Chiral amplification in a cyanobiphenyl nematic liquid crystal doped with helicene-like derivatives

• Alberta Ferrarini,
• Silvia Pieraccini,
• Stefano Masiero and
• Gian Piero Spada

Beilstein J. Org. Chem. 2009, 5, No. 50, doi:10.3762/bjoc.5.50

• conformer of 5, the molecular surface has negative helicity along the x axis, whereas the helicity is positive along the y and z axes. This is in agreement with the P helical stereochemical descriptor of the chiral dopants under investigation, which is defined with respect to the helix axis (y). In the case

• under investigation. We can see even more substantial differences between Qii components, with particularly low values predicted for the 5-I conformer. As a result of the surface chirality and the orientational behavior, induction of right-handed cholesterics is predicted for our dopants. The trend of

Preparation and Diels–Alder/cross coupling reactions of a 2-diethanolaminoboron- substituted 1,3-diene

• Liqiong Wang,
• Cynthia S. Day,
• Marcus W. Wright and
• Mark E. Welker

Beilstein J. Org. Chem. 2009, 5, No. 45, doi:10.3762/bjoc.5.45

• earlier work [10] and those cobaloxime dienes consistently favored the s-cis conformation in the solid state. Diene 2 is in the s-trans conformation in the solid state (Figure 1) but in this case we suspect that the preference for the s-trans conformer is due to intermolecular hydrogen bonding between the

• N–H and one of the adjacent molecule’s boronate oxygen atoms. This hydrogen bonding would make a C(2)–C(3) dihedral angle of 50–60° (on the order of those we observed in cobaloxime diene solid state structures) unfavorable. At 25 °C in CDCl3, we saw no evidence for the s-cis conformer by NOESY. In

Synthesis of rigidified flavin–guanidinium ion conjugates and investigation of their photocatalytic properties

• Harald Schmaderer,
• Mouchumi Bhuyan and
• Burkhard König

Beilstein J. Org. Chem. 2009, 5, No. 26, doi:10.3762/bjoc.5.26

• spectra of compounds 1 and 2 revealed several NOE contacts, but the flexibility of the molecule did not allow the determination of preferred conformations. The most stable conformer of compound 1 in the gas phase was determined by computational methods (semi-empirical AM1, Spartan program package, Figure

Synthesis of deep- cavity fluorous calix[4]arenes as molecular recognition scaffolds

• Maksim Osipov,
• Qianli Chu,
• Steven J. Geib,
• Dennis P. Curran and
• Stephen G. Weber

Beilstein J. Org. Chem. 2008, 4, No. 36, doi:10.3762/bjoc.4.36

• enhance the formation of a single conformer [12]. Of the four possible conformations, the cone is the most desirable for molecular recognition and sensing applications because it has the largest available surface area for host-guest interactions [10]. With appropriate functionality and conformation, the

• ]arene [27] 2. Using NaH/DMF, conditions known to favor reaction in the cone conformation [12], 2 was alkylated with 3-(perfluorohexyl)propyl iodide to give cone conformer 3a as the dominant tetraalkylated product in 61% yield after recrystallization (Scheme 1). However, 3a did not exhibit the desired

Single and double stereoselective fluorination of (E)-allylsilanes

• Marcin Sawicki,
• Angela Kwok,
• Matthew Tredwell and
• Véronique Gouverneur

Beilstein J. Org. Chem. 2007, 3, No. 34, doi:10.1186/1860-5397-3-34

• other than "F+", an anti approach with respect to the silyl group prevails with preferential formation of the syn (E) isomer. [18][19][20][21] This stereochemical outcome suggests that the major reaction pathway involves the reactive conformer I leading, after addition of the electrophile, to a

Reactions of glycidyl derivatives with ambident nucleophiles; part 2: amino acid derivatives

• Gerald Dyker,
• Andreas Thöne and
• Gerald Henkel

Beilstein J. Org. Chem. 2007, 3, No. 28, doi:10.1186/1860-5397-3-28

• from a weak intramolecular hydrogen bond. According to ab initio calculations for cis-9a, (B3LYP, 6-31G*, zero point energy included) this structure is indeed 1.9 kcal/mol more stable than its exo-oriented conformer and 2.2 kcal/mol more stable than its trans-stereoisomer. Conclusion In summary, we

Photosonochemical catalytic ring opening of α-epoxyketones

• Hamid R. Memarian and
• Ali Saffar-Teluri

Beilstein J. Org. Chem. 2007, 3, No. 2, doi:10.1186/1860-5397-3-2

• more stable conformer of the intermediate 7 can be formed through interaction of oxygen lone pair of carbonyl group with carbocation center (Scheme 4, intermediate 8). This leads to the preferred nucleophilic attack of methanol to the carbon atom at the less hindered site (VII) to form the cis-isomers

The vicinal difluoro motif: The synthesis and conformation of erythro- and threo- diastereoisomers of 1,2-difluorodiphenylethanes, 2,3-difluorosuccinic acids and their derivatives

• David O'Hagan,
• Henry S. Rzepa,
• Martin Schüler and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2006, 2, No. 19, doi:10.1186/1860-5397-2-19

• Information File 2). Of the three staggered conformers of the erythro-13 isomer two are enantiomeric and have identical energies thus analysis of erythro-13 is reduced to a comparison of the energies of conformers a and b. Conformer a emerges as the more stable in the gas phase, with this stability

• originating predominantly from entropy and zero-point energy corrections (1.06 kcal/mol). This is also the conformer that most closely represents the X-ray structure (Figure 1). The solvent correction (which takes into account free energy differences associated with the solvent cavity, but does not allow for

• and appears to be dominated by solvation of the trans relationship of the aryl rings and the zero dipole moment, although the smaller 3JHH coupling of 2.6 Hz and the slightly larger 3JHF coupling of 15 Hz in the NMR, measurement does suggest some contribution of conformer b in solution. The threo-13

Methods for the synthesis of polyhydroxylated piperidines by diastereoselective dihydroxylation: Exploitation in the two-directional synthesis of aza-C-linked disaccharide derivatives

• Andrew Kennedy,
• Adam Nelson and
• Alexis Perry

Beilstein J. Org. Chem. 2005, 1, No. 2, doi:10.1186/1860-5397-1-2

• interactions that are necessarily incurred.[48][49] In contrast, 22D populates a distorted boat conformation, presumably in order to avoid unfavourable 1,3-diaxial interactions between the C-4 acetoxy group and C-2 and C-6 methylene groups of the alternative chair conformer. Diagnostic nOe connections for the