Tanzawaic acids I–L: Four new polyketides from Penicillium sp. IBWF104-06

• Louis P. Sandjo,
• Eckhard Thines,
• Till Opatz and
• Anja Schüffler

Beilstein J. Org. Chem. 2014, 10, 251–258, doi:10.3762/bjoc.10.20

• -dienoic acid unit was connected to the carbon at δC 79.0 (C-6). The relative configuration of the stereogenic centers was assigned based on NOESY data (Figure 1) and the previous work reported by Malmstrøm et al. on the stereochemistry of two related compounds, tanzawaic acids E and F [2]. The NOESY

• ). As in compounds 1–3, resonances of a (2E,4E)-penta-2,4-dienoic acid moiety as well as three additional CH groups, two CH2 groups and one CH3 for the completion of the decalin part were observed. The relative configuration of the stereogenic centers was determined by NOESY (Figure 4). Correlations

Boron-substituted 1,3-dienes and heterodienes as key elements in multicomponent processes

• Ludovic Eberlin,
• Fabien Tripoteau,
• François Carreaux,
• Andrew Whiting and
• Bertrand Carboni

Beilstein J. Org. Chem. 2014, 10, 237–250, doi:10.3762/bjoc.10.19

• three-component process (Scheme 3) [34]. Extension of this work to the intramolecular version is depicted in Scheme 4. The bicyclic lactone 1 was obtained stereoselectively from a diene-yne in a one-pot process with control of the relative stereochemistry of the five stereogenic centers [35]. Concerning

• boronated dienes 6, which were not isolated, but directly used in a one-pot Diels–Alder reaction/allylboration sequence. This efficiently generated, in high yields, tricyclic structures 7 with control of four stereogenic centers created (Scheme 8). In the presence of Grubbs II catalyst, a skeletal isomer 8

• with maleimides, as electron-poor dienophiles, followed by an allylboration (Scheme 21) [69]. This sequence proceeded with high stereocontrol, as already observed with the carbon and oxygen analogues. In addition, the absolute stereochemistry of the four new created stereogenic centers was controlled

Synthesis of new enantiopure poly(hydroxy)aminooxepanes as building blocks for multivalent carbohydrate mimetics

• Léa Bouché,
• Maja Kandziora and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2014, 10, 213–223, doi:10.3762/bjoc.10.17

• stereogenic center at the β-carbon (1,3-induction) has no or negligible influence. A few syn-selective additions of other nucleophiles to nitrones with two stereogenic centers similar to 6 or 8 were reported in the literature [38][39]. A preferred transition structure as depicted in Figure 1 plausibly

Synthesis of the B-seco limonoid core scaffold

• Hanna Bruss,
• Hannah Schuster,
• Rémi Martinez,
• Markus Kaiser,
• Andrey P. Antonchick and
• Herbert Waldmann

Beilstein J. Org. Chem. 2014, 10, 194–208, doi:10.3762/bjoc.10.15

• the thermodynamic enolate of 2-methylcyclohexanone (5) and the bicyclic electrophile 12 (Scheme 2). A challenging synthetic problem appears to be the construction of the stereochemically dense trans-fused C–D ring system 12, which possesses four stereogenic centers including two contiguous asymmetric

Studies on the interaction of isocyanides with imines: reaction scope and mechanistic variations

• Ouldouz Ghashghaei,
• Consiglia Annamaria Manna,
• Esther Vicente-García,
• Marc Revés and
• Rodolfo Lavilla

Beilstein J. Org. Chem. 2014, 10, 12–17, doi:10.3762/bjoc.10.3

• constitution of the azetidine 3a by spectroscopic methods (NMR, MS), the stereochemistry of the C=N bonds present in the structure remained unsolved. Furthermore, no conclusive nOe’s were observed to assign these stereogenic centers, and there were no reports in the literature regarding this point. A

Stereodivergent synthesis of jaspine B and its isomers using a carbohydrate-derived alkoxyallene as C₃-building block

• Volker M. Schmiedel,
• Stefano Stefani and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2013, 9, 2564–2569, doi:10.3762/bjoc.9.291

• sp. by Higa et al. [1]. In 2003 Debitus et al. were able to extract this natural product from the marine sponge Jaspis sp. [2]. Jaspine B (1) comprises a densely functionalized tetrahydrofuran ring, bearing three contiguous (2S,3S,4S)-configured stereogenic centers with a long alkyl chain at C-2 and

Gold(I)-catalyzed enantioselective cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2013, 9, 2250–2264, doi:10.3762/bjoc.9.264

• ], allowing the construction of six-membered adducts with up to three new stereogenic centers with complete diastereoselectivity and enantioselectivities of up to 91% ee (R1, R2 = Me, R4 = Ph, Scheme 11). With regard to the mechanism, it has been proposed that the activation of the allenamide by the gold

The chemistry of isoindole natural products

• Klaus Speck and
• Thomas Magauer

Beilstein J. Org. Chem. 2013, 9, 2048–2078, doi:10.3762/bjoc.9.243

• architecture and was first isolated from the fungus Aspergillus awamori in 2002 [74]. The highly functionalized pentacyclic skeleton comprises a unique 12-oxatricyclo[6.3.1.02,7]dodecane ring system and ten stereogenic centers. Its carbon framework is closely related to other members of the aspochalasin

Organocatalyzed enantioselective desymmetrization of aziridines and epoxides

• Ping-An Wang

Beilstein J. Org. Chem. 2013, 9, 1677–1695, doi:10.3762/bjoc.9.192

• [10][11][12] or epoxides [13][14][15] provides facile access to various chiral amines and alcohols and their derivatives with two adjacent stereogenic centers, which are widely used as building blocks in pharmaceutical and organic synthesis. The enantioselective catalytic desymmetrization of meso

Organocatalytic asymmetric selenofunctionalization of tryptamine for the synthesis of hexahydropyrrolo[2,3-b]indole derivatives

• Qiang Wei,
• Ya-Yi Wang,
• Yu-Liu Du and
• Liu-Zhu Gong

Beilstein J. Org. Chem. 2013, 9, 1559–1564, doi:10.3762/bjoc.9.177

• methanol, the optical purity of some products, such as 4e, was enhanced to >99% ee. Importantly, the configuration could be assigned by X-ray crystallography. The crystal structure of 4a (>99%) indicated that the configuration of the stereogenic centers was assigned to be (3aR,8aS) (Figure 3) [35]. On the

Catalytic asymmetric tandem Friedel–Crafts alkylation/Michael addition reaction for the synthesis of highly functionalized chromans

• Jiahuan Peng and
• Da-Ming Du

Beilstein J. Org. Chem. 2013, 9, 1210–1216, doi:10.3762/bjoc.9.137

• reaction; Introduction The development of efficient and convenient methods to access complex compounds with multiple stereogenic centers is one of the significant challenges in organic chemistry. Catalytic asymmetric tandem or cascade reactions are powerful tools to afford complex molecules with multiple

• stereogenic centers [1][2][3][4][5][6][7][8][9][10][11][12][13]. Newly developed tandem/domino reactions are increasingly applied in the synthesis of natural products and other biologically active compounds [14][15][16]. Dihydrocoumarins, chromans, and chromenes can be found in many natural products and

Inter- and intramolecular enantioselective carbolithiation reactions

• Asier Gómez-SanJuan,
• Nuria Sotomayor and
• Esther Lete

Beilstein J. Org. Chem. 2013, 9, 313–322, doi:10.3762/bjoc.9.36

• molecule by trapping the reactive organolithium intermediates with electrophiles. Several reviews have covered the synthetic applications of this kind of reaction [1][2][3][4][5][6][7][8]. When alkenes are used, up to two contiguous stereogenic centers may be generated, which may be controlled by using

One-pot tandem cyclization of enantiopure asymmetric cis-2,5-disubstituted pyrrolidines: Facile access to chiral 10-heteroazatriquinanes

• Ping-An Wang,
• Sheng-Yong Zhang and
• Henri B. Kagan

Beilstein J. Org. Chem. 2013, 9, 265–269, doi:10.3762/bjoc.9.32

• established that the reduction product 5a (Figure 3) was formed with a rigid 10-heteroazaquinane skeleton through an intramolecular Lewis acid–base pair interaction [15][16][17][18]. Three five-membered rings are fused to give a very stable bowl-shaped tricyclic system with five stereogenic centers

• , especially for one chiral nitrogen center and one chiral boron center. The configurations of the stereogenic centers in 5a are deduced from the configuration of the chiral auxiliary (S)-(−)-1-phenylethylamine to be S, 3S, 6R, 9S (chiral B atom) and 10R (chiral N atom), respectively. This novel tandem

• CH2Cl2, suitable for X-ray diffraction analysis. It was found that the ring-closing reaction took place during the heating process following N-methylation to provide the rigid 1-oxo-3-aza-10-azaquinane skeleton 7b as its ammonium salt. Compound 7b contains four stereogenic centers, and their

Organocatalytic tandem Michael addition reactions: A powerful access to the enantioselective synthesis of functionalized chromenes, thiochromenes and 1,2-dihydroquinolines

• Chittaranjan Bhanja,
• Satyaban Jena,
• Sabita Nayak and
• Seetaram Mohapatra

Beilstein J. Org. Chem. 2012, 8, 1668–1694, doi:10.3762/bjoc.8.191

• for constructing highly functionalized and enantiomerically enriched tetrahydro-6H-benzo[c]chromenes with five stereogenic centers. The reaction involved a domino oxa-Michael–Michael–Michael–aldol condensation of o-hydroxy-β-nitrostyrene 15 and two equivalents of α,β-unsaturated aldehydes in the

• -unsaturated nitro compounds 27 in toluene afforded chiral thiochromans 51 bearing three continuous stereogenic centers with high diastereo- and enantioselectivities by this novel cascade process (Scheme 26). 3. Organocatalytic aza-Michael reactions to access functionalized 1,2-dihydroquinolines 3.1. Reaction

Synthesis of chiral sulfoximine-based thioureas and their application in asymmetric organocatalysis

• Marcus Frings,
• Isabelle Thomé and
• Carsten Bolm

Beilstein J. Org. Chem. 2012, 8, 1443–1451, doi:10.3762/bjoc.8.164

• additional stereogenic centers, alternative molecules with substituted ethylene linkers ((SS,SC)-18 and (RS,SC)-19) were designed. Their syntheses are outlined in Scheme 5, which also underlines the value of the highly modular preparative approach towards such compounds leading to a variety of molecules by

• ) provided (homochiral) (SS,SC)-14 in good yield (74%). Already at this early stage we wondered, which of the two stereogenic centers in the resulting thioureas – the one at the sulfur atom or the one stemming from the amino acid – would determine the absolute configuration of the catalysis products. For

• leading to higher enantioselectivities. Perhaps, substituted arene backbones could be used for inducing enhanced positive effects on both units through electronic fine-tuning. The additional stereogenic centers in the ethylene linker as in (SS,SC)-18 and (RS,SC)-19 had none or at best only a minor impact

Organocatalytic asymmetric Michael addition of unprotected 3-substituted oxindoles to 1,4-naphthoquinone

• Jin-Sheng Yu,
• Feng Zhou,
• Yun-Lin Liu and
• Jian Zhou

Beilstein J. Org. Chem. 2012, 8, 1360–1365, doi:10.3762/bjoc.8.157

• ][10], 3-aminooxindoles [11][12][13][14][15] and 3-quaternary oxindoles [16][17][18][19][20]. Despite achievements, the catalytic asymmetric synthesis of 3,3-diaryloxindoles has not been reported. This is possibly due to the challenge in the construction of such congested quaternary stereogenic centers

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

• 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

• , iridoids are usually associated with defense chemistry. Whilst configurations at the stereogenic centers of 15 and related iridoid lactones in insects appear to be stereotypic, several monocyclic iridoids show further stereochemical variation. Lactol 16 and iridodial (17) have first been identified as

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

• 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

Enantioselective supramolecular devices in the gas phase. Resorcin[4]arene as a model system

• Caterina Fraschetti,
• Matthias C. Letzel,
• Antonello Filippi,
• Maurizio Speranza and
• Jochen Mattay

Beilstein J. Org. Chem. 2012, 8, 539–550, doi:10.3762/bjoc.8.62

• may exist in a highly symmetric bowl-shaped conformation, a so-called cone conformation, or in several other asymmetric conformations. In general, the chirality of resorcin[4]arenes can be due to (1) the presence of stereogenic centers in their side chains, or (2) the hindered spatial arrangement of

The interplay of configuration and conformation in helical perylenequinones: Insights from chirality induction in liquid crystals and calculations

• Elisa Frezza,
• Silvia Pieraccini,
• Stefania Mazzini,
• Alberta Ferrarini and
• Gian Piero Spada

Beilstein J. Org. Chem. 2012, 8, 155–163, doi:10.3762/bjoc.8.16

• the determination of the absolute configuration [2][3][5][6][12][13][14][15][16][17][18][19][20][21][22][23][24]. In fact, this technique has been fruitfully applied to different classes of systems, possessing either stereogenic centers or axial chirality. In this work, chirality induction in liquid

One-pot Diels–Alder cycloaddition/gold(I)-catalyzed 6-endo-dig cyclization for the synthesis of the complex bicyclo[3.3.1]alkenone framework

• Boubacar Sow,
• Gabriel Bellavance,
• Francis Barabé and
• Louis Barriault

Beilstein J. Org. Chem. 2011, 7, 1007–1013, doi:10.3762/bjoc.7.114

• ][27][28][29][30][31] to afford intermediate B, which after proto-deauration and hydrolysis affords the bridgehead ketone 15. The attractive feature of this process resides in the ability to generate four new stereogenic centers and three new C–C bonds in one single operation. To validate the above

A practical two-step procedure for the preparation of enantiopure pyridines: Multicomponent reactions of alkoxyallenes, nitriles and carboxylic acids followed by a cyclocondensation reaction

• Christian Eidamshaus,
• Roopender Kumar,
• Mrinal K. Bera and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2011, 7, 962–975, doi:10.3762/bjoc.7.108

• enantiopurity [40]. Chiral carboxylic acids are readily available and their use would allow for a rapid access to pyridines with side chains bearing stereogenic centers. In recent years we studied intensively the multicomponent reactions of lithiated alkoxyallenes with nitriles and carboxylic acids and could

• stereogenic centers in α-position, compounds 18, 22 and 40 were transformed into esters 50, 49 and 51, respectively (Table 2). Treatment of the pyridones with Mosher acid chloride in a mixture of pyridine and dichloromethane as solvent afforded the desired esters in good yields. Comparison with the

When gold can do what iodine cannot do: A critical comparison

• Sara Hummel and
• Stefan F. Kirsch

Beilstein J. Org. Chem. 2011, 7, 847–859, doi:10.3762/bjoc.7.97

• realizing a highly efficient domino reaction that creates two new stereogenic centers and three new bonds. Other heteroatoms have also been successfully employed as internal nucleophiles for the trapping of positive charges. In gold-catalyzed cyclizations, Kozmin and co-workers reported the

A comparative study of the Au-catalyzed cyclization of hydroxy-substituted allylic alcohols and ethers

• Berenger Biannic,
• Thomas Ghebreghiorgis and
• Aaron Aponick

Beilstein J. Org. Chem. 2011, 7, 802–807, doi:10.3762/bjoc.7.91

• biologically interesting and structurally complex natural products [1]. These compounds are typically densely functionalized and contain numerous stereogenic centers. Many challenges for the total synthesis of these molecules revolve around issues of selectivity and can be complicated by the presence of

Alkene selenenylation: A comprehensive analysis of relative reactivities, stereochemistry and asymmetric induction, and their comparisons with sulfenylation

• Vadim A. Soloshonok and
• Donna J. Nelson

Beilstein J. Org. Chem. 2011, 7, 744–758, doi:10.3762/bjoc.7.85

• alkenols 4 is reversed, because of the opposite stereochemistry of the chiral stereogenic centers in 1 versus 2. While not included in this study, it should be emphasized that analogous stereochemical outcomes were observed in the corresponding reactions of chiral electrophiles 1 and 2 with carboxylic