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

Oxalyl retro-peptide gelators. Synthesis, gelation properties and stereochemical effects

• Janja Makarević,
• Milan Jokić,
• Leo Frkanec,
• Vesna Čaplar,
• Nataša Šijaković Vujičić and
• Mladen Žinić

Beilstein J. Org. Chem. 2010, 6, 945–959, doi:10.3762/bjoc.6.106

• arrangements of i-Bu groups occur (Figure 10b, Newman projections of two stereogenic centers only). Our earlier results based on single crystal X-ray analysis of bis(amino acid)oxalamides showed that their most stable conformations are characterized by vicinal positioning of the methine proton at the

• of (S,S)-1b (top) and (S,R)-1b generated by systematic conformational search (SYBYL package; second graphic); (b) Partial Newman projections of two stereogenic centers of (S,R)-1b and (S,S)-1b showing conformations with cis-arrangement of i-Bu groups in the former (A) and trans- (B, D) and cis- (C

• carboxylic acid, methyl ester and carboxamide, namely (S,S)-bis(LeuLeu) 1a, b, c; (S,S)-bis(PhgPhg) 3a, b, c and (S,S)-bis(PhePhe) 5a, b, c and, the second containing two different amino acids, (S,S)-bis(LeuPhg) 2a, b, c and (S,S)-bis(PhgLeu) 4a, b, c (configurations of only two of the four stereogenic

Novel tetracyclic structures from the synthesis of thiolactone-isatin hybrids

• Renate Hazel Hans,
• Hong Su and
• Kelly Chibale

Beilstein J. Org. Chem. 2010, 6, No. 78, doi:10.3762/bjoc.6.78

• carbon and nitrogen pyramidality (χC and χN) and the N-C(=O) and C=O bond lengths (Table 3) all indicate that the bridge amide bond is essentially relaxed. In summary we have described the straightforward synthesis of novel compounds 3 and 4. The latter bears quaternary stereogenic centers and a

Synthesis and binding studies of two new macrocyclic receptors for the stereoselective recognition of dipeptides

• Ana Maria Castilla,
• M. Morgan Conn and
• Pablo Ballester

Beilstein J. Org. Chem. 2010, 6, No. 5, doi:10.3762/bjoc.6.5

• sheet structure with an included peptide ligand. Conversely, the two outer strands of receptor 2 are oriented parallel to each other (“parallel receptor”), such that the covalent connections between strands join similar stereogenic centers, C-terminus with C-terminus and N-terminus with N-terminus

• . Receptor 2 is anticipated to form an antiparallel sheet structure with the included peptide ligand. This change in connectivity does not involve any inversion of the stereogenic centers but only a modification in the sequence of peptide-coupling reactions that yield the cyclic structure, and will be

• steric clashes between the methyl groups of the target peptide and the benzophenone linking chains, the stereogenic centers in the linkers must have the (S) configuration, opposite to that of the bound peptide (R); b) the benzophenone aromatic ring will also provide a hydrophobic pocket for the

The role of an aromatic group in remote chiral induction during conjugate addition of α-sulfonylallylic carbanions to ethyl crotonate

• Shlomo Levinger,
• Ranjeet Nair and
• Alfred Hassner

Beilstein J. Org. Chem. 2008, 4, No. 32, doi:10.3762/bjoc.4.32

• addition products resulting from the formation of two new stereogenic centers (methine carbon atoms 3 and 4 of the ethyl hexenoates, see Scheme 1) only two could be detected in all cases except the 9-anthryl derivative (3h), which indicated a single adduct. Apart from having proceeded regioselectively (α

• yields are obtained with aromatic rings possessing higher electron density (4-methoxyphenyl, 2-thienyl) while the employment of the 9-anthryl nucleus results in complete transmission of chirality to the newly formed stereogenic centers. Ab initio calculations assign an important role to Li+–aromatic π

Stereoselective synthesis of (2S,3S,4Z)-4-fluoro- 1,3-dihydroxy- 2-(octadecanoylamino)octadec- 4-ene, [(Z)-4-fluoroceramide], and its phase behavior at the air/water interface

• Gergana S. Nikolova and
• Günter Haufe

Beilstein J. Org. Chem. 2008, 4, No. 12, doi:10.3762/bjoc.4.12

• , the D-erythro-configuration of the stereogenic centers is most probable, considering the reaction mechanism we propose in Scheme 2. Moreover, the 3JH,H-coupling constants between the protons at C(2) and C(3), which were determined to be 7.8 Hz and 7.7 Hz for 5 and 6, respectively, support this

• diastereo- and enantioselective synthetic route was presented for the preparation of the first analogues 1b and 2b, fluorinated in 4-position, of the natural signaling molecules sphingosine (1a) and ceramide (2a) with the required D-erythro-configuration (2S,3S) of the stereogenic centers and a Z configured

An asymmetric synthesis of all stereoisomers of piclavines A1-4 using an iterative asymmetric dihydroxylation

• Yukako Saito,
• Naoki Okamoto and
• Hiroki Takahata

Beilstein J. Org. Chem. 2007, 3, No. 37, doi:10.1186/1860-5397-3-37

• sequence of iterative AD reactions starting from an achiral N-pentenylphthalimide (11). [9] The two stereogenic centers in 10 were constructed with high enantio-enhancement via a sequence of twofold AD reactions as shown in Scheme 2. We embarked on the synthesis of piclavines A1-4 using the four

Reagent controlled addition of chiral sulfur ylides to chiral aldehydes

• Varinder K. Aggarwal and
• Jie Bi

Beilstein J. Org. Chem. 2005, 1, No. 4, doi:10.1186/1860-5397-1-4

• of the two enantiomers of the chiral benzyl sulfonium salt 1 with glyceraldehyde acetonide were studied in detail. Of the two new stereogenic centers created, it was found that the C1 stereochemistry was largely controlled by the reagent, whereas control at the C2 center was dependent on the aldehyde

Mixtures of monodentate P-ligands as a means to control the diastereoselectivity in Rh-catalyzed hydrogenation of chiral alkenes

• Manfred T. Reetz and
• Hongchao Guo

Beilstein J. Org. Chem. 2005, 1, No. 3, doi:10.1186/1860-5397-1-3

• even two stereogenic centers. Ligands P18, P20 and P21[32] were used in the (S)-form. In the case of the menthyl-derivative P15, a single stereoisomer was employed, although the configuration at phosphorus is unknown.[33] The menthol-derived ligand P23 having the (S)-configuration at phosphorus was