Organocatalyzed enantioselective desymmetrization of aziridines and epoxides

• Ping-An Wang

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

• (Figure 15). These novel chiral mono- and bisphosphine oxides were investigated as organocatalysts for the efficient enantioselective desymmetrization of meso-epoxides. Due to the lack of C2 symmetry of mono-phosphine oxides, they displayed lower reactivities and enantioselectivities than the bisphosphine

Host–guest complexes of mixed glycol-bipyridine cryptands: prediction of ion selectivity by quantum chemical calculations, part V

• Svetlana Begel,
• Ralph Puchta and
• Rudi van Eldik

Beilstein J. Org. Chem. 2013, 9, 1252–1268, doi:10.3762/bjoc.9.142

• mentioned, the beryllium dications are fourfold coordinated. In the case of [Be 2.2.bpy]2+, the structure with C1 symmetry is energetically more stable (−22.0 kcal/mol) than the one with C2 symmetry (−3.1 kcal/mol). The beryllium ion is here coordinated by two Nsp2, one Nsp3 bridgehead and one O donor atom

• . In [Be 2.bpy.bpy]2+, the coordination sphere of the cation consists of four nitrogen atoms, viz., three coming from bpy-groups and the fourth being a bridgehead nitrogen. According to this, the cryptate in the C1 symmetry, which is more stable than the C2 symmetry, shows two Nsp2–C–C–Nsp2 twist

• . Because of its small radius, it apparently does not need to twist the chelating group as much as one would expect from the extrapolation of the other values. Similar behavior can be ascribed to other small cations: Al3+, Li+ and Ga3+, while [Ga 2.2.bpy]3+ in C2 symmetry is present as a transition state

Asymmetric synthesis of a highly functionalized bicyclo[3.2.2]nonene derivative

• Toshiki Tabuchi,
• Daisuke Urabe and
• Masayuki Inoue

Beilstein J. Org. Chem. 2013, 9, 655–663, doi:10.3762/bjoc.9.74

• synthesis; C2-symmetry; catalysis; Diels–Alder reaction; Lewis acid; natural product; quaternary carbon; Introduction Ryanodine (Scheme 1) [1][2][3] is a potent modulator of the intracellular calcium release channels, known as ryanodine receptors [4][5]. Its complex architecture, including eight contiguous

• -demethyl-10,15-dideoxyryanodol [10] by taking advantage of the intrinsic C2-symmetry of the target molecule. In this synthesis, C2-symmetric compounds such as bicyclo[3.3.2]decene 1 were strategically designed, and application of pairwise functionalizations of these molecules minimized the total number of

Low-generation dendrimers with a calixarene core and based on a chiral C₂-symmetric pyrrolidine as iminosugar mimics

• Marco Marradi,
• Stefano Cicchi,
• Francesco Sansone,
• Alessandro Casnati and
• Andrea Goti

Beilstein J. Org. Chem. 2012, 8, 951–957, doi:10.3762/bjoc.8.107

• dendrimers, based on the C2-symmetric (3S,4S)-3,4-dihydoxypyrrolidine (1) unit, to a simple calix[4]arene scaffold (Figure 1). This allows a rapid increase of the valency of the iminosugar dendrimer in a reduced volume. The C2 symmetry of pyrrolidine 1, its ready accessibility from the “chiral pool” (L

Laterally substituted symmetric and nonsymmetric salicylideneimine-based bent-core mesogens

• Sonja Findeisen-Tandel,
• Wolfgang Weissflog,
• Ute Baumeister,
• Gerhard Pelzl,
• H. N. Shreenivasa Murthy and
• Channabasaveshwar V. Yelamaggad

Beilstein J. Org. Chem. 2012, 8, 129–154, doi:10.3762/bjoc.8.15

• of the suffixes P, A, F, s, and a, used for the characterization of banana phases, is also given there. In the SmCP phase the molecular long axis is tilted with respect to the layer normal, which corresponds to a C2 symmetry of the smectic layers. The combination of director tilt and polar order

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

• rapid access to pyridine derivatives such as 32 which almost has C2-symmetry. Compound 32 is derived from nitrile 31 and carboxylic acid 17 and was obtained in high yield after two steps. Products 34 and 35 were prepared from enantiopure acid 29 and racemic O-TBS-mandelonitrile 33. The diastereomeric

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

Synthesis and Diels–Alder cycloaddition reaction of norbornadiene and benzonorbornadiene dimers

• Bilal Nişancı,
• Erdin Dalkılıç,
• Murat Güney and
• Arif Daştan

Beilstein J. Org. Chem. 2009, 5, No. 39, doi:10.3762/bjoc.5.39

• chromatographic methods (Scheme 3). Structural Analyses The determination of the structures of dimers 7, 8 and dimers 16, 17 by spectroscopic methods was not simple because the Cs symmetry of the syn dimers and the C2 symmetry of the anti dimers and the free rotation around the central σ bond make them

An exceptional P-H phosphonite: Biphenyl- 2,2'-bisfenchylchlorophosphite and derived ligands (BIFOPs) in enantioselective copper- catalyzed 1,4-additions

• T. Kop-Weiershausen,
• J. Lex,
• J.-M. Neudörfl and
• B. Goldfuss

Beilstein J. Org. Chem. 2005, 1, No. 6, doi:10.1186/1860-5397-1-6

• °, Table 2). [68][69][70][71][72] Likewise, the pyramidality at the phosphorus atoms in BIFOPs distorts the inherent C2-symmetry of the biphenylbisfenchol units to asymmetry (C1). Fenchanes close to the phosphorus lone pairs (with FAA-lp) can be differentiated from fenchanes close to substituents at