Design and synthesis of quasi-diastereomeric molecules with unchanging central, regenerating axial and switchable helical chirality via cleavage and formation of Ni(II)–O and Ni(II)–N coordination bonds

• Vadim A. Soloshonok,
• José Luis Aceña,
• Hisanori Ueki and
• Jianlin Han

Beilstein J. Org. Chem. 2012, 8, 1920–1928, doi:10.3762/bjoc.8.223

• environment upon its configurational stabilization in complexes 5 and 6. Results and Discussion To build the real molecules to this design, we explored the preparation of imino–carbonyl ligands 13 (Scheme 3) by desymmetrization of achiral carbonyl–carbonyl ligands 12. Compounds 12 were prepared in the

• central, axial and helical chirality. Preparation of imino–carbonyl ligands 13 by desymmetrization of achiral carbonyl–carbonyl ligands 12. Preparation of complexes 14a,b and 15 by reactions of ligands 12 with glycine. Oxidation of enolates 16 and formation of complexes 19 and 20. Supporting Information

Asymmetric desymmetrization of meso-diols by C₂-symmetric chiral 4-pyrrolidinopyridines

• Hartmut Schedel,
• Keizo Kan,
• Yoshihiro Ueda,
• Kenji Mishiro,
• Keisuke Yoshida,
• Takumi Furuta and
• Takeo Kawabata

Beilstein J. Org. Chem. 2012, 8, 1778–1787, doi:10.3762/bjoc.8.203

• pyrrolidinopyridine framework as a catalytic site. Some of these organocatalysts effectively promoted asymmetric desymmetrization of meso-diols via enantioselective acylation. Keywords: acylation; desymmetrization; hydrogen bond; meso-diol; nucleophilic catalyst; organocatalysis; Introduction Since the pioneering

• pyrrolidine ring such as 3 were prepared from trans-4-hydroxy-L-proline. These catalysts were found to be moderately effective for the asymmetric desymmetrization of meso-diols [11]. C2-Symmetric PPY-catalyst 4 was found to be effective for the chemo- and regioselective acylation of carbohydrates [12][14][16

• ] and the chemoselective monoacylation of linear diols [17]. Here, we report the asymmetric desymmtrization of meso-diols by C2-symmetric PPY catalysts [20]. The effects of the functional side chains at C(2) and C(5) on the efficiency of the asymmetric desymmetrization are discussed. Some of the results

The crystal structure of the Dess–Martin periodinane

• Albert Schröckeneder,
• Desiree Stichnoth,
• Peter Mayer and
• Dirk Trauner

Beilstein J. Org. Chem. 2012, 8, 1523–1527, doi:10.3762/bjoc.8.172

• significantly different bond lengths (I1–O5 = 2.0670(13) Å, I1–O7 = 2.1141(13) Å), which desymmetrizes the molecule overall. This desymmetrization cannot be attributed to crystal-packing effects since it is also apparent in a structural model of 1 calculated by using DFT theory at the PBE0/LANL2DZdp level [10

Organocatalytic asymmetric addition of malonates to unsaturated 1,4-diketones

• Sergei Žari,
• Tiiu Kailas,
• Marina Kudrjashova,
• Mario Öeren,
• Ivar Järving,
• Toomas Tamm,
• Margus Lopp and
• Tõnis Kanger

Beilstein J. Org. Chem. 2012, 8, 1452–1457, doi:10.3762/bjoc.8.165

• ]. Therefore, new asymmetric additions of C-nucleophiles to unsaturated 1,4-diketones are highly in demand. The asymmetric desymmetrization of symmetric unsaturated 1,4-diketones is a very challenging target. si-Attack on one carbon atom of the double bond and re-attack on the other leads to the same

• investigated the organocatalytic approach to the asymmetric desymmetrization of the title compounds with malonates. Three types of organocatalysts providing noncovalent interactions were used for this purpose: Cinchona alkaloids (I–V), thiourea derivatives (VI, VII) and squaramide derivatives (VIII, IX

• -enantiomer. Conclusion We have developed a highly enantioselective method for the desymmetrization of aromatic unsaturated 1,4-diketones through organocatalytic reactions with malonates. The reaction is catalyzed by thiourea and squaramide derivatives with Cinchona alkaloids and affords products in very high

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

• backbone the sulfonimidoyl moiety leads to organocatalysts showing good reactivity in the catalytic desymmetrization of a cyclic meso-anhydride and moderate enantioselectivity in the catalytic asymmetric Biginelli reaction. Straightforward synthetic routes provide the newly designed thiourea-sulfoximine

• representative of each class was briefly tested in the desymmetrization of anhydride 4. Under the conditions described above for organocatalyst (S)-3 two catalyses were performed with (S)-12 (10 mol %) and (RS,SC)-19 (5 mol %). Whereas benzene-bridged sulfonimidoyl-containing thiourea (S)-12 provided the product

• hemiesters (5/ent-5). Apparently, both thioureas proved inappropriate for this reaction, and no further efforts were made to improve the anhydride desymmetrization with these types of organocatalysts. Next, the catalysis screening was focused on Biginelli reactions, which provide access to dihydropyrimidines

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

Brønsted acid-promoted azide–olefin [3 + 2] cycloadditions for the preparation of contiguous aminopolyols: The importance of disiloxane ring size to a diastereoselective, bidirectional approach to zwittermicin A

• Hubert Muchalski,
• Ki Bum Hong and
• Jeffrey N. Johnston

Beilstein J. Org. Chem. 2010, 6, 1206–1210, doi:10.3762/bjoc.6.138

• pure (−)-zwittermicin A (1) is based on a short synthesis of the C9–C15 aminopolyol core that takes advantage of its underlying C2 symmetry, as outlined in Scheme 1. Desymmetrization and functionalization of the bis(oxazolidine dione) 2 provides us with a foundation for the synthesis of 1 and would

Enantioselective synthesis of tricyclic amino acid derivatives based on a rigid 4-azatricyclo[5.2.1.0^2,6]decane skeleton

• Matthias Breuning,
• Tobias Häuser,
• Christian Mehler,
• Christian Däschlein,
• Carsten Strohmann,
• Andreas Oechsner and
• Holger Braunschweig

Beilstein J. Org. Chem. 2009, 5, No. 81, doi:10.3762/bjoc.5.81

• and 8 were successfully accomplished in 9–10 steps starting with inexpensive endo-carbic anhydride (10). The key stereochemical step was the desymmetrization of the meso-alkene 11 using Hayashi’s hydrosilylation/oxidation procedure, which provided the endo-alcohol 12 in 85% ee. The target molecules

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

• conditions resulted in a smooth conversion of the starting material into THF 89. Triol (+)-90 was obtained with lipase Amano AK desymmetrization. For the appropriate side chain attachment, the termini were differentiated to give lactone (−)-91. Reduction of (−)-91 followed by a Wittig reaction yielded fully

• controlled double cyclization of 230 allowed the selective formation of a single diastereomer 231 in one step, thus providing general access to annonaceous acetogenins containing trans/threo/trans or cis/threo/cis bis-THF core structures. Desymmetrization of diene 231 with AD-mix-β provided the known triol

Desymmetrization of 7-azabicycloalkenes by tandem olefin metathesis for the preparation of natural product scaffolds

• Wolfgang Maison,
• Marina Büchert and
• Nina Deppermann

Beilstein J. Org. Chem. 2007, 3, No. 48, doi:10.1186/1860-5397-3-48

• product scaffolds and have also been used for ring opening of strained carbo- and heterocycles. In this paper we demonstrate the potential of these reactions for the desymmetrization of 7-azabicycloalkenes. Results We have established efficient protocols for the desymmetrization of different 7

• -azabicycloalkenes by intra- and intermolecular tandem metathesis sequences with ruthenium based catalysts. Conclusion Desymmetrization of 7-azabicycloalkenes by olefin metathesis is an efficient process for the preparation of common natural product scaffolds such as pyrrolidines, indolizidines and isoindoles

• ][57][58][59][60][61] In this paper, we describe the extension of this work and show that desymmetrization of 7-azabicycloalkenes via RORCM leads to valuable natural product scaffolds. In this context, symmetrical derivatives of 7-azabicycloalkenes like 7 and 12 are extremely interesting substrates for