Topochemical control of the photodimerization of aromatic compounds by γ-cyclodextrin thioethers in aqueous solution

• Hai Ming Wang and
• Gerhard Wenz

Beilstein J. Org. Chem. 2013, 9, 1858–1866, doi:10.3762/bjoc.9.217

• the dominant factor, but rather the pre-organization of the guest molecules in the CD cavity prior to excitation has the greatest effect. The distribution of the stereoisomers appears to be mainly topochemically [5] controlled because of the short lifetime of the excited state of COU. Quantum

Self-assembly of 2,3-dihydroxycholestane steroids into supramolecular organogels as a soft template for the in-situ generation of silicate nanomaterials

• Valeria C. Edelsztein,
• Andrea S. Mac Cormack,
• Matías Ciarlantini and
• Pablo H. Di Chenna

Beilstein J. Org. Chem. 2013, 9, 1826–1836, doi:10.3762/bjoc.9.213

• key to the directed design of new organogels. We report herein the organogelating property of four stereoisomers of the simple steroid 2,3-dihydroxycholestane. Only the isomer with the trans-diaxial hydroxy groups had the ability to gelate a broad variety of liquids and, thus, to be a super

• the stereoisomers 2–4 bearing equatorial hydroxy groups (Figure 1). The gelation ability of 1 is discussed in terms of the Hansen solubility parameters and Kamlet–Taft parameters based on its behavior in a set of 33 solvents. We also report on the sol–gel polymerization of TEOS carried out with gels

• fibrillar network of the gel. Tubular nanostructured materials, such as these presented here, may offer alternatives over spherical nanoparticles for some biomedical and biotechnological applications [30][31]. Conclusion In summary, we have studied the organogelating behavior of the four stereoisomers of

α-Bromodiazoacetamides – a new class of diazo compounds for catalyst-free, ambient temperature intramolecular C–H insertion reactions

• Åsmund Kaupang and
• Tore Bonge-Hansen

Beilstein J. Org. Chem. 2013, 9, 1407–1413, doi:10.3762/bjoc.9.157

• exo-5a–f). The stereochemistry of the obtained β-lactams was determined based on the previously published NMR data for endo/exo-5b [45], as well as on the characteristic magnitude of the couplings and chemical shift values of the α-protons of the endo/exo stereoisomers [46][47][48][49]. The high

Efficient regio- and stereoselective access to novel fluorinated β-aminocyclohexanecarboxylates

• Loránd Kiss,
• Melinda Nonn,
• Reijo Sillanpää,
• Santos Fustero and
• Ferenc Fülöp

Beilstein J. Org. Chem. 2013, 9, 1164–1169, doi:10.3762/bjoc.9.130

• 9 in good yield (Scheme 2). The synthetic route presented above could be extended to the preparation of other 4-fluorinated cyclohexane amino acid derivatives, stereoisomers of 7 or 9. Ethyl trans-2-aminocyclohex-4-enecarboxylate 10 [57] was analogously transformed to its cis counterpart through

Study on the total synthesis of velbanamine: Chemoselective dioxygenation of alkenes with PIFA via a stop-and-flow strategy

• Huili Liu,
• Kuan Zheng,
• Xiang Lu,
• Xiaoxia Wang and
• Ran Hong

Beilstein J. Org. Chem. 2013, 9, 983–990, doi:10.3762/bjoc.9.113

• -exo-trig cyclization is the favorable pathway during the PIFA-mediated amide-cyclization of alkene. Two isomers after cyclization were then attributed to the stereoisomers of the C=N double bond in the iminolactone C. This notion is also consistent with numerous reports on the iodocyclization with

Highly stereocontrolled synthesis of trans-enediynes via carbocupration of fluoroalkylated diynes

• Tsutomu Konno,
• Misato Kishi and
• Takashi Ishihara

Beilstein J. Org. Chem. 2012, 8, 2207–2213, doi:10.3762/bjoc.8.249

• enediynes 14a–c in high to excellent yields. In all cases, other stereoisomers were not detected at all and 14a–c were generated as the sole products in a pure form. Conclusion In summary, we have established a convenient as well as efficient access to the trifluoromethylated diyne by Sonogashira cross

• . Finally, the thus-obtained iodide underwent a smooth Sonogashira cross-coupling reaction to afford the various desired trans-enediyne derivatives in high yields. trans-Enediyne. Regio- and stereoisomers. Synthetic strategy for the preparation of trifluoromethylated diynes. Preparation of various enynes. A

The multicomponent approach to N-methyl peptides: total synthesis of antibacterial (–)-viridic acid and analogues

• Ricardo A. W. Neves Filho,
• Sebastian Stark,
• Bernhard Westermann and
• Ludger A. Wessjohann

Beilstein J. Org. Chem. 2012, 8, 2085–2090, doi:10.3762/bjoc.8.234

• pursued. The advantages of the MCR protocol are speed, variability, insensitivity to steric crowding, safe peptoid-moiety formation, and access to equally distributed stereoisomers (which can be a disadvantage though, once the most active isomer is identified). The improved classical approach gave the

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

A new approach toward the total synthesis of (+)-batzellaside B

• Jolanta Wierzejska,
• Shin-ichi Motogoe,
• Yuto Makino,
• Tetsuya Sengoku,
• Masaki Takahashi and
• Hidemi Yoda

Beilstein J. Org. Chem. 2012, 8, 1831–1838, doi:10.3762/bjoc.8.210

• appealing performance observed in the above synthetic process, this reaction protocol has the major disadvantage of low stereoselectivity causing operational inconvenience associated with the laborious chromatographic separation of the two stereoisomers. From the practical considerations, we next explored a

Exploring chemical diversity via a modular reaction pairing strategy

• Joanna K. Loh,
• Sun Young Yoon,
• Thiwanka B. Samarakoon,
• Alan Rolfe,
• Patrick Porubsky,
• Benjamin Neuenswander,
• Gerald H. Lushington and
• Paul R. Hanson

Beilstein J. Org. Chem. 2012, 8, 1293–1302, doi:10.3762/bjoc.8.147

• on multigram scale through the use of three efficient steps, namely sulfonylation, Mitsunobu alkylation and SNAr, to generate both stereoisomers of each core [37] (Scheme 2). The bridged benzofused sultam scaffolds were prepared by a sulfonylation intramolecular SNAr protocol, reported previously [32

• composed of the entire spectrum of possible stereoisomers, and library II (5–8) was composed of two sets of benzofused sultams having an H or Me group at the R1 position. The use of all possible stereoisomers provides the opportunity to generate stereochemical SAR (SSAR) for each building block combination

On the proposed structures and stereocontrolled synthesis of the cephalosporolides

• Sami F. Tlais and
• Gregory B. Dudley

Beilstein J. Org. Chem. 2012, 8, 1287–1292, doi:10.3762/bjoc.8.146

• Sami F. Tlais Gregory B. Dudley Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390 USA, Fax: (850) 644-8281 10.3762/bjoc.8.146 Abstract The synthesis of four candidate stereoisomers of cephalosporolide H is described, made possible by a zinc-chelation

• correlation between bioactivity and spiroketal stereochemistry in many natural spiroketals. For example, cephalostatin and ritterazine feature thermodynamically disfavored spiroketals that are more cytotoxic than their stereoisomers [12]. Other prominent cytotoxic spiroketals include spongistatin [7] and

• population control) requires the ability to prepare specific spiroketal stereoisomers. Anomeric effects typically guide the stereochemical preferences in 6,6 and 5,6-spiroketals [7][17][18][19][20], whereas 5,5-spiroketal stereochemistry is more difficult to predict [21] and control [22][23][24][25]. This

The preferred conformation of erythro- and threo-1,2-difluorocyclododecanes

• Yi Wang,
• Peer Kirsch,
• Tomas Lebl,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2012, 8, 1271–1278, doi:10.3762/bjoc.8.143

• data to the Eyring equation [15] allowed determination of the activation parameters (see Table 1 and Supporting Information File 1). The overall free energy change (ΔG#) is similar in each case and both the erythro 5a and threo 5b stereoisomers have conformational energy barriers ~2–3 kcal·mol−1 higher

• erythro (5a) and threo (5b) stereoisomers of 1,2-difluorocyclododecane. Synthetic routes to erythro- (5a) and threo-1,2-difluorocyclododecane (5b). The activation parameters of erythro- (5a) and threo- (5b) 1,2-difluorocyclododecanes. The corner C–C–C angles for conformers VI and VII of the threo isomer

Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part II: Iridomyrmecins

• Robert Hilgraf,
• Nicole Zimmermann,
• Lutz Lehmann,
• Armin Tröger and
• Wittko Francke

Beilstein J. Org. Chem. 2012, 8, 1256–1264, doi:10.3762/bjoc.8.141

• , all eight stereoisomers of trans-fused iridomyrmecins were synthesized starting from the enantiomers of limonene. Combined gas chromatography and mass spectrometry including enantioselective gas chromatography revealed that volatiles released by the endohyperparasitoid wasp Alloxysta victrix contain

• targets in stereoselective synthesis. Similar to dihydronepetalactones, the iridomyrmecin skeleton shows four contiguous stereogenic centers giving rise to four trans-fused stereoisomers A–D and four corresponding enantiomers A'–D' (Figure 3, D' is identical to 2 in Figure 1). The presence of the four

• route may generally be used for the synthesis of all eight stereoisomers of trans-fused iridomyrmecins, it suffers from several major disadvantages such as high costs of (S)-pulegone and difficult separations of diastereomeric mixtures. Starting from the cheaply available pure enantiomers of limonene

Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part I: Dihydronepetalactones

• Nicole Zimmermann,
• Robert Hilgraf,
• Lutz Lehmann,
• Daniel Ibarra and
• Wittko Francke

Beilstein J. Org. Chem. 2012, 8, 1246–1255, doi:10.3762/bjoc.8.140

• Nicole Zimmermann Robert Hilgraf Lutz Lehmann Daniel Ibarra Wittko Francke Department of Chemistry - Organic Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany 10.3762/bjoc.8.140 Abstract Starting from the enantiomers of limonene, all eight stereoisomers of

• trans-fused dihydronepetalactones were synthesized. Key compounds were pure stereoisomers of 1-acetoxymethyl-2-methyl-5-(2-hydroxy-1-methylethyl)-1-cyclopentene. The stereogenic center of limonene was retained at position 4a of the target compounds and used to stereoselectively control the introduction

• stereogenic centers, giving rise to eight trans-fused stereoisomers a–d and the corresponding enantiomers a'–d' (Figure 3). Whilst several stereoselective syntheses of the relatively widespread and well known cis-fused nepetalactone and its dihydro derivatives have been carried out [16][17][18][19], only very

Synthesis of 2,6-disubstituted tetrahydroazulene derivatives

• Zakir Hussain,
• Henning Hopf,
• Khurshid Ayub and
• S. Holger Eichhorn

Beilstein J. Org. Chem. 2012, 8, 693–698, doi:10.3762/bjoc.8.77

• compound(s) was found to give a mixture of stereoisomers. However, in the present case, we were only able to isolate 4 as a single stereoisomer. Furthermore, the procedure for the synthesis of compounds 4 and 5 is essentially the same as described previously for analogous compounds [10]. The complete

An easy α-glycosylation methodology for the synthesis and stereochemistry of mycoplasma α-glycolipid antigens

• Yoshihiro Nishida,
• Yuko Shingu,
• Yuan Mengfei,
• Kazuo Fukuda,
• Hirofumi Dohi,
• Sachie Matsuda and
• Kazuhiro Matsuda

Beilstein J. Org. Chem. 2012, 8, 629–639, doi:10.3762/bjoc.8.70

• and characterized by other groups [11][12][13][14]. Absolute chemical structures of GGPL-I [15] and GGPL–III [16] have already been established by chemical syntheses of stereoisomers; these α-glycolipids have a common chemical backbone of 3-O-(α-D-glucopyranosyl)-sn-glycerol carrying phosphocholine at

Synthesis of fluorinated maltose derivatives for monitoring protein interaction by ¹⁹F NMR

• Michaela Braitsch,
• Hanspeter Kählig,
• Georg Kontaxis,
• Michael Fischer,
• Toshinari Kawada,
• Robert Konrat and
• Walther Schmid

Beilstein J. Org. Chem. 2012, 8, 448–455, doi:10.3762/bjoc.8.51

• fluorination with DAST [34][35] yielded a mixture of fluorinated disaccharides: The desired product 22 [39] was isolated by column chromatography and Zemplén deprotection yielded derivative 23. Binding studies using the 2-F-maltose reporter system The binding properties of the two stereoisomers of 2-19F

• -labeled maltose (gluco- and manno-type) to the maltose-binding protein and a MBP-V53 fusion protein comprising five V3 modules of the LDL receptor in a linear tandem arrangement (V33333) were analyzed. As can be seen in Figure 3 and Figure 4, the stereoisomers of 2-F labeled maltose clearly exhibit

Synthesis of fused tricyclic amines unsubstituted at the ring-junction positions by a cascade condensation, cyclization, cycloaddition then decarbonylation strategy

• Iain Coldham,
• Adam J. M. Burrell,
• Hélène D. S. Guerrand,
• Luke Watson,
• Nathaniel G. Martin and
• Niall Oram

Beilstein J. Org. Chem. 2012, 8, 107–111, doi:10.3762/bjoc.8.11

• alpha to the nitrogen atom (2.20 ppm, doublet, J = 11.5 Hz). However, this transformation was not entirely stereoselective and a (separable) mixture of two other stereoisomers 22 and 23 was also formed (NOESY studies were used to ascertain the relative stereochemistry). To complete the desired aim to

Synthesis of highly functionalized β-aminocyclopentanecarboxylate stereoisomers by reductive ring opening reaction of isoxazolines

• Melinda Nonn,
• Loránd Kiss,
• Reijo Sillanpää and
• Ferenc Fülöp

Beilstein J. Org. Chem. 2012, 8, 100–106, doi:10.3762/bjoc.8.10

• Peramivir analogues has recently been investigated as potential antiviral agents [46][47]. Results and Discussion We recently reported a regio- and stereoselective procedure for the formation of a series of isoxazoline-fused cispentacin and transpentacin regio- and stereoisomers (2–6) from bicyclic β-lactam

• 1 [48][49] (Scheme 1). The syntheses consisted of a dipolar cycloaddition of nitrile oxide (generated with Boc2O, Et3N and DMAP) to the olefinic bond of cis-ethyl 2-aminocyclopent-3-enecarboxylate derived from 1, during which the isoxazoline-fused amino ester regio- and stereoisomers (2 and 4) were

• are excellent precursors for the construction of different functional groups through reductive ring cleavage, our recent aim was to synthesize highly functionalized β-aminocyclopentanecarboxylate regio- and stereoisomers from the earlier prepared isoxazoline-fused cispentacin and transpentacin

Synthesis of 2-amino-3-arylpropan-1-ols and 1-(2,3-diaminopropyl)-1,2,3-triazoles and evaluation of their antimalarial activity

• Matthias D’hooghe,
• Stéphanie Vandekerckhove,
• Karen Mollet,
• Karel Vervisch,
• Stijn Dekeukeleire,
• Liesbeth Lehoucq,
• Carmen Lategan,
• Peter J. Smith,
• Kelly Chibale and
• Norbert De Kimpe

Beilstein J. Org. Chem. 2011, 7, 1745–1752, doi:10.3762/bjoc.7.205

• -chloroazetidin-2-ones as the major stereoisomers after condensation with chloroketene in benzene [30], racemic cis-3-chloro-β-lactams 10a,b were prepared and converted into cis-2-aryl-3-(hydroxymethyl)aziridines 11a,b upon treatment with two molar equiv of LiAlH4 in Et2O under reflux for 15 h (Scheme 2). Next

• SN2 fashion [30]. The formation of the other regio- and stereoisomers was excluded based on detailed spectroscopic analysis. It should be noted that both diastereomeric antipodes of the class of 1-aryl-2-aminopropan-1,3-diols, i.e., anti- and syn-aminopropanols 9 and 12, can now be prepared

Natural product biosyntheses in cyanobacteria: A treasure trove of unique enzymes

• Jan-Christoph Kehr,
• Douglas Gatte Picchi and
• Elke Dittmann

Beilstein J. Org. Chem. 2011, 7, 1622–1635, doi:10.3762/bjoc.7.191

• group resulting in either 7-epi-cylindrospermopsin or cylindrospermopsin. The proportion of these two epimers varies in different cylindrospermopsin producing strains. It remains to be shown if the corresponding hydroxylase produces both stereoisomers or if a second unidentified hydroxylase is involved

Dependency of the regio- and stereoselectivity of intramolecular, ring-closing glycosylations upon the ring size

• Patrick Claude,
• Christian Lehmann and
• Thomas Ziegler

Beilstein J. Org. Chem. 2011, 7, 1609–1619, doi:10.3762/bjoc.7.189

• size spacer n = 2 (constitutions 6d, 7d, 8d, and further the isomer β(1→2), were not observed). The various regio- and stereoisomers were modeled and subjected to molecular dynamics (MD) runs of at least 5000 ps, wherefrom the observed major diastereomer 8d emerged with a lowest free energy by more

• than 2.2 kcal/mol with respect to the β(1→3) isomer 6d. Most-stable product conformations for the cyclo-glycosidation reaction with ring size spacer n = 3 (constitutions 6c, 7c, 8c, and further the isomer β(1→2), were not observed). As in Figure 6, the various regio- and stereoisomers were modeled and

• cyclo-glycosidation reaction with ring size spacer n = 4 (constitutions 6b, 7b, 8b, and further the isomer β(1→2), were not observed). As in Figure 6, the various regio- and stereoisomers were modeled and subjected to molecular dynamics (MD) runs of at least 5000 ps, wherefrom the observed major

Functionalization of anthracene: A selective route to brominated 1,4-anthraquinones

• Kiymet Berkil Akar,
• Osman Cakmak,
• Orhan Büyükgüngör and
• Ertan Sahin

Beilstein J. Org. Chem. 2011, 7, 1036–1045, doi:10.3762/bjoc.7.118

• (Scheme 2). Although the methanolysis was repeated several times, the product ratio remained almost the same. The compounds were separable by column chromatography and were isolated in 29 and 44% yield for 7 and 8, respectively. There are three possible stereoisomers that can be formed in the reaction

• reaction of both the methoxy stereoisomers 7 and 8, generated from hexabromide 6, and of methoxy compound 12, obtained from hexabromide 2 and 3, gave the same compounds 10 and 11 by elimination of one mol of HBr and CH3OH. In conclusion, a convenient and effective procedure for the synthesis of dimethoxy 7

Multicomponent reaction access to complex quinolines via oxidation of the Povarov adducts

• Esther Vicente-García,
• Rosario Ramón,
• Sara Preciado and
• Rodolfo Lavilla

Beilstein J. Org. Chem. 2011, 7, 980–987, doi:10.3762/bjoc.7.110

• of stereoisomers [9][10][11][12][13]. Unfortunately, no general methods for enantioselective Povarov reactions have been developed (for examples of catalytic enantioselective transformations operating in particular systems, see [14][15]), and this constitutes a serious drawback in the use of this

Long-range diastereoselectivity in Ugi reactions of 2-substituted dihydrobenzoxazepines

• Luca Banfi,
• Andrea Basso,
• Valentina Cerulli,
• Valeria Rocca and
• Renata Riva

Beilstein J. Org. Chem. 2011, 7, 976–979, doi:10.3762/bjoc.7.109

• the isocyanide derived substituent prefers an axial position in both stereoisomers, as demonstrated by NOE experiments carried out on 6e (Supporting Information File 2). Thus, after attack, the trans initial adduct 10 undergoes a conformational change to 11. The two vicinal J2-3 (i.e., 2.1 and 9.3 Hz

• coupling constants for the two stereoisomers is not large enough to guarantee the undisputable assignment of the cis relative configuration to the major adduct. In the presented hypothesis, the function of the substituent at C-2 would therefore not be to shield one of the two diastereotopic faces, but only