762/bjoc.15.238

• of this post-transition metal for the elongation of carbohydrates [3][4][5]. Additional contributions were reported in the literature by Paquette and co-workers concerning indium-mediated reactions in water and their stereochemistry [6][7]. Based on these findings this elongation method has been

In water multicomponent synthesis of low-molecular-mass 4,7-dihydrotetrazolo[1,5-a]pyrimidines

• Irina G. Tkachenko,
• Sergey A. Komykhov,
• Vladimir I. Musatov,
• Svitlana V. Shishkina,
• Viktoriya V. Dyakonenko,
• Vladimir N. Shvets,
• Mikhail V. Diachkov,
• Valentyn A. Chebanov and
• Sergey M. Desenko

Beilstein J. Org. Chem. 2019, 15, 2390–2397, doi:10.3762/bjoc.15.231

• the final confirmation of the structure and to establish the relative stereochemistry of both stereoisomers. NOESY cross-peaks between signals of NH and OH protons revealed that A and B are in fact stereoisomers, rejecting the regioisomeric structure 14’. The different 3J values between 6-H and 7-H

Current understanding and biotechnological application of the bacterial diterpene synthase CotB2

• Ronja Driller,
• Daniel Garbe,
• Norbert Mehlmer,
• Monika Fuchs,
• Keren Raz,
• Dan Thomas Major,
• Thomas Brück and
• Bernhard Loll

Beilstein J. Org. Chem. 2019, 15, 2355–2368, doi:10.3762/bjoc.15.228

• generate a vast number of (poly)cyclic hydrocarbon scaffolds. Remarkably, this complex chemical reaction, comprising changes in bonding, hybridization as well as the introduction of specific stereochemistry, is performed in a single reaction cascade without consumption of a cofactor [11]. In this review we