Metal-mediated aminocatalysis provides mild conditions: Enantioselective Michael addition mediated by primary amino catalysts and alkali-metal ions

• Matthias Leven,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2013, 9, 155–165, doi:10.3762/bjoc.9.18

• -hydroxycoumarin (1) to prochiral α,β-unsaturated ketones. Instead of acid additives, which sometimes lead to decomposition of sensitive components [18], alkali-metal ions are employed as very mild Lewis acids (Scheme 1). The activation of Michael acceptors by iminium ions enables asymmetric additions of 4

• , which are able to form imine complexes with prochiral α,β-unsaturated ketones, which could be detected by ESIMS spectrometry in an exemplary case. It was found that the Lewis acidities of the alkali metal ions are strong enough to activate the imine homologous Michael systems for nucleophilic addition

Cation affinity numbers of Lewis bases

• Christoph Lindner,
• Raman Tandon,
• Boris Maryasin,
• Evgeny Larionov and
• Hendrik Zipse

Beilstein J. Org. Chem. 2012, 8, 1406–1442, doi:10.3762/bjoc.8.163

• chiral or prochiral carbon electrophiles may constitute part of the overall stereodifferentiating process. The potential of differentiating the faces of a prochiral electrophile can be quantified for Lewis bases through affinity numbers to a prochiral reference cation. The potential of this approach has

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

• Michael addition of unprotected 3-prochiral oxindoles 1 to 1,4-naphthoquinone. Quinidine derivative (DHQD)2PYR was found to be able to catalyze this reaction in up to 83% ee, with moderate to excellent yields. This method could be used for the synthesis of enantioenriched 3,3-diaryloxindoles, and the

• enantioenriched 3-hydroxyoxindoles [22][23][24]. For the synthesis of chiral 3-aminooxindoles, we developed the first example of catalytic asymmetric addition of nucleophiles to isatin-derived ketoimines using TMSCN [25] and the amination of unprotected 3-prochiral oxindoles using di-tert-butyl azodicarboxylate

• -diaryloxindoles. It also came to our attention that, while the addition of 3-prochiral oxindole to a variety of Michael acceptors had been studied [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46], the use of quinones as the Michael acceptor had not been realized. Therefore, in this letter we are going

Cyclodextrin nanosponge-sensitized enantiodifferentiating photoisomerization of cyclooctene and 1,3-cyclooctadiene

• Wenting Liang,
• Cheng Yang,
• Masaki Nishijima,
• Gaku Fukuhara,
• Tadashi Mori,
• Andrea Mele,
• Franca Castiglione,
• Fabrizio Caldera,
• Francesco Trotta and
• Yoshihisa Inoue

Beilstein J. Org. Chem. 2012, 8, 1305–1311, doi:10.3762/bjoc.8.149

• chirality transfer from chiral host to prochiral substrate through the long-lasting intimate supramolecular contacts of guest substrate(s) with the chiral host in both the ground and excited states [4][5][6][7][8][9][10]. Various types of chiral supramolecular hosts, including modified zeolites [11

Synthesis and structure of tricarbonyl(η⁶-arene)chromium complexes of phenyl and benzyl D-glycopyranosides

• Thomas Ziegler and
• Ulrich Heber

Beilstein J. Org. Chem. 2012, 8, 1059–1070, doi:10.3762/bjoc.8.118

• (MeCN)3Cr(CO)3 were also unsuccessful (no further experimental details shown). Next, we also prepared some sugar-derived tricarbonylchromium complexes of glycosides having a prochiral aglycon, i.e., an ortho-substituted phenyl or benzyl aglycon. Glycosides 1m [21] and 1q [22] were prepared according to

• Ar and exclusion of light. Synthesis of tricarbonylchromium complexes 2m–q from glycosides 1m–q containing a prochiral aglycon and Cr(CO)6 in di-n-butylether/THF 9:1 at 140 °C under Ar in the dark. Chemical shifts (δ in ppm) of the protons of compounds 1a and 2a derived from the 1H NMR spectra of the

Synthesis of axially chiral oxazoline–carbene ligands with an N-naphthyl framework and a study of their coordination with AuCl·SMe₂

• Feijun Wang,
• Shengke Li,
• Mingliang Qu,
• Mei-Xin Zhao,
• Lian-Jun Liu and
• Min Shi

Beilstein J. Org. Chem. 2012, 8, 726–731, doi:10.3762/bjoc.8.81

• reported a type of NHC–Au(I) complexes 2 containing C2-symmetric bis(NHC)-ligands with two imidazolin-2-ylidene moieties on a chiral dioxolane backbone, produced in up to 95% ee by hydrogenation of a prochiral alkene [11]. Recently, Toste and co-workers reported a novel family of axially chiral (acyclic

Bromine–lithium exchange: An efficient tool in the modular construction of biaryl ligands

• Laurence Bonnafoux,
• Frédéric R. Leroux and
• Françoise Colobert

Beilstein J. Org. Chem. 2011, 7, 1278–1287, doi:10.3762/bjoc.7.148

• routes to synthetically challenging aryl halide precursors have been devised. A. Alexakis et al. recently achieved a significant breakthrough. They succeeded in the desymmetrization of prochiral polybrominated [32][51] compounds by an asymmetric bromine–lithium exchange in the presence of a

• stoichiometric amount of chiral diamines. An enantiomeric excess of up to 63% was obtained [67]. H. Kagan et al. reported the desymmetrization of prochiral aromatic or vinylic dihalide substrates by halogen–metal exchange in the presence of a stoichiometric amount of diamines, with enantiomeric excess up to 26

A simple and convenient one-pot synthesis of substituted isoindolin-1-ones via lithiation, substitution and cyclization of N'-benzyl-N,N-dimethylureas

• Keith Smith,
• Gamal A. El-Hiti,
• Amany S. Hegazy and
• Benson Kariuki

Beilstein J. Org. Chem. 2011, 7, 1219–1227, doi:10.3762/bjoc.7.142

• report full details of that work, extend the scope of the reaction and examine the diastereoselectivity of the reaction with prochiral electrophiles. Results and Discussion As noted above, when lithiation of 1 was carried out at 0 °C rather than at −20 °C prior to reaction with an electrophile, lower

Chiral gold(I) vs chiral silver complexes as catalysts for the enantioselective synthesis of the second generation GSK-hepatitis C virus inhibitor

• María Martín-Rodríguez,
• Carmen Nájera,
• José M. Sansano,
• Abel de Cózar and
• Fernando P. Cossío

Beilstein J. Org. Chem. 2011, 7, 988–996, doi:10.3762/bjoc.7.111

• of the 1,3-DC employing chiral metallic Lewis bases arises from the blockage of one of the prochiral faces [40]. In this way, our results (in terms of DFT calculations) show that there is only one energetically accessible conformation due to the high substitution of the leucine-derived ylide (Figure

•  3). In this reactive complex there is an effective blockage of the (2re,5si) prochiral face of the ylide. Therefore, the predicted stereochemical outcome corresponds to the exclusive formation of the (2S,4S,5R)-5b cycloadduct, the same as that obtained experimentally. As shown in Figure 3, the

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

Asymmetric synthesis of tertiary thiols and thioethers

• Jonathan Clayden and
• Paul MacLellan

Beilstein J. Org. Chem. 2011, 7, 582–595, doi:10.3762/bjoc.7.68

• simple tertiary alcohols is generally achieved by controlling enantiofacial selectivity in nucleophilic attack on a prochiral ketone [10], comparable approaches to tertiary thiols 1 are not practical due to the instability of thioketones, their tendency to undergo nucleophilic attack at sulfur rather

Application of the diastereoselective photodeconjugation of α,β-unsaturated esters to the synthesis of gymnastatin H

• Ludovic Raffier and
• Olivier Piva

Beilstein J. Org. Chem. 2011, 7, 151–155, doi:10.3762/bjoc.7.21

• enantioselective versions. Starting from α-substituted esters 3 in the presence of a catalytic amount of an enantiomerically pure bicyclic amino alcohol 4 – derived from camphor –, the protonation of the prochiral photodienol can be achieved with an ee up to 91% [5]. This value is one of the highest values

Development of dynamic kinetic resolution on large scale for (±)-1-phenylethylamine

• Lisa K. Thalén and
• Jan-E. Bäckvall

Beilstein J. Org. Chem. 2010, 6, 823–829, doi:10.3762/bjoc.6.97

• for their preparation that are applicable on multigram scale. They can be prepared by resolution of amines, hydrogenation of prochiral imines and enamines [1][2], alkylation of prochiral imines [3], aminohydroxylation of alkenes [4], transamination of prochiral ketones [5][6][7], and reductive

• amination of prochiral ketones [8]. Of these methods kinetic resolution using enzymes is often favored due to its simplicity [9][10]. The main disadvantages of kinetic resolution are that only a maximum yield of 50% can be achieved and that the remaining unreacted starting material must be removed from the

Shelf-stable electrophilic trifluoromethylating reagents: A brief historical perspective

• Norio Shibata,
• Andrej Matsnev and
• Dominique Cahard

Beilstein J. Org. Chem. 2010, 6, No. 65, doi:10.3762/bjoc.6.65

• chiral groups thus giving the possibility to achieve enantioselective trifluoromethylation of prochiral substrates. This is one of the important issues that is only partially solved in fluoro-organic chemistry. Therefore, chiral reagent 18 was designed and synthesized from (1R)-(+)-camphor as shown in

A novel and efficient method to prepare 2-aryltetrahydrofuran-2-ylphosphonic acids

• Vsevolod V. Komissarov,
• Anatoly M. Kritzyn and
• Jouko J. Vepsäläinen

Beilstein J. Org. Chem. 2010, 6, No. 63, doi:10.3762/bjoc.6.63

• from MS and NMR spectral data. The cyclic structures of the end products were verified not only from molecular ion peaks in the mass spectra but also from 1H NMR data, in which three CH2-groups give rise to six chemical shifts. This phenomenon exists if a chiral center (sometimes a prochiral center) is

Concise methods for the synthesis of chiral polyoxazolines and their application in asymmetric hydrosilylation

• Wei Jie Li,
• Zun Le Xu and
• Sheng Xiang Qiu

Beilstein J. Org. Chem. 2010, 6, No. 29, doi:10.3762/bjoc.6.29

• prochiral ketones. In particular, asymmetric catalysis provides organic chemists with a unique tool for their efficient synthesis [23], although none of these are, as yet, optimal [24][25][26]. In recent years, metal-catalyzed hydrosilylation of ketones has been investigated using chiral ligands [27][28][29

• ][30][31][32][33], while enantioselective hydrogenation of prochiral ketones to optically active secondary alcohols is among the most fundamental subjects in modern synthetic chemistry. In this article, with the new polyoxazoline ligands in hand, the Rh-catalyzed hydrosilylation of aromatic ketones was

• alcohols, because the enantioselectivities were determined solely by the chirality of oxazoline rings derived from the chiral amino alcohols. The reduction of various prochiral aryl-substituted ketones was examined in order to evaluate the influence of ligand 2 on Rh(I)-catalyzed asymmetric hydrosilylation

Large- scale ruthenium- and enzyme- catalyzed dynamic kinetic resolution of (rac)-1-phenylethanol

• Krisztián Bogár,
• Belén Martín-Matute and
• Jan-E. Bäckvall

Beilstein J. Org. Chem. 2007, 3, No. 50, doi:10.1186/1860-5397-3-50

• natural products. [1][2][3][4] A few methods have been developed for the enantioselective synthesis of chiral alcohols including catalytic asymmetric hydrogenation [5][6][7][8][9][10][11][12][13][14] and enantioselective hydride addition [15][16] of prochiral ketones, asymmetric dialkylzinc addition to

Conformational rigidity of silicon- stereogenic silanes in asymmetric catalysis: A comparative study

• Sebastian Rendler and
• Martin Oestreich

Beilstein J. Org. Chem. 2007, 3, No. 9, doi:10.1186/1860-5397-3-9

• formation occurs between the stereogenic silicon and the prochiral carbon therefore entailing their close proximity. The newly formed stereogenic carbon is directly connected to the former source of chiral information. In contrast, the decisive asymmetrically substituted carbon atom in the alcohol substrate

Synthesis and glycosidase inhibitory activity of new hexa- substituted C8-glycomimetics

• Olivia Andriuzzi,
• Christine Gravier-Pelletier,
• Gildas Bertho,
• Thierry Prangé and
• Yves Le Merrer

Beilstein J. Org. Chem. 2005, 1, No. 12, doi:10.1186/1860-5397-1-12

• H2 (proS), H8 and H7 (proS) indicate a pseudo-equatorial position of protons H2 (proS) and H7 (proS). NOE measurements and finally Molecular Dynamic calculations using Insight II software (Biosym Technologies, San Diego, CA) allowed to deduce the structure of 11 (Figure 4). Prochiral H2 (proS) and H7

• protons (in bold) of the upper face of the C8 ring. Prochiral 1H are labelled pR or pS. X-ray structure of epoxide 7 (upper) and sulfate 9 (down) solved using SHELXS and anisotropically refined using SHELXL programs [38]. Reagents and conditions: (a) OsO4, NMO, tBuOH, rt; (b) TFA, H2O, rt. Reagents and