Diels–Alder reactions in confined spaces: the influence of catalyst structure and the nature of active sites for the retro-Diels–Alder reaction

• Ángel Cantín,
• M. Victoria Gomez and
• Antonio de la Hoz

Beilstein J. Org. Chem. 2016, 12, 2181–2188, doi:10.3762/bjoc.12.208

• ] in where different stereoisomers could be obtained. Lewis-acid centers contained within the framework of zeolite beta (Zr-β, Sn-β) are useful catalysts in the Diels–Alder reaction for the production of bio-based terephthalic acid precursors, one of the monomers for the synthesis of polyethylene

Biosynthesis of oxygen and nitrogen-containing heterocycles in polyketides

• Franziska Hemmerling and
• Frank Hahn

Beilstein J. Org. Chem. 2016, 12, 1512–1550, doi:10.3762/bjoc.12.148

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• stabilize the carbanion intermediate, also increases the stereocenter’s susceptibility to racemization under the reaction conditions. Moreover, enolate intermediates can adopt E- or Z-geometries that, upon protonation, generally lead to opposite stereoisomers. Because enantioselective protonation is a

Modular synthesis of the pyrimidine core of the manzacidins by divergent Tsuji–Trost coupling

• Sebastian Bretzke,
• Stephan Scheeff,
• Felicitas Vollmeyer,
• Friederike Eberhagen,
• Frank Rominger and
• Dirk Menche

Beilstein J. Org. Chem. 2016, 12, 1111–1121, doi:10.3762/bjoc.12.107

• addition in more general terms and analyzed the addition reactions of allylmagnesium bromide both to 29 and 30. Notably, this route would allow to access all possible stereoisomers of the manzacidins, in agreement with the stereochemical diversity of this class of natural products. In detail, the synthesis

• urea-type cyclization precursor 19. Stereodivergent synthesis of 1,3-syn- and anti-tetrahydropyrimidinones [31]. Stereoselective synthesis of all possible stereoisomers of the manzacidin core amine by asymmetric addition to chiral tert-butanesulfinyl ketimines. Synthesis of the authentic cyclization

Efficient syntheses of climate relevant isoprene nitrates and (1R,5S)-(−)-myrtenol nitrate

• Sean P. Bew,
• Glyn D. Hiatt-Gipson,
• Graham P. Mills and
• Claire E. Reeves

Beilstein J. Org. Chem. 2016, 12, 1081–1095, doi:10.3762/bjoc.12.103

• ]. Evidently, to comprehensively investigate the role of individual IPNs within climate chemistry it is important that any synthetic protocol employed to generate IPNs affords either individual C=C stereoisomers or generates readily separable stereoisomers of the IPNs. Thus although the lack of synthetic

• purification afforded stereoisomers (E)-58 and (Z)-59 in a 2:1 ratio, respectively, and combined, unoptimized, 71% yield. Separation of the stereoisomers via flash column chromatography was straightforward. Pure (E)-58 and (Z)-59 were afforded with physicochemical properties essentially identical to those

Marine-derived myxobacteria of the suborder Nannocystineae: An underexplored source of structurally intriguing and biologically active metabolites

• Antonio Dávila-Céspedes,
• Peter Hufendiek,
• Max Crüsemann,
• Till F. Schäberle and
• Gabriele M. König

Beilstein J. Org. Chem. 2016, 12, 969–984, doi:10.3762/bjoc.12.96

• haliangicin stereoisomers, which differed in the configuration of the three terminal double bonds in the tetraene moiety. Each of the isomers haliangicin, haliangicin B, haliangicin C and haliangicin D happened to be present with two different configurations around the epoxy group. The NOESY spectra showed

Recent advances in N-heterocyclic carbene (NHC)-catalysed benzoin reactions

• Rajeev S. Menon,
• Akkattu T. Biju and
• Vijay Nair

Beilstein J. Org. Chem. 2016, 12, 444–461, doi:10.3762/bjoc.12.47

• - and galacto-configured dialdehydes 66 were promoted by the triazolium carbene precatalyst 22 to produce single inosose stereoisomers 67 in high yields (Scheme 40) [57]. Stereospecific reduction and deprotection of the inosose derivatives furnished allo- and epi-inositol in good yields. The camphor

Aluminacyclopentanes in the synthesis of 3-substituted phospholanes and α,ω-bisphospholanes

• Vladimir A. D’yakonov,
• Alevtina L. Makhamatkhanova,
• Rina A. Agliullina,
• Leisan K. Dilmukhametova,
• Tat’yana V. Tyumkina and
• Usein M. Dzhemilev

Beilstein J. Org. Chem. 2016, 12, 406–412, doi:10.3762/bjoc.12.43

• BuPCl2, the reaction with 3-benzyl-1-ethylaluminacyclopentane 1f affords the corresponding phospholanes 2g,h with one of the isomers predominating (Table 1). In the case of 3-cyclohexyl- and 3-(сyclohex-3-en-1-yl)-1-phenylphospholanes (2d and 2e), the number of stereoisomers increases owing to the

• /methanol = 5:3:1) and characterized in a separate fraction (Scheme 4). It should be noted that the phosphorus signals of major intensity of 2-aryl phospholane oxides 8a, 8b, 8d, 8e, 8f, corresponding to one of the stereoisomers, are shifted upfield by ca. 5–7 ppm with respect to those of 3-aryl-substituted

• the proximate asymmetric centres at C-3 and С-3′. Ratios of stereoisomers were determined by HPLC method as 2:1 (see Supporting Information File 2, Figure S1). Organophosphorus compounds, including cyclic ones, are known to readily form complexes with transition metals, which are extensively studied

Diastereoselective synthesis of new O-alkylated and C-branched inositols and their corresponding fluoro analogues

• Charlotte Collet,
• Françoise Chrétien,
• Yves Chapleur and
• Sandrine Lamandé-Langle

Beilstein J. Org. Chem. 2016, 12, 353–361, doi:10.3762/bjoc.12.39

• ; Introduction Inositol is a trivial name used to describe cyclohexanehexol compounds. Nine stereoisomers exist differing in the relative orientation of the hydroxy groups, the most naturally abounding and biologically important is myo-inositol [1][2]. The chemistry of inositols has been the theme of several

Interactions of cyclodextrins and their derivatives with toxic organophosphorus compounds

• Sophie Letort,
• Sébastien Balieu,
• William Erb,
• Géraldine Gouhier and
• François Estour

Beilstein J. Org. Chem. 2016, 12, 204–228, doi:10.3762/bjoc.12.23

• organophosphates is to be considered important insofar as the individual stereoisomers of a neurotoxic agent do not share the same level of toxicity [20]. Sarin (compounds 14a and 14b, Figure 5), cyclosarin (compounds 15a and 15b, Figure 5) and tabun (compounds 16a and 16b, Figure 5) consist of a mixture of two

• enantiomers. Due to the presence of two chiral centers (the phosphorus atom and the carbon atom of the 1,2,2-trimethylpropyloxy group), soman presents four stereoisomers: C(S)P(S), C(R)P(S), C(S)P(R) and C(R)P(R) (compounds 17a–d, Figure 5). CDs can tune a reaction mechanism in two ways: (a) by creating a

• agent stereoisomers’ absolute configuration of the phosphorus atom was not firmly established. Thus, the van Hooidonk and Breebaart’s work dating from 1970, it is highly probable that they did not attributed the correct absolute configurations to the enantiomers of sarin, which means that the (S

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