Hydroquinone–pyrrole dyads with varied linkers

• Hao Huang,
• Christoffer Karlsson,
• Maria Strømme,
• Martin Sjödin and
• Adolf Gogoll

Beilstein J. Org. Chem. 2016, 12, 89–96, doi:10.3762/bjoc.12.10

• % yield after 3 h. When the reaction was performed at room temperature, only 20% yield was obtained after 48 h. Close to equal quantities of cis-4c and trans-4c were formed in this reaction, and were separated chromatographically. Having access to both isomers was desirable, since the stereoisomers are

Organocatalytic and enantioselective Michael reaction between α-nitroesters and nitroalkenes. Syn/anti-selectivity control using catalysts with the same absolute backbone chirality

• Jose I. Martínez,
• Uxue Uria,
• Maria Muñiz,
• Efraím Reyes,
• Luisa Carrillo and
• Jose L. Vicario

Beilstein J. Org. Chem. 2015, 11, 2577–2583, doi:10.3762/bjoc.11.277

• despite the advances made in the field, an important challenge arises when a molecule containing multiple stereocentres has to be prepared because the access to all possible stereoisomers is not usually straightforward. While obtaining one or other mirror image of the target molecule can also be easily

[2.2]Paracyclophane derivatives containing tetrathiafulvalene moieties

• Laura G. Sarbu,
• Lucian G. Bahrin,
• Peter G. Jones,
• Lucian M. Birsa and
• Henning Hopf

Beilstein J. Org. Chem. 2015, 11, 1917–1921, doi:10.3762/bjoc.11.207

• -dithiolium salts; [2.2]paracyclophane; regioselective bromination; stereoisomers; tetrathiafulvalenes; Introduction Tetrathiafulvalene (TTF) and its derivatives have been extensively studied with respect to their applications as organic metals and superconductors [1][2]. These properties are a consequence

• a mixture of inseparable isomeric tetrathiafulvalenes 7 in 17% yield. Since compound 6 already exhibits planar chirality (racemate Rp/Sp), the theoretical number of stereoisomers of the tetrathiafulvalene 7 should be six as follows: cis-(Sp,Sp) with cis-(Rp,Rp) and trans-(Sp,Sp) with trans-(Rp,Rp

Cross metathesis of unsaturated epoxides for the synthesis of polyfunctional building blocks

• Meriem K. Abderrezak,
• Kristýna Šichová,
• Nancy Dominguez-Boblett,
• Antoine Dupé,
• Zahia Kabouche,
• Christian Bruneau and
• Cédric Fischmeister

Beilstein J. Org. Chem. 2015, 11, 1876–1880, doi:10.3762/bjoc.11.201

• performances (Table 1, entries 7 and 8). Similarly, the cross metathesis of 1 with acrylonitrile was conducted to furnish the bifunctional derivative 3 in 71% yield as a mixture of stereoisomers. In that case, high conversions and yields could only be obtained by means of slow addition of the catalyst and high

• dilution (Scheme 2) [13]. As we already observed, [13][14][22] together with other groups, [35][36] in various cross metathesis reactions involving acrylonitrile, the cross metathesis product 3 was obtained as a mixture of E (minor) and Z (major) stereoisomers. With these two compounds in hands, we turned

Mechanism, kinetics and selectivity of selenocyclization of 5-alkenylhydantoins: an experimental and computational study

• Biljana M. Šmit,
• Radoslav Z. Pavlović,
• Dejan A. Milenković and
• Zoran S. Marković

Beilstein J. Org. Chem. 2015, 11, 1865–1875, doi:10.3762/bjoc.11.200

• addition of PhSeCl to the double bond, is presented in Scheme 1, while the 5-exo pathway with all stereoisomers is presented in Scheme 2. The first step of the proposed mechanism producing the seleniranium cation, followed by anti-attack of the external nucleophile (Cl−) to the double bond [35] of 5

Preparative semiconductor photoredox catalysis: An emerging theme in organic synthesis

• David W. Manley and
• John C. Walton

Beilstein J. Org. Chem. 2015, 11, 1570–1582, doi:10.3762/bjoc.11.173

• yield of 75%. Phenyl- and 2-thienylacetic acids afforded adducts accompanied by the dimers bibenzyl (18%) and 1,2-di(thiophen-2-yl)ethane (27%), respectively. Significantly, Boc-protected α-amino acids also proved amenable and yielded adducts as 1:1 mixtures of stereoisomers. Chirality was not preserved

Cathodic hydrodimerization of nitroolefins

• Michael Weßling and
• Hans J. Schäfer

Beilstein J. Org. Chem. 2015, 11, 1163–1174, doi:10.3762/bjoc.11.131

• the Marple electrode and converted to SCE. Hydrodimerization of nitroalkene 14 and 15. (a) Intramolecular hydrocoupling of dinitrodiene 16 and (b) hydrodimerization of 1-nitrocyclohexene (17). Possible stereoisomers and their mirror images for the hydrodimers 2 and 18–23; R and S are the

Advances in the synthesis of functionalised pyrrolotetrathiafulvalenes

• Luke J. O’Driscoll,
• Sissel S. Andersen,
• Marta V. Solano,
• Dan Bendixen,
• Morten Jensen,
• Troels Duedal,
• Jess Lycoops,
• Cornelia van der Pol,
• Rebecca E. Sørensen,
• Karina R. Larsen,
• Kenneth Myntman,
• Christian Henriksen,
• Stinne W. Hansen and
• Jan O. Jeppesen

Beilstein J. Org. Chem. 2015, 11, 1112–1122, doi:10.3762/bjoc.11.125

• complication encountered with such functionalised TTFs is the existence of cis and trans stereoisomers. The investigation of the properties of a single isomer is challenging, not only due to difficulties in the separation of the isomers, but also because it is possible for the isomers to interconvert in the

Synthesis of novel N-cyclopentenyl-lactams using the Aubé reaction

• Madhuri V. Shinde,
• Rohini S. Ople,
• Ekta Sangtani,
• Rajesh Gonnade and
• D. Srinivasa Reddy

Beilstein J. Org. Chem. 2015, 11, 1060–1067, doi:10.3762/bjoc.11.119

• Carell et al. in 2007 [40]. The work of Aubé on AAC (azide–alkyne cycloaddition) chemistry also gives a good indication that equilibrating allylic azide stereoisomers can selectively participate in reactions [37][38][39][40][41][42][43][44][45]. In 2000, Aubé et al. proposed a mechanism for the

Discrete multiporphyrin pseudorotaxane assemblies from di- and tetravalent porphyrin building blocks

• Mirko Lohse,
• Larissa K. S. von Krbek,
• Sebastian Radunz,
• Suresh Moorthy,
• Christoph A. Schalley and
• Stefan Hecht

Beilstein J. Org. Chem. 2015, 11, 748–762, doi:10.3762/bjoc.11.85

• ethers on its corresponding axle are possible. One can therefore expect a mixture of stereoisomers to form. In the simplest case, A2@C2, two enantiomers and one meso-form are expected to exist, which should result in two overlapping sets of signals. For the other three complexes, the situation is even

• . The formation of unspecific complexes as well as fragmentation upon ionization have been found to be quite limited so that the picture obtained from the mass spectra can be expected to provide realistic insights into the composition of the complexes present in solution. As all stereoisomers have the

• broaden significantly, which is in agreement with the assumption that upon complexation the number of signals increases because the methylene protons become diasterotopic and different supramolecular stereoisomers can form. However, based on the present NMR spectroscopy data (Figure 7 and Figure 8) one

Synthesis of carbohydrate-scaffolded thymine glycoconjugates to organize multivalency

• Anna K. Ciuk and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2015, 11, 668–674, doi:10.3762/bjoc.11.75

• products (cf. Supporting Information File 1). Both regioisomers can consist of four different stereoisomers, two cis and two trans isomers according to the relative steric orientation of the thymine methyl groups. It can be assumed that the irradiation of 7 in diluted solution favors the syn

Novel stereocontrolled syntheses of tashiromine and epitashiromine

• Loránd Kiss,
• Enikő Forró and
• Ferenc Fülöp

Beilstein J. Org. Chem. 2015, 11, 596–603, doi:10.3762/bjoc.11.66

• stereoisomers (determined on the basis of 1H NMR data) failed, but the mixture could be applied in the next ring-opening oxidation step, since it gave only one open-chain diformyl intermediate I2. Similarly to the cis isomer, this unstable dialdehyde intermediate was subjected without isolation to catalytic

Enhancing the reactivity of 1,2-diphospholes in cycloaddition reactions

• Almaz Zagidullin,
• Vasili Miluykov,
• Elena Oshchepkova,
• Artem Tufatullin,
• Olga Kataeva and
• Oleg Sinyashin

Beilstein J. Org. Chem. 2015, 11, 169–173, doi:10.3762/bjoc.11.17

• would be assumed that similar [4 + 2] cycloadducts are formed according to the range of signals in the 31P NMR spectra. However, in this case, several stereoisomers are formed due to the high reactivity of the 1,2-diphospholes containing EWGs on the phosphorus atom. It should be noted that this is the

First chemoenzymatic stereodivergent synthesis of both enantiomers of promethazine and ethopropazine

• Paweł Borowiecki,
• Daniel Paprocki and
• Maciej Dranka

Beilstein J. Org. Chem. 2014, 10, 3038–3055, doi:10.3762/bjoc.10.322

• derivatives by means of PBr3, and subsequently reacted with appropriate amine providing desired pharmacologically valuable (R)- and (S)-stereoisomers of title drugs in an ee range of 84–98%, respectively. The modular amination procedure is based on a solvent-dependent stereodivergent transformation of the

• profiles of its stereoisomers, obtaining both enantiomers in more than analytical quantities is particularly desirable. Moreover, the racemic mixture of this pharmaceutical is commercially available, however it is sold at high price, as its production by standard synthetic procedures is time-consuming and

(2R,1'S,2'R)- and (2S,1'S,2'R)-3-[2-Mono(di,tri)fluoromethylcyclopropyl]alanines and their incorporation into hormaomycin analogues

• Armin de Meijere,
• Sergei I. Kozhushkov,
• Dmitrii S. Yufit,
• Christian Grosse,
• Marcel Kaiser and
• Vitaly A. Raev

Beilstein J. Org. Chem. 2014, 10, 2844–2857, doi:10.3762/bjoc.10.302

• with alkyl halides virtually yield single stereoisomers, in which the configuration of the newly formed stereogenic center at C-2 of the amino acid moiety is the same as that in the proline moiety of the chiral auxiliary in the starting material. In reactions of the enolate of this chiral glycine

• triflates of threonine stereoisomers [47], the chiral auxiliary approach [48][49][50][51] and enantioselective hydrogenation over a chiral catalyst [52][53]. All these approaches ought to be applicable to prepare unsubstituted β-methylphenylalanine, but most if not all of them have severe drawbacks. Among

• the chiral auxiliary approaches to β-branched arylalanines, including all four stereoisomers of β-methylphenylalanine, the one employing the "Evans amide" method with a 4-benzyl- or 4-phenyl-2-oxazolidinone moiety, has been used most frequently. Along this route, which requires eight procedural steps

Preparation of neuroprotective condensed 1,4-benzoxazepines by regio- and diastereoselective domino Knoevenagel–[1,5]-hydride shift cyclization reaction

• László Tóth,
• Yan Fu,
• Hai Yan Zhang,
• Attila Mándi,
• Katalin E. Kövér,
• Tünde-Zita Illyés,
• Attila Kiss-Szikszai,
• Balázs Balogh,
• Tibor Kurtán,
• Sándor Antus and
• Péter Mátyus

Beilstein J. Org. Chem. 2014, 10, 2594–2602, doi:10.3762/bjoc.10.272

• ). TDDFT-ECD calculation was proved an efficient method to determine the absolute configuration of separated stereoisomers of bioactive synthetic [19] and natural derivatives [20][21] on the basis of their HPLC-ECD spectra. For the configurational assignment of the separated enantiomers, TDDFT-ECD

Phosphinocyclodextrins as confining units for catalytic metal centres. Applications to carbon–carbon bond forming reactions

• Matthieu Jouffroy,
• Rafael Gramage-Doria,
• David Sémeril,
• Dominique Armspach,
• Dominique Matt,
• Werner Oberhauser and
• Loïc Toupet

Beilstein J. Org. Chem. 2014, 10, 2388–2405, doi:10.3762/bjoc.10.249

• trans (strong CO IR band at 1985 cm−1 [55][56]) configured. Remarkably, the same ratio of stereoisomers was obtained when rhodium complex 13 (see Scheme 6) was treated with LiCl under CO (1 atm). When the reaction between HUGPHOS-2 and [RhCl(CO)2]2 was repeated, but applying a 1:1 instead of 1:0.5

N–O Cleavage reactions of heterobicycloalkene-fused 2-isoxazolines

• Jaipal R. Nagireddy,
• Geoffrey K. Tranmer,
• Emily Carlson and
• William Tam

Beilstein J. Org. Chem. 2014, 10, 2200–2205, doi:10.3762/bjoc.10.227

• cleavage of carbobicycle-fused 2-isoxazolines converts both exo- and endo stereoisomers of 8 into the corresponding single isomer of cyclopentene 9 (Table 1) [20]. Since then, we have been interested in the outcomes of cleavage reactions of 2-isoxazolines fused to heterobicyclic compounds 10 or 11, which

Building complex carbon skeletons with ethynyl[2.2]paracyclophanes

• Ina Dix,
• Lidija Bondarenko,
• Peter G. Jones,
• Thomas Oeser and
• Henning Hopf

Beilstein J. Org. Chem. 2014, 10, 2013–2020, doi:10.3762/bjoc.10.209

• diastereomers are generated (as expected) by the oxidative dimerization of the mono ethynyl derivative [9], but assignment of the various spectra to specific stereoisomers remains an open question, and will only be possible after the resolution of the 4-ethynyl[2.2]paracyclophane, determination of its absolute

Synthesis of rigid p-terphenyl-linked carbohydrate mimetics

• Maja Kandziora and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 1749–1758, doi:10.3762/bjoc.10.182

• dioxolane C-2 (ratios close to 1:1). The preparation of syn-1,2-oxazine 4 was achieved in good yields ranging from 67–77% by stereocontrolled addition of lithiated (trimethylsilyl)ethoxyallene 9 to (Z)-nitrone 6 at −78 °C (Scheme 3). Although the formation of four stereoisomers is possible only two were

Multicomponent reactions in nucleoside chemistry

• Mariola Koszytkowska-Stawińska and
• Włodzimierz Buchowicz

Beilstein J. Org. Chem. 2014, 10, 1706–1732, doi:10.3762/bjoc.10.179

• , the uridine example is shown) [114]. The coupling products 98 were obtained as (Z)-stereoisomers for studies related to the drug discovery against the hepatitis C virus. The methodology shown in Scheme 40 [114] was further elaborated on reactions of polyfunctional iodide 99 with four equivalents of

cis–trans Isomerization of silybins A and B

• Michaela Novotná,
• Radek Gažák,
• David Biedermann,
• Florent Di Meo,
• Petr Marhol,
• Marek Kuzma,
• Lucie Bednárová,
• Kateřina Fuksová,
• Patrick Trouillas and
• Vladimír Křen

Beilstein J. Org. Chem. 2014, 10, 1047–1063, doi:10.3762/bjoc.10.105

• ; 10,11-cis-silybin; isomerization; silibinin; silybin; silymarin; Introduction The flavonolignan silybin (alternative name silibinin), occurring in the fruits of Silybum marianum (milk thistle), consists of two stereoisomers – silybin A (1a) and B (1b) – in a ca. 1:1 ratio (Figure 1). Their absolute

• (or 10 from 1b) on silica gel was not feasible, analogous to the preparative separation of silybin stereoisomers 1a and 1b (Figure 1), which was a challenge for several decades. It was accomplished as the separation of the respective silybin glycosides for the first time [13][14], later by HPLC [3

• -glucopyranoside 6''-gallate, Figure 6) was subjected to both, basic and acidic hydrolysis during its structure elucidation. However, under these conditions four stereoisomers of the original aglycon (2R,3R)-taxifolin were formed. Base-catalyzed isomerization of another taxifolin glycoside, (2R,3R)-2,3

Structure elucidation of female-specific volatiles released by the parasitoid wasp Trichogramma turkestanica (Hymenoptera: Trichogrammatidae)

• Armin Tröger,
• Teris A. van Beek,
• Martinus E. Huigens,
• Isabel M. M. S. Silva,
• Maarten A. Posthumus and
• Wittko Francke

Beilstein J. Org. Chem. 2014, 10, 767–773, doi:10.3762/bjoc.10.72

• an initial approach we aimed at the synthesis of a library of stereoisomers of A (Figure 2). The commercially available racemic anti-dimethyl 2,4-dimethylglutarate (1) was reduced to the corresponding racemate of 2,4-dimethylpentan-1,5-diol (2) [13], which was further transformed to the monosilyl

• position 2 underwent ca. 6% epimerization to yield 7 as a mixture of 4 stereoisomers. The synthesis of 2,6,8,12-tetramethyltrideca-2,4-diene (8) was completed by Wittig reaction using (3-methylbut-2-en-1-yl)triphenylphosphonium bromide [15]. As expected, the obtained mixture of all possible stereoisomers

• with malonate and another methylmalonate (including deoxygenation steps) seemed to be plausible [16]. These biogenetic considerations excluded methyl groups at positions 9 and 11. To prepare a mixture of all stereoisomers of 14, we again used 2 as the starting material (Figure 2). Monobenzylation to 9

Group-assisted purification (GAP) chemistry for the synthesis of Velcade via asymmetric borylation of N-phosphinylimines

• Jian-bo Xie,
• Jian Luo,
• Timothy R. Winn,
• David B. Cordes and
• Guigen Li

Beilstein J. Org. Chem. 2014, 10, 746–751, doi:10.3762/bjoc.10.69

• by avoiding traditional purification methods such as chromatography or recrystallization. The pure products, often pure stereoisomers, can be easily obtained by washing the crude products with common solvents or co-solvents [22][23][24][25]. Our GAP concept was attributed to the study of a series of

Synthesis of fluorescent (benzyloxycarbonylamino)(aryl)methylphosphonates

• Michał Górny vel Górniak,
• Anna Czernicka,
• Piotr Młynarz,
• Waldemar Balcerzak and
• Paweł Kafarski

Beilstein J. Org. Chem. 2014, 10, 741–745, doi:10.3762/bjoc.10.68

• chromatography, a significant enrichment in one of the diastereomers had been observed. For example, compound 7b obtained as a 55:45 molar mixture of stereoisomers after purification by means of chromatography was obtained as 85:15 molar mixture. The approach to obtain mixed esters bearing two aromatic moieties